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Jackson-Bell 96
1/4/2013 9:06:53 AMJohn
I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
1/4/2013 11:49:41 AMWALTER FROEHLICH
HI JOHN:

SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.

WALTER-W2WIQ


:I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:

1/4/2013 10:40:24 PMEdd
:HI JOHN:
:
:SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:
:WALTER-W2WIQ
:
:









Sir John . . . .


Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.


(And that you have a moderately healthy length of aerial wire being connected to the set.)


You say:



It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.



In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..


That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
up the overall RF gain to get the set working.


Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.


OR


Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?


You say:



Also, from the screen of the 1st 24 to ground is a .5 capacitor.



That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.


As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.

Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.


Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?

Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.


Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.


On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.


Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.


Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.


But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.


So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).


The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.


You ask . . .What is dat dere 300 ohm resistor in dere for ?


Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .


Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.


That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .


On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.


That will then be squelching the gain capabilities of those frontal RF tubes severely.


Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )


But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".


As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.


So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.


Re Review:


(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)




A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.


Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.


With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.


That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.


Thassittt . . .




Finally you say:



Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia



No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.


If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.


Then fire up the set and evaluate your audio.


With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.


That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !


The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.

And that's the rest of the story . . . . .




73's de Edd




Don't force it ! ! ! . . . . get a bigger hammer.







:
:
:
:
:
:
::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::
:
:

1/5/2013 8:31:06 AMJohn
Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?

::HI JOHN:
::
::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
::
::WALTER-W2WIQ
::
::
:
:

:
:
:
:
:
:
:
:
:
:
:
:Sir John . . . .
:
:
:Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
:
:
:
:(And that you have a moderately healthy length of aerial wire being connected to the set.)
:
:
:
:
:You say:
:
:
:
:It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
:
:
:
:In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
:
:
:That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:up the overall RF gain to get the set working.
:
:
:Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
:
:
:OR
:
:
:Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
:
:
:You say:
:
:
:
:Also, from the screen of the 1st 24 to ground is a .5 capacitor.
:
:
:
:That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
:
:
:As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
:
:
:
:Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
:
:
:Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
:
:
:
:Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
:
:
:Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
:
:
:On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
:
:
:Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
:
:
:Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
:
:
:But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
:
:
:So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
:
:
:The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
:
:
:You ask . . .What is dat dere 300 ohm resistor in dere for ?
:
:
:Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
:
:
:Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
:
:
:That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
:
:
:On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
:
:
:That will then be squelching the gain capabilities of those frontal RF tubes severely.
:
:
:Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
:
:
:But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
:
:
:As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
:
:
:So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
:
:
:Re Review:
:
:
:(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
:
:
:
:
:
:
:A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
:
:
:Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
:
:
:With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
:
:
:That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
:
:
:Thassittt . . .
:
:
:
:
:Finally you say:
:
:
:
:Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
:
:
:
:No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
:
:
:If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
:
:
:Then fire up the set and evaluate your audio.
:
:
:With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
:
:
:That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
:
:
:The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
:
:
:
:And that's the rest of the story . . . . .
:
:
:
:
:
:
:
:
:73's de Edd
:
:
:
:
:
:Don't force it ! ! ! . . . . get a bigger hammer.
:
:
:
:
:
:
:
:
:

:
:
:
::
::
::
::
::
::
:::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:::
::
::
:
:

1/5/2013 10:20:12 AMNorm Leal
John

Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.

With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.

With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.

http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf

Norm

:Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:
:
:
:
:
:::HI JOHN:
:::
:::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::
:::WALTER-W2WIQ
:::
:::
::
::

::
::
::
::
::
::
::
::
::
::
::
::Sir John . . . .
::
::
::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::
::
::
::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::
::
::
::
::You say:
::
::
::
::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::
::
::
::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::
::
::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::up the overall RF gain to get the set working.
::
::
::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::
::
::OR
::
::
::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::
::
::You say:
::
::
::
::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::
::
::
::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::
::
::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::
::
::
::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::
::
::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::
::
::
::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::
::
::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::
::
::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::
::
::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::
::
::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::
::
::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::
::
::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::
::
::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::
::
::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::
::
::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::
::
::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::
::
::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::
::
::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::
::
::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::
::
::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::
::
::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::
::
::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::
::
::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::
::
::Re Review:
::
::
::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::
::
::
::
::
::
::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::
::
::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::
::
::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::
::
::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::
::
::Thassittt . . .
::
::
::
::
::Finally you say:
::
::
::
::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::
::
::
::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::
::
::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::
::
::Then fire up the set and evaluate your audio.
::
::
::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::
::
::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::
::
::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::
::
::
::And that's the rest of the story . . . . .
::
::
::
::
::
::
::
::
::73's de Edd
::
::
::
::
::
::Don't force it ! ! ! . . . . get a bigger hammer.
::
::
::
::
::
::
::
::
::

::
::
::
:::
:::
:::
:::
:::
:::
::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::
:::
:::
::
::
:
:

1/8/2013 9:43:00 AMJohn
I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John


:John
:
: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
:
:With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
:
:With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
:
:http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
:
:Norm
:
:
:
::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
::
::
::
::
::
::::HI JOHN:
::::
::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
::::
::::WALTER-W2WIQ
::::
::::
:::
:::

:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::
:::Sir John . . . .
:::
:::
:::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
:::
:::
:::
:::(And that you have a moderately healthy length of aerial wire being connected to the set.)
:::
:::
:::
:::
:::You say:
:::
:::
:::
:::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
:::
:::
:::
:::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
:::
:::
:::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:::up the overall RF gain to get the set working.
:::
:::
:::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
:::
:::
:::OR
:::
:::
:::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
:::
:::
:::You say:
:::
:::
:::
:::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
:::
:::
:::
:::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
:::
:::
:::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
:::
:::
:::
:::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
:::
:::
:::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
:::
:::
:::
:::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
:::
:::
:::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
:::
:::
:::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
:::
:::
:::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
:::
:::
:::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
:::
:::
:::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
:::
:::
:::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
:::
:::
:::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
:::
:::
:::You ask . . .What is dat dere 300 ohm resistor in dere for ?
:::
:::
:::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
:::
:::
:::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
:::
:::
:::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
:::
:::
:::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
:::
:::
:::That will then be squelching the gain capabilities of those frontal RF tubes severely.
:::
:::
:::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
:::
:::
:::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
:::
:::
:::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
:::
:::
:::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
:::
:::
:::Re Review:
:::
:::
:::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
:::
:::
:::
:::
:::
:::
:::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
:::
:::
:::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
:::
:::
:::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
:::
:::
:::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
:::
:::
:::Thassittt . . .
:::
:::
:::
:::
:::Finally you say:
:::
:::
:::
:::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
:::
:::
:::
:::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
:::
:::
:::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
:::
:::
:::Then fire up the set and evaluate your audio.
:::
:::
:::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
:::
:::
:::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
:::
:::
:::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
:::
:::
:::
:::And that's the rest of the story . . . . .
:::
:::
:::
:::
:::
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::Don't force it ! ! ! . . . . get a bigger hammer.
:::
:::
:::
:::
:::
:::
:::
:::
:::

:::
:::
:::
::::
::::
::::
::::
::::
::::
:::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:::::
::::
::::
:::
:::
::
::
:
:

1/8/2013 9:53:05 PMNorm Leal
John

Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.

Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.

Norm

:I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
:
:
::John
::
:: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
::
::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
::
::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
::
::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
::
::Norm
::
::
::
:::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:::
:::
:::
:::
:::
:::::HI JOHN:
:::::
:::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::::
:::::WALTER-W2WIQ
:::::
:::::
::::
::::

::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::
::::Sir John . . . .
::::
::::
::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::::
::::
::::
::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::::
::::
::::
::::
::::You say:
::::
::::
::::
::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::::
::::
::::
::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::::
::::
::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::::up the overall RF gain to get the set working.
::::
::::
::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::::
::::
::::OR
::::
::::
::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::::
::::
::::You say:
::::
::::
::::
::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::::
::::
::::
::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::::
::::
::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::::
::::
::::
::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::::
::::
::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::::
::::
::::
::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::::
::::
::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::::
::::
::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::::
::::
::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::::
::::
::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::::
::::
::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::::
::::
::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::::
::::
::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::::
::::
::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::::
::::
::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::::
::::
::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::::
::::
::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::::
::::
::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::::
::::
::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::::
::::
::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::::
::::
::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::::
::::
::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::::
::::
::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::::
::::
::::Re Review:
::::
::::
::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::::
::::
::::
::::
::::
::::
::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::::
::::
::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::::
::::
::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::::
::::
::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::::
::::
::::Thassittt . . .
::::
::::
::::
::::
::::Finally you say:
::::
::::
::::
::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::::
::::
::::
::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::::
::::
::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::::
::::
::::Then fire up the set and evaluate your audio.
::::
::::
::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::::
::::
::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::::
::::
::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::::
::::
::::
::::And that's the rest of the story . . . . .
::::
::::
::::
::::
::::
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::Don't force it ! ! ! . . . . get a bigger hammer.
::::
::::
::::
::::
::::
::::
::::
::::
::::

::::
::::
::::
:::::
:::::
:::::
:::::
:::::
:::::
::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/9/2013 2:38:58 PMJohn
I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John


:John
:
: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
:
: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
:
:Norm
:
:
:
::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
::
::
:::John
:::
::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
:::
:::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
:::
:::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
:::
:::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
:::
:::Norm
:::
:::
:::
::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
::::
::::
::::
::::
::::
::::::HI JOHN:
::::::
::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
::::::
::::::WALTER-W2WIQ
::::::
::::::
:::::
:::::

:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::Sir John . . . .
:::::
:::::
:::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
:::::
:::::
:::::
:::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
:::::
:::::
:::::
:::::
:::::You say:
:::::
:::::
:::::
:::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
:::::
:::::
:::::
:::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
:::::
:::::
:::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:::::up the overall RF gain to get the set working.
:::::
:::::
:::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
:::::
:::::
:::::OR
:::::
:::::
:::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
:::::
:::::
:::::You say:
:::::
:::::
:::::
:::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
:::::
:::::
:::::
:::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
:::::
:::::
:::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
:::::
:::::
:::::
:::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
:::::
:::::
:::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
:::::
:::::
:::::
:::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
:::::
:::::
:::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
:::::
:::::
:::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
:::::
:::::
:::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
:::::
:::::
:::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
:::::
:::::
:::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
:::::
:::::
:::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
:::::
:::::
:::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
:::::
:::::
:::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
:::::
:::::
:::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
:::::
:::::
:::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
:::::
:::::
:::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
:::::
:::::
:::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
:::::
:::::
:::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
:::::
:::::
:::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
:::::
:::::
:::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
:::::
:::::
:::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
:::::
:::::
:::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
:::::
:::::
:::::Re Review:
:::::
:::::
:::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
:::::
:::::
:::::
:::::
:::::
:::::
:::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
:::::
:::::
:::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
:::::
:::::
:::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
:::::
:::::
:::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
:::::
:::::
:::::Thassittt . . .
:::::
:::::
:::::
:::::
:::::Finally you say:
:::::
:::::
:::::
:::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
:::::
:::::
:::::
:::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
:::::
:::::
:::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
:::::
:::::
:::::Then fire up the set and evaluate your audio.
:::::
:::::
:::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
:::::
:::::
:::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
:::::
:::::
:::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
:::::
:::::
:::::
:::::And that's the rest of the story . . . . .
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::73's de Edd
:::::
:::::
:::::
:::::
:::::
:::::Don't force it ! ! ! . . . . get a bigger hammer.
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::
:::::

:::::
:::::
:::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/9/2013 9:26:33 PMNorm Leal
John

Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.

Even if 1/2 was open you would still hear radio. The circuit is push-pull.

Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?

Norm
:I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
:
:
:
:
::John
::
:: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
::
:: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
::
::Norm
::
::
::
:::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
:::
:::
::::John
::::
:::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
::::
::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
::::
::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
::::
::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
::::
::::Norm
::::
::::
::::
:::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:::::
:::::
:::::
:::::
:::::
:::::::HI JOHN:
:::::::
:::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::::::
:::::::WALTER-W2WIQ
:::::::
:::::::
::::::
::::::

::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::Sir John . . . .
::::::
::::::
::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::::::
::::::
::::::
::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::::::
::::::
::::::
::::::
::::::You say:
::::::
::::::
::::::
::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::::::
::::::
::::::
::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::::::
::::::
::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::::::up the overall RF gain to get the set working.
::::::
::::::
::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::::::
::::::
::::::OR
::::::
::::::
::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::::::
::::::
::::::You say:
::::::
::::::
::::::
::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::::::
::::::
::::::
::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::::::
::::::
::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::::::
::::::
::::::
::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::::::
::::::
::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::::::
::::::
::::::
::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::::::
::::::
::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::::::
::::::
::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::::::
::::::
::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::::::
::::::
::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::::::
::::::
::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::::::
::::::
::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::::::
::::::
::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::::::
::::::
::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::::::
::::::
::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::::::
::::::
::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::::::
::::::
::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::::::
::::::
::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::::::
::::::
::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::::::
::::::
::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::::::
::::::
::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::::::
::::::
::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::::::
::::::
::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::::::
::::::
::::::Re Review:
::::::
::::::
::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::::::
::::::
::::::
::::::
::::::
::::::
::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::::::
::::::
::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::::::
::::::
::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::::::
::::::
::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::::::
::::::
::::::Thassittt . . .
::::::
::::::
::::::
::::::
::::::Finally you say:
::::::
::::::
::::::
::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::::::
::::::
::::::
::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::::::
::::::
::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::::::
::::::
::::::Then fire up the set and evaluate your audio.
::::::
::::::
::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::::::
::::::
::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::::::
::::::
::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::::::
::::::
::::::
::::::And that's the rest of the story . . . . .
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::Don't force it ! ! ! . . . . get a bigger hammer.
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::

::::::
::::::
::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/10/2013 2:41:06 PMJohn
With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John


:John
:
: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
:
: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
:
: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
:
:Norm
::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
::
::
::
::
:::John
:::
::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
:::
::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
:::
:::Norm
:::
:::
:::
::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
::::
::::
:::::John
:::::
::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
:::::
:::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
:::::
:::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
:::::
:::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
:::::
:::::Norm
:::::
:::::
:::::
::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
::::::
::::::
::::::
::::::
::::::
::::::::HI JOHN:
::::::::
::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
::::::::
::::::::WALTER-W2WIQ
::::::::
::::::::
:::::::
:::::::

:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::Sir John . . . .
:::::::
:::::::
:::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
:::::::
:::::::
:::::::
:::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
:::::::
:::::::
:::::::
:::::::
:::::::You say:
:::::::
:::::::
:::::::
:::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
:::::::
:::::::
:::::::
:::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
:::::::
:::::::
:::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:::::::up the overall RF gain to get the set working.
:::::::
:::::::
:::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
:::::::
:::::::
:::::::OR
:::::::
:::::::
:::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
:::::::
:::::::
:::::::You say:
:::::::
:::::::
:::::::
:::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
:::::::
:::::::
:::::::
:::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
:::::::
:::::::
:::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
:::::::
:::::::
:::::::
:::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
:::::::
:::::::
:::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
:::::::
:::::::
:::::::
:::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
:::::::
:::::::
:::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
:::::::
:::::::
:::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
:::::::
:::::::
:::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
:::::::
:::::::
:::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
:::::::
:::::::
:::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
:::::::
:::::::
:::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
:::::::
:::::::
:::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
:::::::
:::::::
:::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
:::::::
:::::::
:::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
:::::::
:::::::
:::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
:::::::
:::::::
:::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
:::::::
:::::::
:::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
:::::::
:::::::
:::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
:::::::
:::::::
:::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
:::::::
:::::::
:::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
:::::::
:::::::
:::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
:::::::
:::::::
:::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
:::::::
:::::::
:::::::Re Review:
:::::::
:::::::
:::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
:::::::
:::::::
:::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
:::::::
:::::::
:::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
:::::::
:::::::
:::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
:::::::
:::::::
:::::::Thassittt . . .
:::::::
:::::::
:::::::
:::::::
:::::::Finally you say:
:::::::
:::::::
:::::::
:::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
:::::::
:::::::
:::::::
:::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
:::::::
:::::::
:::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
:::::::
:::::::
:::::::Then fire up the set and evaluate your audio.
:::::::
:::::::
:::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
:::::::
:::::::
:::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
:::::::
:::::::
:::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
:::::::
:::::::
:::::::
:::::::And that's the rest of the story . . . . .
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::73's de Edd
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::Don't force it ! ! ! . . . . get a bigger hammer.
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::

:::::::
:::::::
:::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
:::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:::::::::
::::::::
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/10/2013 3:44:13 PMNorm Leal
John

Any chance the 250 ohm, near bottom of the schematic, is open? Measure DC voltage between filament, pin #12, of a 47 and chassis. Should be around 15 volts.

Norm

:With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John
:
:
::John
::
:: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
::
:: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
::
:: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
::
::Norm
:::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
:::
:::
:::
:::
::::John
::::
:::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
::::
:::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
::::
::::Norm
::::
::::
::::
:::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
:::::
:::::
::::::John
::::::
:::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
::::::
::::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
::::::
::::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
::::::
::::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
::::::
::::::Norm
::::::
::::::
::::::
:::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::::HI JOHN:
:::::::::
:::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::::::::
:::::::::WALTER-W2WIQ
:::::::::
:::::::::
::::::::
::::::::

::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::Sir John . . . .
::::::::
::::::::
::::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::::::::
::::::::
::::::::
::::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::::::::
::::::::
::::::::
::::::::
::::::::You say:
::::::::
::::::::
::::::::
::::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::::::::
::::::::
::::::::
::::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::::::::
::::::::
::::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::::::::up the overall RF gain to get the set working.
::::::::
::::::::
::::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::::::::
::::::::
::::::::OR
::::::::
::::::::
::::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::::::::
::::::::
::::::::You say:
::::::::
::::::::
::::::::
::::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::::::::
::::::::
::::::::
::::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::::::::
::::::::
::::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::::::::
::::::::
::::::::
::::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::::::::
::::::::
::::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::::::::
::::::::
::::::::
::::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::::::::
::::::::
::::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::::::::
::::::::
::::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::::::::
::::::::
::::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::::::::
::::::::
::::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::::::::
::::::::
::::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::::::::
::::::::
::::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::::::::
::::::::
::::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::::::::
::::::::
::::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::::::::
::::::::
::::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::::::::
::::::::
::::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::::::::
::::::::
::::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::::::::
::::::::
::::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::::::::
::::::::
::::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::::::::
::::::::
::::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::::::::
::::::::
::::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::::::::
::::::::
::::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::::::::
::::::::
::::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::::::::
::::::::
::::::::Re Review:
::::::::
::::::::
::::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::::::::
::::::::
::::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::::::::
::::::::
::::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::::::::
::::::::
::::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::::::::
::::::::
::::::::Thassittt . . .
::::::::
::::::::
::::::::
::::::::
::::::::Finally you say:
::::::::
::::::::
::::::::
::::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::::::::
::::::::
::::::::
::::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::::::::
::::::::
::::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::::::::
::::::::
::::::::Then fire up the set and evaluate your audio.
::::::::
::::::::
::::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::::::::
::::::::
::::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::::::::
::::::::
::::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::::::::
::::::::
::::::::
::::::::And that's the rest of the story . . . . .
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::Don't force it ! ! ! . . . . get a bigger hammer.
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::

::::::::
::::::::
::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::::::::
:::::::::
:::::::::
::::::::
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/10/2013 3:45:35 PMNorm Leal
That's pin #1 on a 47 tube.

Norm

:With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John
:
:
::John
::
:: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
::
:: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
::
:: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
::
::Norm
:::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
:::
:::
:::
:::
::::John
::::
:::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
::::
:::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
::::
::::Norm
::::
::::
::::
:::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
:::::
:::::
::::::John
::::::
:::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
::::::
::::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
::::::
::::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
::::::
::::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
::::::
::::::Norm
::::::
::::::
::::::
:::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:::::::
:::::::
:::::::
:::::::
:::::::
:::::::::HI JOHN:
:::::::::
:::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::::::::
:::::::::WALTER-W2WIQ
:::::::::
:::::::::
::::::::
::::::::

::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::Sir John . . . .
::::::::
::::::::
::::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::::::::
::::::::
::::::::
::::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::::::::
::::::::
::::::::
::::::::
::::::::You say:
::::::::
::::::::
::::::::
::::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::::::::
::::::::
::::::::
::::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::::::::
::::::::
::::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::::::::up the overall RF gain to get the set working.
::::::::
::::::::
::::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::::::::
::::::::
::::::::OR
::::::::
::::::::
::::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::::::::
::::::::
::::::::You say:
::::::::
::::::::
::::::::
::::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::::::::
::::::::
::::::::
::::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::::::::
::::::::
::::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::::::::
::::::::
::::::::
::::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::::::::
::::::::
::::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::::::::
::::::::
::::::::
::::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::::::::
::::::::
::::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::::::::
::::::::
::::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::::::::
::::::::
::::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::::::::
::::::::
::::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::::::::
::::::::
::::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::::::::
::::::::
::::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::::::::
::::::::
::::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::::::::
::::::::
::::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::::::::
::::::::
::::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::::::::
::::::::
::::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::::::::
::::::::
::::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::::::::
::::::::
::::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::::::::
::::::::
::::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::::::::
::::::::
::::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::::::::
::::::::
::::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::::::::
::::::::
::::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::::::::
::::::::
::::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::::::::
::::::::
::::::::Re Review:
::::::::
::::::::
::::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::::::::
::::::::
::::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::::::::
::::::::
::::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::::::::
::::::::
::::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::::::::
::::::::
::::::::Thassittt . . .
::::::::
::::::::
::::::::
::::::::
::::::::Finally you say:
::::::::
::::::::
::::::::
::::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::::::::
::::::::
::::::::
::::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::::::::
::::::::
::::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::::::::
::::::::
::::::::Then fire up the set and evaluate your audio.
::::::::
::::::::
::::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::::::::
::::::::
::::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::::::::
::::::::
::::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::::::::
::::::::
::::::::
::::::::And that's the rest of the story . . . . .
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::73's de Edd
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::Don't force it ! ! ! . . . . get a bigger hammer.
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::

::::::::
::::::::
::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
::::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::::::::
:::::::::
:::::::::
::::::::
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/11/2013 11:34:41 AMClifton
I may have missed it in all the posts, but has a known good speaker been tried connected to the radio. Possibly the voice coil is stuck.

Clifton


:That's pin #1 on a 47 tube.
:
:Norm
:
::With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John
::
::
:::John
:::
::: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
:::
::: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
:::
::: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
:::
:::Norm
::::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
::::
::::
::::
::::
:::::John
:::::
::::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
:::::
::::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
:::::
:::::Norm
:::::
:::::
:::::
::::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
::::::
::::::
:::::::John
:::::::
::::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
:::::::
:::::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
:::::::
:::::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
:::::::
:::::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
:::::::
:::::::Norm
:::::::
:::::::
:::::::
::::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
::::::::
::::::::
::::::::
::::::::
::::::::
::::::::::HI JOHN:
::::::::::
::::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
::::::::::
::::::::::WALTER-W2WIQ
::::::::::
::::::::::
:::::::::
:::::::::

:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::Sir John . . . .
:::::::::
:::::::::
:::::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
:::::::::
:::::::::
:::::::::
:::::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::You say:
:::::::::
:::::::::
:::::::::
:::::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
:::::::::
:::::::::
:::::::::
:::::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
:::::::::
:::::::::
:::::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:::::::::up the overall RF gain to get the set working.
:::::::::
:::::::::
:::::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
:::::::::
:::::::::
:::::::::OR
:::::::::
:::::::::
:::::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
:::::::::
:::::::::
:::::::::You say:
:::::::::
:::::::::
:::::::::
:::::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
:::::::::
:::::::::
:::::::::
:::::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
:::::::::
:::::::::
:::::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
:::::::::
:::::::::
:::::::::
:::::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
:::::::::
:::::::::
:::::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
:::::::::
:::::::::
:::::::::
:::::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
:::::::::
:::::::::
:::::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
:::::::::
:::::::::
:::::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
:::::::::
:::::::::
:::::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
:::::::::
:::::::::
:::::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
:::::::::
:::::::::
:::::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
:::::::::
:::::::::
:::::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
:::::::::
:::::::::
:::::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
:::::::::
:::::::::
:::::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
:::::::::
:::::::::
:::::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
:::::::::
:::::::::
:::::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:::::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
:::::::::
:::::::::
:::::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
:::::::::
:::::::::
:::::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
:::::::::
:::::::::
:::::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
:::::::::
:::::::::
:::::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
:::::::::
:::::::::
:::::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
:::::::::
:::::::::
:::::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
:::::::::
:::::::::
:::::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
:::::::::
:::::::::
:::::::::Re Review:
:::::::::
:::::::::
:::::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
:::::::::
:::::::::
:::::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
:::::::::
:::::::::
:::::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
:::::::::
:::::::::
:::::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
:::::::::
:::::::::
:::::::::Thassittt . . .
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::Finally you say:
:::::::::
:::::::::
:::::::::
:::::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
:::::::::
:::::::::
:::::::::
:::::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
:::::::::
:::::::::
:::::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
:::::::::
:::::::::
:::::::::Then fire up the set and evaluate your audio.
:::::::::
:::::::::
:::::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
:::::::::
:::::::::
:::::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
:::::::::
:::::::::
:::::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
:::::::::
:::::::::
:::::::::
:::::::::And that's the rest of the story . . . . .
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::73's de Edd
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::Don't force it ! ! ! . . . . get a bigger hammer.
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::

:::::::::
:::::::::
:::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
:::::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
:::::::::::
::::::::::
::::::::::
:::::::::
:::::::::
::::::::
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/12/2013 2:46:41 PMJohn
The 250 ohm resistor in the power supply is not open. You might be right about the speaker and have not subbed one yet. Sounds a bit like it rattles and the set gives a big crackling sound when you turn the tuner. John


:I may have missed it in all the posts, but has a known good speaker been tried connected to the radio. Possibly the voice coil is stuck.
:
:Clifton
:
:
::That's pin #1 on a 47 tube.
::
::Norm
::
:::With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John
:::
:::
::::John
::::
:::: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
::::
:::: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
::::
:::: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
::::
::::Norm
:::::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
:::::
:::::
:::::
:::::
::::::John
::::::
:::::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
::::::
:::::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
::::::
::::::Norm
::::::
::::::
::::::
:::::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
:::::::
:::::::
::::::::John
::::::::
:::::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
::::::::
::::::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
::::::::
::::::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
::::::::
::::::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
::::::::
::::::::Norm
::::::::
::::::::
::::::::
:::::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::
:::::::::::HI JOHN:
:::::::::::
:::::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
:::::::::::
:::::::::::WALTER-W2WIQ
:::::::::::
:::::::::::
::::::::::
::::::::::

::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::Sir John . . . .
::::::::::
::::::::::
::::::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
::::::::::
::::::::::
::::::::::
::::::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::You say:
::::::::::
::::::::::
::::::::::
::::::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
::::::::::
::::::::::
::::::::::
::::::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
::::::::::
::::::::::
::::::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
::::::::::up the overall RF gain to get the set working.
::::::::::
::::::::::
::::::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
::::::::::
::::::::::
::::::::::OR
::::::::::
::::::::::
::::::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
::::::::::
::::::::::
::::::::::You say:
::::::::::
::::::::::
::::::::::
::::::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
::::::::::
::::::::::
::::::::::
::::::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
::::::::::
::::::::::
::::::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
::::::::::
::::::::::
::::::::::
::::::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
::::::::::
::::::::::
::::::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
::::::::::
::::::::::
::::::::::
::::::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
::::::::::
::::::::::
::::::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
::::::::::
::::::::::
::::::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
::::::::::
::::::::::
::::::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
::::::::::
::::::::::
::::::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
::::::::::
::::::::::
::::::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
::::::::::
::::::::::
::::::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
::::::::::
::::::::::
::::::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
::::::::::
::::::::::
::::::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
::::::::::
::::::::::
::::::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
::::::::::
::::::::::
::::::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
::::::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
::::::::::
::::::::::
::::::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
::::::::::
::::::::::
::::::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
::::::::::
::::::::::
::::::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
::::::::::
::::::::::
::::::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
::::::::::
::::::::::
::::::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
::::::::::
::::::::::
::::::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
::::::::::
::::::::::
::::::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
::::::::::
::::::::::
::::::::::Re Review:
::::::::::
::::::::::
::::::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
::::::::::
::::::::::
::::::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
::::::::::
::::::::::
::::::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
::::::::::
::::::::::
::::::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
::::::::::
::::::::::
::::::::::Thassittt . . .
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::Finally you say:
::::::::::
::::::::::
::::::::::
::::::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
::::::::::
::::::::::
::::::::::
::::::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
::::::::::
::::::::::
::::::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
::::::::::
::::::::::
::::::::::Then fire up the set and evaluate your audio.
::::::::::
::::::::::
::::::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
::::::::::
::::::::::
::::::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
::::::::::
::::::::::
::::::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
::::::::::
::::::::::
::::::::::
::::::::::And that's the rest of the story . . . . .
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::73's de Edd
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::Don't force it ! ! ! . . . . get a bigger hammer.
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::
::::::::::

::::::::::
::::::::::
::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
:::::::::::
::::::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
::::::::::::
:::::::::::
:::::::::::
::::::::::
::::::::::
:::::::::
:::::::::
::::::::
::::::::
:::::::
:::::::
::::::
::::::
:::::
:::::
::::
::::
:::
:::
::
::
:
:

1/14/2013 10:24:51 AMClifton
If the radio makes a crackling/static sound when rotating the tuning capacitor, then possibly the plates are shorting from dust or whatever. It is also possible the grounding contacts between the rotor shaft and the capacitor frame may need to be cleaned and relubed.

Clifton


:The 250 ohm resistor in the power supply is not open. You might be right about the speaker and have not subbed one yet. Sounds a bit like it rattles and the set gives a big crackling sound when you turn the tuner. John
:
:
::I may have missed it in all the posts, but has a known good speaker been tried connected to the radio. Possibly the voice coil is stuck.
::
::Clifton
::
::
:::That's pin #1 on a 47 tube.
:::
:::Norm
:::
::::With both 47's in place I can hear a station but not loud and quite fuzzy plus at zero volume there is some hum and buzzing. If I take out either 47 I can hear a station clearly but not loud. John
::::
::::
:::::John
:::::
::::: Both legs of primary of an output transformer should be close in resistance but not the same. Outside winding will have higher resistance due to longer length of wire.
:::::
::::: Even if 1/2 was open you would still hear radio. The circuit is push-pull.
:::::
::::: Do you have anything out of the speasker, hum? Do you hear a click when pulling the 27 tube?
:::::
:::::Norm
::::::I tried putting the antennna on the grid of the 27 and still no change. The plate voltage on the 27 is 80volts. I still think both legs of the primary on the audio output transformer should be about the same resistance. John
::::::
::::::
::::::
::::::
:::::::John
:::::::
::::::: Primary of the audio output transformer should read in the couple hundred ohm range. Secondary just a couple ohms. The secondary wouldn't be open but may have a bad connection? This is the transformer connected to plates of the 47 tubes.
:::::::
::::::: Do you hear any noise out of the speaker? Can you hear any signals with an antenna connected to pin #3 of the 27, detector/audio amplifier? Be sure pin #2 on the 27 has a positive voltage, around 100.
:::::::
:::::::Norm
:::::::
:::::::
:::::::
::::::::I think I found the problem. Not sure if this is the problem but the only thing I could find wrong with the radio is the audio output transformer. One side of the input measures 239 ohms and the other side measures 505 ohms. Seems like they should measure closer to the same value. John
::::::::
::::::::
:::::::::John
:::::::::
::::::::: Jackson Bell 96 is a TRF radio. The 24 tubes amplify the RF signal and are tetrode types. These tubes need positive screen voltage but mush less than plate. Important to have positive plate voltage (pin #2), around 200 volts. Expect screen to be 100 volts or less.
:::::::::
:::::::::With volume turned up cathode (pin #4) should be around 3 volts. If not may be a problem with volume control or 300 ohm series resistor.
:::::::::
:::::::::With a TRF radio you can move the antenna to a different tuner. Antenna could be connected to pin #3 of the 27. This will bypass the two 24 tubes.
:::::::::
:::::::::http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf
:::::::::
:::::::::Norm
:::::::::
:::::::::
:::::::::
::::::::::Hi Edd, Thanks for your reply. You asked about the 250k resistor between the screen and cathode of the first rf. It is NOT there. Also, the 10k resistor feeding the primary of the output transformer for the 27 is not there. I measured B+ at 272v and the screen voltage on the first rf tube was 125v. Wouldn't this make for too much screen current?
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::::::::::::HI JOHN:
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::::::::::::SOUNDS AND LOOKS LIKE SOMEBODY DID A LOT OF CHANGES.NONE OF THAT JIVES WITH THE SCHEMATIC-RIDERS VOL.5 PAGE 2.LOOKS LIKE YOU WILL HAVE TO REWIRE AS PER THE SCHEMATIC WITH THE PROPER RESISTOS.
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::::::::::::WALTER-W2WIQ
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:::::::::::Sir John . . . .
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:::::::::::Considering that you are consulting this schematic . . . . . http://www.nostalgiaair.org/PagesByModel/680/M0009680.pdf.
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:::::::::::(And that you have a moderately healthy length of aerial wire being connected to the set.)
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:::::::::::You say:
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:::::::::::It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor.
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:::::::::::In that respect, is that possibly, someone prior might have been diddling around with parts values in order to try to get reception..
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:::::::::::That 50 K value is getting a heftier screen voltage supplied to the RF pairs screens, and that he might have thought that would heft
:::::::::::up the overall RF gain to get the set working.
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:::::::::::Then the SELECTED 150 K to ground would be creating a voltage divider bridge with use of those two resistor values, giving a desired trimmed in screen voltage value.
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:::::::::::Did he read the adjunt 50 K grid leak resistor numbering and think THAT was supposed to be the value of the screen voltage dropping resistor ?
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:::::::::::You say:
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:::::::::::Also, from the screen of the 1st 24 to ground is a .5 capacitor.
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:::::::::::That would be functioning as a screen grid bypassing / decoupling function, and I could see no fault with that . . .just look above at the 86 chassis and you will see its utilization on the sets frontal RF amp stage.
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:::::::::::As low as an .05 ufd value is usually adequate , with .5 being a bit overkill.
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:::::::::::Now, I would like to know the current status / presence of the 250K resistor between the screen of the frontal RF stage and its cathode.
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:::::::::::Is it NOT even being there ? . . . . and just the presence of the prior mentioned 150 K to ground from the screens supply ?
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:::::::::::Let me 'splains to you just how this older type of " volume control " action functions on these older TRF sets.
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:::::::::::Assuredly you are more familiar with the newer technique where the volume control is being a variable AC voltage divider bridge between an audio preamp stage and the 1st grid of the AF output stage.
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:::::::::::On this TRF set, take note of the 20K "volume" pot and the grounding of its center wiper, on its left resistance connector note that it is connected to the aerial /antenna input for the set.
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:::::::::::Also, be aware that the proportional counter clockwise rotational direction of the "volume" pot will be placing the grounded wiper ever closer to that terminal.
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:::::::::::Sooooooo you could now see that antenna signal eventually getting shorted out when at max CCW.
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:::::::::::But thats not ALL of the story . . . . .there is a dual action being present . . . . . now go back to the schematic and note that the screens are getting their operating supply voltage via the 150 K supply resistor and additionally there is another 250k resistor that feeds a counterpoise + bias voltage over to the paired /shared cathodes of the 24 frontal RF stages.
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:::::::::::So here is the somewhat subliminal OTHER situation / effect, which was occuring when the vol control was being at its max CCW position (minimum volume).
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:::::::::::The screen voltage supply from the 150 K supply resistor feds into the pair of RF screens and they in turn connect to the 300 ohm resistor in series to the path of the other end terminal of the 20 K pot.
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:::::::::::You ask . . .What is dat dere 300 ohm resistor in dere for ?
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:::::::::::Its serving as an " electrical stop " for the mechanical range of the 20 K pot, in that controls max (volume) CW position so that there is a 300 ohm cathode resistor presence, instead of the dead short to ground of the RF tubes cathodes, that the wiper would otherwise have created .
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:::::::::::Soooooo if we have the screen voltage supply voltage, being fed in from the 150 K screen resistor and it feeding the screens and additionally feeding thru a 250 K resistor to the cathode pairs of the RF amps and then it passes on to the series 300 ohm resistor and then into the
:::::::::::20 k pot which would have its wiper at the other end, with there then being the full 20K presence of resistance across the control before its getting to the wipers ground.
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:::::::::::That would be a voltage divider bridge being made with the 250K / 300+20K pair, or about a 1/10 division down of the + screen voltage .
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:::::::::::On various sets designs, I have seen them working with ~ 85-----125 volts being on the RF tube(s) screen(s), so with that divisional ratio, expect 8.5 -12 VDC being counterpoise biased to the RF cathodes.
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:::::::::::That will then be squelching the gain capabilities of those frontal RF tubes severely.
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:::::::::::Now . . . . . start turning the volume control clockwise and you can figure that the "short" across the antenna, for RF attenuation, will dissappear quite QUICKLY, with that being a 20K pot. (Now if it was a 25 ohm pot that would be a different story, within its degrees of rotation ! )
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:::::::::::But the rotated grounded wiper is now starting to decrease the value of that pots resistance from its effectively being an extended 20K or so of "cathode resistor".
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:::::::::::As the wiper gets ever closer to the 300 ohm fixed resistor, the RF gain will be increasing, along with the shifting voltage divider ratio being negated, such that the counterpoise + voltage is being proportionatively decreased. At one point, the counterpoise voltage is balanced out and negated , and the gain is then dependent upon the final low series resistance of the 20 K pot and that 300 ohm series resistor.
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:::::::::::So that's the low down on this TRF sets type of "Volume control" . . . . . via RF gain control.
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:::::::::::Re Review:
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:::::::::::(Tell them what you're gonna TELL them . . . .TELL THEM ! . . . .Re Tell them what you have done TOLD them.)
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:::::::::::A Max CCW of the 20 K pot is shorting out the RF aerial input to ground via its wiper.
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:::::::::::Simultaneously a counterpoise +biasing voltage is being applied to the cathodes of the RF tube cathodes and electronically supressing RF gain of those stages.
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:::::::::::With a progressive rotation of that volume control wiper in its CW direction, the RF "Short" disappears rapidly in its initial degree of rotation, WHILE the series resistance of the pot back towards the counterpoise bias voltage is now proportionally decreasing.
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:::::::::::That is letting the RF stages gains increase in the same manner. By the time the 20K control is at max CW, the set is operating at max gain with a 300 ohm cathode resistor for the RF stages and the counterpoise, gain supressing biasing, being completely negated.
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:::::::::::Thassittt . . .
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:::::::::::Finally you say:
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:::::::::::Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia
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:::::::::::No biggie on that . . . its relevant to the grid leak detector scheme of this sets 27 toobie.
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:::::::::::If you want to 'speriments . . . . put in a 39K in series with a 10 K, with the 10 K being on the grounded end.
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:::::::::::Then fire up the set and evaluate your audio.
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:::::::::::With that series configuration, you can then lever the blade of a mini screwdriver from ground to shorting out that resistor junction.
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:::::::::::That will short out the 10 K and let you then critically evaluate the sets detected audio with either a 40 or 50 K resistor being in circuit . . . . RAPIDLY !
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:::::::::::The time constant of its companion shunting capacitors time constant should favor bass with the 50K value or more treble at 40/39 K. value.
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:::::::::::And that's the rest of the story . . . . .
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:::::::::::73's de Edd
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:::::::::::Don't force it ! ! ! . . . . get a bigger hammer.
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:::::::::::::I have this JacksonBell model 96 and it does not work. Gets one station a little bit but the sound is fuzzy. It has a 50K ohm resistor feeding the screens of the 24's and from the screen of the second 24 to ground is a 150K resistor. Also, from the screen of the 1st 24 to ground is a .5 capacitor. This is not quite the same as the schematic. Why? Tube layout is the same as a 96 but some parts are different. Also, from the cathode of the 27 to ground is a 40k ohm resistor instead of a 50k as shown on the dia. I have checked tubes and changed filter caps.
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