O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
Referencing:
Standing by for feedback.....
73's de Edd
:Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
CC
:
:
:
:O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
:
:
:When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
:
:
:Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
:
:
:
:There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
:
:A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
:
:Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
:
:
:Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
:
:Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
:
:Referencing:
:
:
:
:
:Standing by for feedback.....
:
:
:
:73's de Edd
:
:
:
:
:
:
:
:
::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
With no negative voltage on pin #5 of you 6J5 the oscillator isn't operating. Did you check continuity of the oscillator coil & band switch?
The 6L7 won't have negative voltage either when 6J5 isn't supplying it. Work on getting your 6J5 oscillator operating.
Resistors will not be the problem stopping your oscillator.
Norm
:With respect to Walt's initial comments, while I don't have capacitance measurement capability, I find that C4 is definitely not shorted. I measured tube pin voltages and compared them with a table from page 8-42 of the Riders (socket voltages for 1204). As an example, I Find:
:1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
:2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
:
:There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
:
:Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
:
:CC
:
::
::
::
::O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
::
::
::When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
::
::
::Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
::
::
::
::There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
::
::A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
::
::Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
::
::
::Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
::
::Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
::
::Referencing:
::
::
::
::
::Standing by for feedback.....
::
::
::
::73's de Edd
::
::
::
::
::
::
::
::
:::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
Per Norm's suggestion, I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). Coil K and N (Short wave / Police band) both have continuity to the C1/C4 junction.
Having found this, I was looking for a way to get to the coil, but it appears to be major invasive surgery. Unscrewing the two nuts on the top of the can reveal that the coil stack studs are soldered to the metal can itself. Therefore, it appears that I would have to disconnect all connections to the oscillator coil stack (K,N,F) from the bottom side, remove the entire metal can / coil assy, and then try to remove the coil from the can by unsoldering it. After this, it looks like the coils are waxed onto the paper tube?
Might there be an easier way to access the F coil? Or is there a way to bypass it with a new coil? If so, does anyone know what inductance value it is?
I'm starting to realize why the last owner may have set this one out to pasture...
Thanks,
CC
:Hi CC
:
: With no negative voltage on pin #5 of you 6J5 the oscillator isn't operating. Did you check continuity of the oscillator coil & band switch?
:
: The 6L7 won't have negative voltage either when 6J5 isn't supplying it. Work on getting your 6J5 oscillator operating.
:
: Resistors will not be the problem stopping your oscillator.
:
:Norm
:
::With respect to Walt's initial comments, while I don't have capacitance measurement capability, I find that C4 is definitely not shorted. I measured tube pin voltages and compared them with a table from page 8-42 of the Riders (socket voltages for 1204). As an example, I Find:
::1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
::2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
::
::There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
::
::Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
::
::CC
::
:::
:::
:::
:::O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
:::
:::
:::When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
:::
:::
:::Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
:::
:::
:::
:::There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
:::
:::A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
:::
:::Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
:::
:::
:::Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
:::
:::Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
:::
:::Referencing:
:::
:::
:::
:::
:::Standing by for feedback.....
:::
:::
:::
:::73's de Edd
:::
:::
:::
:::
:::
:::
:::
:::
::::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
That's the tuned winding so number of turns are critical for proper alignment. Can you see a wire disconnected?
http://www.nostalgiaair.org/PagesByModel/712/M0024712.pdf
Might look through this list for a replacement.
http://www.oldradioparts.com/2a6fla.txt
You can buy an universal broadcast band coil but not right for this radio. You also have short wave bands.
Norm
:Norm & All,
:
:Per Norm's suggestion, I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). Coil K and N (Short wave / Police band) both have continuity to the C1/C4 junction.
:
:Having found this, I was looking for a way to get to the coil, but it appears to be major invasive surgery. Unscrewing the two nuts on the top of the can reveal that the coil stack studs are soldered to the metal can itself. Therefore, it appears that I would have to disconnect all connections to the oscillator coil stack (K,N,F) from the bottom side, remove the entire metal can / coil assy, and then try to remove the coil from the can by unsoldering it. After this, it looks like the coils are waxed onto the paper tube?
:
:Might there be an easier way to access the F coil? Or is there a way to bypass it with a new coil? If so, does anyone know what inductance value it is?
:
:I'm starting to realize why the last owner may have set this one out to pasture...
:
:Thanks,
:
:CC
:
::Hi CC
::
:: With no negative voltage on pin #5 of you 6J5 the oscillator isn't operating. Did you check continuity of the oscillator coil & band switch?
::
:: The 6L7 won't have negative voltage either when 6J5 isn't supplying it. Work on getting your 6J5 oscillator operating.
::
:: Resistors will not be the problem stopping your oscillator.
::
::Norm
::
:::With respect to Walt's initial comments, while I don't have capacitance measurement capability, I find that C4 is definitely not shorted. I measured tube pin voltages and compared them with a table from page 8-42 of the Riders (socket voltages for 1204). As an example, I Find:
:::1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
:::2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
:::
:::There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
:::
:::Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
:::
:::CC
:::
::::
::::
::::
::::O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
::::
::::
::::When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
::::
::::
::::Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
::::
::::
::::
::::There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
::::
::::A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
::::
::::Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
::::
::::
::::Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
::::
::::Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
::::
::::Referencing:
::::
::::
::::
::::
::::Standing by for feedback.....
::::
::::
::::
::::73's de Edd
::::
::::
::::
::::
::::
::::
::::
::::
:::::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
“ I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). ”
…and that was my specified ---green marked up--- BCB osc coil winding on the thumbnail, and I did not know at that time of the condition of the band switch, but you confirmed its connectivity in that band position, but with the BCB osc coil section being "open".
I hope, and certainly feel that the coils start or end winding wire that goes over to the adjunct companion terminal lug of the coil will probably be open very near to that terminal position , that usually being due to a conformal coating aging with time and progressive pulling strain on the encased wire simultaneously and snapping it, or sometimes a sloppy factory joint or Rosin erosion
Heck…viewed under a jewelers eye loupe or higher powered magnifying glass you might even be able to see a bit of tell tale blue/green…CuSo4.. residue showing at the break point.
My usual procedure..in such a quandry…is to take an ohmmeter and initially connect into one of those two contact terminals that you can definitely ascertain as physically routed and going to a specific inner wire …(start of the winding)…or the outermost wire (end of the winding).
Then you go to the opposite terminal about half way or so between its wire connection and the coil winding and take a single edged razor blade….the one that has a massive amount of good aluminum metal shrouding the blade proper… then you press the free ohmmeter probe in contact with that blades aluminum and make a very, very slight lateral scrape upon the wire to see if there is continuity.(Or if you cannot see your scrape, you can temporarily, move the distant ohmmeter connection to the nearby terminal, thus confirming within that ½ in or so distance that you actually had penetrated the insulation)…then you move the connection back across the coil, now fully knowing that your razor blade can make good contact.
That test would let you then know that the whole winding proper is intact and you need to make an external repair onto the short piece of wire exposed from the coil proper over to its companion terminal lug.
If that wire happens to be enamel or even Formvar, it’s a piece of cake to do a micro scrape to make ohmic contact through, but, if cotton covered you need to make multiple fraying scrapes to expose downwards into the enameled wire…or Litz .
If no continuity was found, reverse procedure to the other terminal involved and work on exposing the other wire and checking for its continuity at one point .
I very rarely suspect an inner winding failure, since these oscillator coil functions are relatively void of any significant voltage level and power level whatsoever. Its not like an inductive element being utilized in a plate circuitry design , where hundreds of volts might be across a coil as well as multi-milliamperes of current consumption.
If you do find the open, you might ask for my repair technique on that wisp of fine wire exposed…as its usually a one or two shot attempt at its successful repair with the short length of winding wire exposed…or none if you happen to have palsy twitches…lol.
And you just don’t typically find exotic replacement osc coils such as you have.
73's de Edd
:CC Rider
:
: That's the tuned winding so number of turns are critical for proper alignment. Can you see a wire disconnected?
:
:http://www.nostalgiaair.org/PagesByModel/712/M0024712.pdf
:
: Might look through this list for a replacement.
:
:http://www.oldradioparts.com/2a6fla.txt
:
: You can buy an universal broadcast band coil but not right for this radio. You also have short wave bands.
:
:Norm
:
:
::Norm & All,
::
::Per Norm's suggestion, I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). Coil K and N (Short wave / Police band) both have continuity to the C1/C4 junction.
::
::Having found this, I was looking for a way to get to the coil, but it appears to be major invasive surgery. Unscrewing the two nuts on the top of the can reveal that the coil stack studs are soldered to the metal can itself. Therefore, it appears that I would have to disconnect all connections to the oscillator coil stack (K,N,F) from the bottom side, remove the entire metal can / coil assy, and then try to remove the coil from the can by unsoldering it. After this, it looks like the coils are waxed onto the paper tube?
::
::Might there be an easier way to access the F coil? Or is there a way to bypass it with a new coil? If so, does anyone know what inductance value it is?
::
::I'm starting to realize why the last owner may have set this one out to pasture...
::
::Thanks,
::
::CC
::
:::Hi CC
:::
::: With no negative voltage on pin #5 of you 6J5 the oscillator isn't operating. Did you check continuity of the oscillator coil & band switch?
:::
::: The 6L7 won't have negative voltage either when 6J5 isn't supplying it. Work on getting your 6J5 oscillator operating.
:::
::: Resistors will not be the problem stopping your oscillator.
:::
:::Norm
:::
::::With respect to Walt's initial comments, while I don't have capacitance measurement capability, I find that C4 is definitely not shorted. I measured tube pin voltages and compared them with a table from page 8-42 of the Riders (socket voltages for 1204). As an example, I Find:
::::1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
::::2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
::::
::::There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
::::
::::Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
::::
::::CC
::::
:::::
:::::
:::::
:::::O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
:::::
:::::
:::::When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
:::::
:::::
:::::Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
:::::
:::::
:::::
:::::There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
:::::
:::::A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
:::::
:::::Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
:::::
:::::
:::::Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
:::::
:::::Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
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:::::Referencing:
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:::::Standing by for feedback.....
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:::::73's de Edd
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::::::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.
I thank everyone again for your inputs. I believe you have been able to point me in the right direction.
CC
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:“ I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). ”
:…and that was my specified ---green marked up--- BCB osc coil winding on the thumbnail, and I did not know at that time of the condition of the band switch, but you confirmed its connectivity in that band position, but with the BCB osc coil section being "open".
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:I hope, and certainly feel that the coils start or end winding wire that goes over to the adjunct companion terminal lug of the coil will probably be open very near to that terminal position , that usually being due to a conformal coating aging with time and progressive pulling strain on the encased wire simultaneously and snapping it, or sometimes a sloppy factory joint or Rosin erosion
:
:Heck…viewed under a jewelers eye loupe or higher powered magnifying glass you might even be able to see a bit of tell tale blue/green…CuSo4.. residue showing at the break point.
:
:My usual procedure..in such a quandry…is to take an ohmmeter and initially connect into one of those two contact terminals that you can definitely ascertain as physically routed and going to a specific inner wire …(start of the winding)…or the outermost wire (end of the winding).
:
:Then you go to the opposite terminal about half way or so between its wire connection and the coil winding and take a single edged razor blade….the one that has a massive amount of good aluminum metal shrouding the blade proper… then you press the free ohmmeter probe in contact with that blades aluminum and make a very, very slight lateral scrape upon the wire to see if there is continuity.(Or if you cannot see your scrape, you can temporarily, move the distant ohmmeter connection to the nearby terminal, thus confirming within that ½ in or so distance that you actually had penetrated the insulation)…then you move the connection back across the coil, now fully knowing that your razor blade can make good contact.
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:That test would let you then know that the whole winding proper is intact and you need to make an external repair onto the short piece of wire exposed from the coil proper over to its companion terminal lug.
:
:If that wire happens to be enamel or even Formvar, it’s a piece of cake to do a micro scrape to make ohmic contact through, but, if cotton covered you need to make multiple fraying scrapes to expose downwards into the enameled wire…or Litz .
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:If no continuity was found, reverse procedure to the other terminal involved and work on exposing the other wire and checking for its continuity at one point .
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:I very rarely suspect an inner winding failure, since these oscillator coil functions are relatively void of any significant voltage level and power level whatsoever. Its not like an inductive element being utilized in a plate circuitry design , where hundreds of volts might be across a coil as well as multi-milliamperes of current consumption.
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:If you do find the open, you might ask for my repair technique on that wisp of fine wire exposed…as its usually a one or two shot attempt at its successful repair with the short length of winding wire exposed…or none if you happen to have palsy twitches…lol.
: And you just don’t typically find exotic replacement osc coils such as you have.
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:73's de Edd
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::CC Rider
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:: That's the tuned winding so number of turns are critical for proper alignment. Can you see a wire disconnected?
::
::http://www.nostalgiaair.org/PagesByModel/712/M0024712.pdf
::
:: Might look through this list for a replacement.
::
::http://www.oldradioparts.com/2a6fla.txt
::
:: You can buy an universal broadcast band coil but not right for this radio. You also have short wave bands.
::
::Norm
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::
:::Norm & All,
:::
:::Per Norm's suggestion, I checked continuity on the Broadcast Oscillator coil (F on schematic) and find that it indeed appears to be open (I measured between C4/C1 junction and the band switch - the band switch continuity checks out fine). Coil K and N (Short wave / Police band) both have continuity to the C1/C4 junction.
:::
:::Having found this, I was looking for a way to get to the coil, but it appears to be major invasive surgery. Unscrewing the two nuts on the top of the can reveal that the coil stack studs are soldered to the metal can itself. Therefore, it appears that I would have to disconnect all connections to the oscillator coil stack (K,N,F) from the bottom side, remove the entire metal can / coil assy, and then try to remove the coil from the can by unsoldering it. After this, it looks like the coils are waxed onto the paper tube?
:::
:::Might there be an easier way to access the F coil? Or is there a way to bypass it with a new coil? If so, does anyone know what inductance value it is?
:::
:::I'm starting to realize why the last owner may have set this one out to pasture...
:::
:::Thanks,
:::
:::CC
:::
::::Hi CC
::::
:::: With no negative voltage on pin #5 of you 6J5 the oscillator isn't operating. Did you check continuity of the oscillator coil & band switch?
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:::: The 6L7 won't have negative voltage either when 6J5 isn't supplying it. Work on getting your 6J5 oscillator operating.
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:::: Resistors will not be the problem stopping your oscillator.
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::::Norm
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:::::With respect to Walt's initial comments, while I don't have capacitance measurement capability, I find that C4 is definitely not shorted. I measured tube pin voltages and compared them with a table from page 8-42 of the Riders (socket voltages for 1204). As an example, I Find:
:::::1. 6K7 RF/6L7 DET, pin 3(plate)=270V vs. 246V, pin 4(grid)=126V vs. 83V. On 6L7 pin 5(grid)= 0V vs. -10V.
:::::2. 6J5 OSC, pin 3(plate)=83V vs. 121V, pin 5(grid)=0 vs. -10.5V.
:::::
:::::There appears to be a similar trend for the remaining tubes in that the voltages I measure are not matching those in Riders exactly. For some like the 6J5 audio section, I seem to get 0V instead of -2V on the grids. Are these voltage differences significant? If so, might they be caused by drifting resistors?
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:::::Based on Edd's comments, I've got some more homework to do. Thanks for all the feedback thus far. Stay tuned.
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:::::CC
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::::::O.K....now.... considering that all is working normal on the Shortwave aspects seems like all portions or the receiver...e.g. the RF amp---Mixer---Local osc--- IF strip----detection and the AF group are collectively working in those two SW freq bands.
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::::::When it comes to the Broadcast ONLY not working; you might consider a bandswitch contacts action issue or the [green marked up] area on the enclosed thumbnail schema (open or broken coil wire) and its tie in to the osc band switching portion of the switch that is shown just below it. (E.G. a possible open on that green section marked osc coil for the BC band, also be sure to check the value of the local oscillators grid resistor... R5... and confirm that it has not drifted off value with time.
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::::::Also, with the general nature of the types of capacitors used in this unit ...along with their inherent reliability and trouble free nature.... hopefully none of them have been touched in a "massive" capacitor replacement campaign. Thereby there would not be a chance of a mis-wire or improper selected component type in the process of replacement...with nothing even having been touched in that area.
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::::::There also might be the same coil or bandswitch contact issue in the RF amp and mixer input grids section of the RF front end.
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::::::A possible quick work around / bypassing evaluation of that area might be accomplished by the connection of a loose wire aerial wire made from ~ 10 feet of hook up wire, with it then being connected to the mixers first RF in grid (pin # 5) as I have shown marked in at the very top of the schema.....that would be pin # 5. If BCB reception is then present, explore the aforementioned RF components and RF section bandswitching action integrity in the sets RF front end.
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::::::Lastly.....on the timely LF bursts "blip-blips" present ,confirm all specified tubes having their shields if so required, as well as the positive grounding action of their asssociated pressure contacts.
::::::
::::::
::::::Also look at the very top of the schema where you see a B+ supply line sequentially running across feeding the RF --- DET/MIXER --- IF AMP screen grids. The bypassing of the whole string is dependent upon the I.F. tubes RF B+ bypassing capacitor.
::::::
::::::Take a very short leaded disc ceramic cap .01---.1 ufd ufd and go to each tube and hold / touch from screen grid to adjunct chassis ground to see if the "blip-blip" noise ceases.
::::::
::::::Referencing:
::::::
::::::
::::::
::::::
::::::Standing by for feedback.....
::::::
::::::
::::::
::::::73's de Edd
::::::
::::::
::::::
::::::
::::::
::::::
::::::
::::::
:::::::Sounds like it's 'motorboating'(in oscillation). Has C4 been checked? Does touching various terminals with a voltmeter probe change the sound at all? (Some digital multimeters may introduce their own internal noise to the circuit). That might help to locate the area of concern. An idea of expected RF/IF tube pin voltages may help,an RF/IF amplifier stage can easily be driven into oscillation by wrong voltages. Maybe list and compare the pin voltages you see on the broadcast band to the voltages you see on those same pins in the shortwave position? A generic troubleshooting chart for 'motorboating'may also help in giving you a plan to follow for locating the concern. Let us know what you find.