R6 I found as a 470k to ground ... but the print says it should be a 330k connecting to R1 at the mixer osc coil connection??
Why?
I rewired it that way but the longer wire to R1 causes a de-tuning of the osc.
I think I'll just put a 470k to grnd... but why is this shown like that??
Also R9 (18 ohm) is supplying AC for the Plate of the 35z5 rectifier instead of the lamp tap... strange.
The print also shows R8 as 22k... but maybe they mean 2.2k?
There is a 1.8k 4watt there now.
Peter:
It looks like to me that they are using the negative grid Voltage on the oscillator tube to bias the grid of the audio output. Strange, to say the least. As for the 35Z5, I guess the designer had a brother in law who sold rectifer tubes, for as far as I know, that arrangement would make for a shortened life for the 35Z5. The cathode resistor for the 50L6 seems a little smaller than usual, and your Wattage values seem a little large, to say the least. I haven't had my coffee yet, this might make more sense when all my brain cells have had their morning caffiene.
Lewis L.
P. S. As for R8, check the screen Voltage of the 50L6, if it is a lot lower than the plate, go for the 2.2K instead of the 22K. That looks a little funny to me, too.
Lewis
I could see using bias from the oscillator but they also have a cathode resistor, R7 - 150 ohms, for the 50L6. If this resistor is really in the circuit you can ground the 470K grid resistor. The grid has bias by using a cathode resistor. Value is reasonable for a 50L6.
Doubt if the lamp and 35Z5 are really wired that way? The lamp is across a section of 35Z5 filament but plate current isn't being drawn through the circuit. This will make the lamp very dim.
Norm
:::Hey Norm or Thomas or whoever:
:::I'm comparing this Schem to the actual circuit and find funny difs.
:::http://www.nostalgiaair.org/PagesByModel/459/M0000459.pdf
:::
:::R6 I found as a 470k to ground ... but the print says it should be a 330k connecting to R1 at the mixer osc coil connection??
:::Why?
:::I rewired it that way but the longer wire to R1 causes a de-tuning of the osc.
:::I think I'll just put a 470k to grnd... but why is this shown like that??
:::
:::Also R9 (18 ohm) is supplying AC for the Plate of the 35z5 rectifier instead of the lamp tap... strange.
:::
:::The print also shows R8 as 22k... but maybe they mean 2.2k?
:::There is a 1.8k 4watt there now.
:::
::
::
::Peter:
::It looks like to me that they are using the negative grid Voltage on the oscillator tube to bias the grid of the audio output. Strange, to say the least. As for the 35Z5, I guess the designer had a brother in law who sold rectifer tubes, for as far as I know, that arrangement would make for a shortened life for the 35Z5. The cathode resistor for the 50L6 seems a little smaller than usual, and your Wattage values seem a little large, to say the least. I haven't had my coffee yet, this might make more sense when all my brain cells have had their morning caffiene.
::
::Lewis L.
:
:P. S. As for R8, check the screen Voltage of the 50L6, if it is a lot lower than the plate, go for the 2.2K instead of the 22K. That looks a little funny to me, too.
:
:Lewis
I will agree that this schematis has some oddball things going on in it. Maybe the designer wanted his AA5 design to be different or maybe he was an early user of things that are illegal to obtain today. As I said, I predict a short life for the rectifier tube, and I am also at a total loss to expalin the why of the 50L6 biasing arrangement.
Lewis
Yes Norm the 150 ohm cathode resistor is in there.
So..I have chosen to replace the oscillator biased 330k R6 with a more conventional 430k directly to ground.
I also decided to remove R9 the 18 ohm resistor to the 35Z5 plate and connected the plate to the lamp tap for a much nicer brighter lamp now.
I've concluded that R8 must have been meant to be written as 2.2k not 22k which would only serve to severely reduce the B+ I'm sure. There is actually a 1.8k in there now.
Thanks guys... BTW..If you are curious...
You can see this (now beautiful-looking) little radio up on Ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=009&sspagename=STRK%3AMESE%3AIT&viewitem=&item=190111992392&rd=1&rd=1
As for the 50L6 cathode resistor, 150 ohms is standard for this tube in this circuit with these voltages. I don't recall the last time I saw another value. Every 50L6, 50C5, 35L6, 25L6, and what-not on a 120 volt AC/DC circuit that I've ever seen has had a 150 ohm resistor for bias, unless bias was obtained by other means.
The oscillator trick will provide extra bias. The thing I wonder about, though, is that the bias would change over the dial (since oscillator voltage changes over the dial). I have seen this trick used before in battery receivers, where it was undesirable to provide bias via dropping resistors (wasted power).
T.
As I recall, it has something to do with unequal warming of the filaments when the radio is first turned on, and the hot filament current being lower than the cold filament current, and the B+ current not flowing until the smaller tubes start heating and drawing current, then part of the rectifier tube filament is lit with DC.
Having the rectifier wired as per the schematic has less current flowing through the lamp tap, since plate current isn't being drawn through it. THis would make it last LONGER. The pilot lamp will be dimmer, but will still glow alright. ....And I'm not questioning whether or not the tube will last a shorter time. I'm firmly stating that having the tube wired per the schematic will NOT shorten its life. The 18 ohm resistor provides adequate 'cushion,' too, that might otherwise be provided by the lamp tap. Nothing is wrong with how it is wired in the schematic, other than that the pilot lamp will be dimmer.
There is something else dimly recalled about having a cushion in case the radio is turned off and back on suddenly.
:
:As for the 50L6 cathode resistor, 150 ohms is standard for this tube in this circuit with these voltages. I don't recall the last time I saw another value. Every 50L6, 50C5, 35L6, 25L6, and what-not on a 120 volt AC/DC circuit that I've ever seen has had a 150 ohm resistor for bias, unless bias was obtained by other means.
:
:The oscillator trick will provide extra bias. The thing I wonder about, though, is that the bias would change over the dial (since oscillator voltage changes over the dial). I have seen this trick used before in battery receivers, where it was undesirable to provide bias via dropping resistors (wasted power).
:
:T.
Yeah, that's a good point about the DC changing as the radio is tuned across the dial. Maybe the designer wanted to show the world he knew of a different way to build a radio, thereby impressing us with his wisdom. In my case, it didn't work too well.
Lewis
Is the lamp really wired this way? The lamp will be very dim if it matches the schematic. The schematic may be wrong? You already found biasing for the output tube doesn't match.
Norm
::As far as the rectifier is concerned, I don't know why it would last any shorter than otherwise.
:
:As I recall, it has something to do with unequal warming of the filaments when the radio is first turned on, and the hot filament current being lower than the cold filament current, and the B+ current not flowing until the smaller tubes start heating and drawing current, then part of the rectifier tube filament is lit with DC.
:
:
: Having the rectifier wired as per the schematic has less current flowing through the lamp tap, since plate current isn't being drawn through it. THis would make it last LONGER. The pilot lamp will be dimmer, but will still glow alright. ....And I'm not questioning whether or not the tube will last a shorter time. I'm firmly stating that having the tube wired per the schematic will NOT shorten its life. The 18 ohm resistor provides adequate 'cushion,' too, that might otherwise be provided by the lamp tap. Nothing is wrong with how it is wired in the schematic, other than that the pilot lamp will be dimmer.
:
:There is something else dimly recalled about having a cushion in case the radio is turned off and back on suddenly.
:
::
::As for the 50L6 cathode resistor, 150 ohms is standard for this tube in this circuit with these voltages. I don't recall the last time I saw another value. Every 50L6, 50C5, 35L6, 25L6, and what-not on a 120 volt AC/DC circuit that I've ever seen has had a 150 ohm resistor for bias, unless bias was obtained by other means.
::
::The oscillator trick will provide extra bias. The thing I wonder about, though, is that the bias would change over the dial (since oscillator voltage changes over the dial). I have seen this trick used before in battery receivers, where it was undesirable to provide bias via dropping resistors (wasted power).
::
::T.
:
:Yeah, that's a good point about the DC changing as the radio is tuned across the dial. Maybe the designer wanted to show the world he knew of a different way to build a radio, thereby impressing us with his wisdom. In my case, it didn't work too well.
:
:Lewis
Lewis L.
Lewis L.
Peter
:
: Is the lamp really wired this way? The lamp will be very dim if it matches the schematic. The schematic may be wrong? You already found biasing for the output tube doesn't match.
:
:Norm
:
:::As far as the rectifier is concerned, I don't know why it would last any shorter than otherwise.
::
::As I recall, it has something to do with unequal warming of the filaments when the radio is first turned on, and the hot filament current being lower than the cold filament current, and the B+ current not flowing until the smaller tubes start heating and drawing current, then part of the rectifier tube filament is lit with DC.
::
::
:: Having the rectifier wired as per the schematic has less current flowing through the lamp tap, since plate current isn't being drawn through it. THis would make it last LONGER. The pilot lamp will be dimmer, but will still glow alright. ....And I'm not questioning whether or not the tube will last a shorter time. I'm firmly stating that having the tube wired per the schematic will NOT shorten its life. The 18 ohm resistor provides adequate 'cushion,' too, that might otherwise be provided by the lamp tap. Nothing is wrong with how it is wired in the schematic, other than that the pilot lamp will be dimmer.
::
::There is something else dimly recalled about having a cushion in case the radio is turned off and back on suddenly.
::
:::
:::As for the 50L6 cathode resistor, 150 ohms is standard for this tube in this circuit with these voltages. I don't recall the last time I saw another value. Every 50L6, 50C5, 35L6, 25L6, and what-not on a 120 volt AC/DC circuit that I've ever seen has had a 150 ohm resistor for bias, unless bias was obtained by other means.
:::
:::The oscillator trick will provide extra bias. The thing I wonder about, though, is that the bias would change over the dial (since oscillator voltage changes over the dial). I have seen this trick used before in battery receivers, where it was undesirable to provide bias via dropping resistors (wasted power).
:::
:::T.
::
::Yeah, that's a good point about the DC changing as the radio is tuned across the dial. Maybe the designer wanted to show the world he knew of a different way to build a radio, thereby impressing us with his wisdom. In my case, it didn't work too well.
::
::Lewis