model 41-280 no stations or sound - Printable Version
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model 41-280 no stations or sound - williec - 07-31-2011
I'm in the process of restoring a console model 41-280. I have a replaced the caps, the power cord, and verified the tubes and speaker are ok. I felt my next step should be to check tube voltage and this is the results: 41 output tubes read 160 and schematic says 175. Didn't check the 7c6 audio as the schematic dosen't give any value on voltage. Both 7b7 tubes read 158 versus 180 on the schematic. Finally the xxl tubes read 66 and 31 versus 95 and 40 on the schematic. My questions are are these readings acceptable and am I going about this in the right manner. This is my first attempt in restoring a vintage radio as you can probably tell. Any comments will be appreciated. Bill
Re: model 41-280 no stations or sound - codefox1 - 07-31-2011
Follow the B+ line and voltage divider resistors. One or more have most gone way up in value. When in doubt, replace. Cheap enough. Your voltage readings should be at or slightly above nominal values.
Schematic here
http://www.nostalgiaair.org/PagesByModel/415/M0013415.pdf
Re: model 41-280 no stations or sound - williec - 07-31-2011
Thanks for the reply but I guess I don't know what the B+ means.
Re: model 41-280 no stations or sound - codefox1 - 07-31-2011
No problem, start at the cathode of the 84 rectifier (pin4) with respect to the chassis. This is the B+ supply. Trace the path after the field coil and measure voltages as indicated on the schematic as the resistors further divide the supply. Hopefully you can then isolate the problem to a certain section.
Re: model 41-280 no stations or sound - williec - 07-31-2011
Thanks, I'll do that.
Re: model 41-280 no stations or sound - williec - 07-31-2011
Would anyone out there know what the plate voltage should be on the 84 rectifier and 7c6 audio tube for a 41-280. I don't see anything on the schematic for these 2 tubes. Also is there a + or - factor on plate voltage? Thanks, Bill
Re: model 41-280 no stations or sound - Radioroslyn - 07-31-2011
I've got a better question. What is the resistance of the plate resistor on the 7C6. Should be 220K is it? I'll take a guess and say about 75v.
The plate voltage on the 84 isn't that important as the set is making HV and is close to spec.
B+ is another way of saying high voltage. Goes back to the old days (1920's) when sets used batteries. A battery supplied the filament voltage, B battery supplied the high voltage and the C battery supplied the negative bias voltage for the audio stages. So B+ is a reference to the + side of the high voltage.
Terry
Re: model 41-280 no stations or sound - williec - 07-31-2011
Hi Terry, The reading I got on the 7c6 is 96 but I get a 87 reading on this same tube in another set I have and it works perfectly. Now can you tell me what's wrong and what my next step should be? Thanks, Bill
Re: model 41-280 no stations or sound - Radioroslyn - 07-31-2011
Ok Voltage seems good. When you say no sound do you mean there is absolutely no sound if not what do you hear?
Terry
Re: model 41-280 no stations or sound - williec - 07-31-2011
Just a faint humm and no speaker cracking when you turn the band selector.
Re: model 41-280 no stations or sound - Radioroslyn - 07-31-2011
Measure the voltages on each 41 tube. Pins 2,3,and 4 to chassis report back
Terry
Re: model 41-280 no stations or sound - williec - 07-31-2011
The 41 nearest the 84 tube readings are 166,158 and 5.5( speaker cracks when touching this post) The very back 41 reads 165,168 and 5.2
Re: model 41-280 no stations or sound - Radioroslyn - 07-31-2011
Ok that all good. On the 7C6 if you touch pin 3 with your finger it should buzz good and loud. does it?
Terry
Re: model 41-280 no stations or sound - williec - 07-31-2011
Terry, I get nothing at all.
Re: model 41-280 no stations or sound - Radioroslyn - 07-31-2011
Hmmmmm
Well there one problem. Is the 7C6 lit? Can you see the filament glowing? Do you have an audio signal source like a fm tuner, tape deck or something?
Should be a cap connected to pin3 (the plate of 7C6) over to the control grid of one of the 41's(pin4) Is it there?
Terry