38-7. No sound - Printable Version

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+--- Thread: 38-7. No sound (/showthread.php?tid=25220)

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38-7. No sound - sam - 09-04-2024

Hey guys 
Bought this radio in 2018 and put away bought it off eBay but I don’t recall seller saying it was restored  I pulled chassis out and caps have been changed and looks to be correct  problem is no Sound at all   Not even static  even when I touch 6j5 I pulled out 5y4 tube and  transformer didn’t even get warm  all tubes light and good dial light works and cone lock disconnected
What else could I check

Thanks sam

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RE: 38-7. No sound - radiorich - 09-04-2024

Hello Sam ,
First All here is the Schematic to help you with this set
https://philcoradio.com/library/download/service%20info/wiring%20diagrams/vol2/split/Part37-Philco%20Wiring%20Diagrams%20Vol.%202.pdf
I had a Similar issue with a set that I have on my bench and found out the Audio output transformer had a open winding !
Hopefully you have a Multimeter because that what I would do look over the set and start from the speaker .

Sincerely Richard

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RE: 38-7. No sound - MrFixr55 - 09-05-2024

Hi Sam,

+1 on Richard's comments.

If you have a DVM or VOM, arrange the radio with chassis upside down. Start with the output transformer and field coil. Ohm them to ensure that they are not open. The transformer secondary likely will not open but the voice coil or the flexible voice coil pigtails may open. Unsolder the leads to the voice coil terminals and ohm the voice coil and secondary.

Next, locate the wirewound resistor, #43 on the schematic and ohm across the entire resistor. It should be about 245 Ohm. If this resistor is open, it will cause the no sound, no current issue as it is between the B+ return and chassis ground (and the 6F6 output tube cathode). This resistor generates the "C-" grid bias for the audio tubes by "voltage dividing" the return from the B+ supply.

When you touched the 6J5 grid cap, was the wire attached or detached? If this set has "cone-centric" tuning, there is an audio mute switch, #29 on the schematic.

If all is good, set meter to 700V and CAREFULLY! Measure voltage across the filter caps. There should be about 350V across the input cap (#45, at 5Y4 heater), and about 250V across the cap on the other side of the field coil (#11A). Higher voltages on both sides indicates no current draw. Of course, the biggest draw is from the output tube. Since this is a class A biased output, there should be a lot of current draw even at no volume. No voltage across the input filter cap indicates an extremely bad 5Y4 (open heater) or open secondary (This would be rare as the secondary would have to be open on both sides of the center tap.

Next, check voltage between Pin 3 (plate) of the 6F6 output tube and the B supply center tap of the power transformer (ungrounded side of resistor #43). It should be about 240V. Next, check between Pin 4 (screen grid) of the 6F6 and the power transformer. It should be 250V. If no voltage at pin 3 but voltage at pin 4, then the wiring to the output transformer is open. Please note that if this is the case, the 6F6 is likely also bad, as an open plate circuit will cause such a high current in the screen grid circuit that the screen grid will glow brighter than the heater and burn out, possibly shorting the tube.

Hope this all helps.

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RE: 38-7. No sound - sam - 09-05-2024

hey guys 
rechecked found cap 34 connected to tap on candacome resister
reconnected to tap for 6j5 tube and it came alive very loud too
 if i now can get kirk to help with cabinet   
thanks guys


sam

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RE: 38-7. No sound - MrFixr55 - 09-05-2024

Yeah, that would do it. Cap has to go between plate of 1st AF tube and grid of output tube.

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RE: 38-7. No sound - morzh - 09-06-2024

Sam

Good luck with Kirk

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