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40-155 transformer output - Printable Version

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40-155 transformer output - bridkarl - 10-04-2025

My 84 rectifier tube showed it was gassy with a violet flare so I replaced it.

I checked today and at 120vac I’m getting 535vac to the rectifier socket. Also about 7vac to the filaments. 
For the 32-8065 transformer does this sound about right? I’ve looked through the catalog and didn’t find the specs for this.

RE: 40-155 transformer output - MrFixr55 - 10-05-2025

Hi Bridkarl,

Is that no load values or with all tubes in? Nominal filament voltage for all tubes is 6.3V, but these are car radio tubes and running at 7V in a car is not unheard of. This set should have about 185VDC into the output transformer, and 270V at the junction of the rectifier cathode and Cap # 61.

The power spec is 115VAC. 120V is about 4.3% higher. This would make the filament value approximately 6.6 V.

RE: 40-155 transformer output - bridkarl - 10-05-2025

That was no load. Just the multimeter leads in the tube socket.
I’ll check the voltages again once I get the replacement rectifier tube in a few days.
Otherwise there were no observed issues - smoke, heating, etc. aside from the obvious gassy 84 tube.

RE: 40-155 transformer output - morzh - 10-05-2025

For a good transformer the no-load and load values should not be too different, but then your difference is not that much. After akk, the output winding has some finite resistance. And, possibly, your radio is supposed to work at 110-115V, which would explain most of the difference.

RE: 40-155 transformer output - bridkarl - 10-09-2025

Replaced the tubes. Powers up with about 40 watts usage. Zero audio. Going to start working backwards from the speaker. I’m starting with the assumption the audio transformer has an issue so I’ll use my ohmmeter and check the windings.
 Update 10/11

Spent about five hours today on this. Mostly
replacing bad rubber wiring. The wiring on the speaker was bad so replaced that. Also the audio transformer showed short so replaced that. General check of work to date, reflowing soldering, checking wires in right places.
Current status is it powers up. No audio except a very low hum. Volume and tone controls modify this hum so these circuits apparently work. 
Caps all replaced. Waiting on resistors to start checking and replacement.
Have an unmodified unit side by side on bench so that’s helpful. 
Bad volume control?? It’s been replaced at some point with this small random switched pot. Soneone just threw in a part.  Replacing with 2 megaohm linear Allen-Bradley pot so this is correct per schematic. 
Mostly cleanup work today. Making sure power supply caps are properly mounted and not just hanging in space.