Columbia 360 "Series B" Amp Repair

[Billrnst]

I have this formally wonderful Columbia 360 record player that was handed down through my family. After some lubrication and cleaning to the changer it worked and sounded great for 2 years or so. Slowly it developed a low hum...you guessed it now there is no sound.

Before I start rebuilding the amp is there anything I should check to verify there is no major damage that won't be easily repaired?

I attached a photo of the schematic since I see no specific model numbers. Amp is listed as Series B amp and cabinet 2201.

Thanks in advance for your time and assistance.
Bill

http://imgur.com/OL9Ij

[mstaton]

Sounds like the electrolytic filter caps took a dump. Sounds like it's in need of a re-cap.

[Billrnst]

That's what I thought as well but would bad caps alone cause no sound not even hum?

[bob91343]

Do the tubes light? Is there B+? Is the speaker properly connected?

[mstaton]

Maybe a tube bit the dust. You need to check tubes and voltages first.

[electroking]

As long as the output transformer (rightmost on the schematic) has good windings,
this amplifier is easy to rebuild. All other parts are esaily available.

This is a rather basic amp, with series-string tubes, but being a push-pull unit
(two output tubes), it may be worth keeping and rebuilding, as noted above.
Good luck!

[Billrnst]

Thanks for all the advice!

The windings seem okay as best as I can tell, VOM reads 196 ohms and the tubes do light.

I'll let you know how it turns out.

Bill

[radiotvnut]

Often, the filter caps cause hum and then the cap becomes very leaky or shorts. When this happens, the shorted/leaky caps will destroy the rectifier tube and/or the surge resistor in the power supply. When this happens, the amp will be dead because there is no B+ voltage being developed. Since the output transformer test good, I'd replace the electrolytic and paper caps and then I'd check voltages.

[Billrnst]

Thanks for all the advise. So far I've replaced the electrolytic and paper caps (no change) then changed 35Z5GT. Now I have low hum but no audio from the cartridge. Cartridge is working when connected to a known good amp (used aux in on receiver). Next I'll change the 12AX7, will let you know what happens when the new tube arrives.