Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LooseChange on April 23, 2011, 07:25:34 am
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I've have a 65 Princceton Reverb on the bench. The reverb was not working for a long time but the amp was played. The problem was the input transformer leads were disconnected. All fixed.
The problem: With everything working, when the amp is played above volume setting 3, it sounds like a bad speaker. When the reverb send wire is disconnected the amp can be cranked and the problem goes away.
The reverb sounds fine when connected. The Speaker is good. The cables are good. The driver tube is good.
You think the reverb transformer is bad? You'd think it could go bad without a load on it just like any other output transformer?
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Just a guess, but the reverb tank could be bad. The wire for the receiving transducer (return end of the springs) is tiny and might have a weak connection. I worked on a vintage P.R. last year and had the reverb crap out on me completely just moving it on and off my workbench. I was lucky enough to find the broken solder joint for that tiny wire on the return end transducer and re-solder it.
That's not to say the reverb transformer couldn't go bad - but it's a whole lot easier to swap in another reverb tank first.
I'd also check the cathode bypass caps on the reverb driver and recovery tubes. Check the value of the 3.3meg mixing resistor too - the one I was working on had drifted up to almost 5meg and swapping in a new one made a world of difference.
The filter cap for the node supplying the reverb would be another possible culprit except the amp works fine without the reverb. Can you parallel another cap with that section of the cap can just in case? I know soldering on those vintage cap cans is NOT something I look forward too...
Hope that helps,
Chip