Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Madison on July 24, 2012, 09:21:33 pm
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Have a 5F1 Champ with PT failure.
All secondaries dead.
The amp is only about 9 months old.
Not sure how many hours were put on it.
Customer said he forgot and left it on all night.
He also removed the AC ground on the chord.
Would this cause a PT to go bad?
Wonder if I just got a lemon PT or the rectifier tube is shorting or ?
Rectifier tube was a NOS.
I hooked up another PT, amp seems to work fine.
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He also removed the AC ground on the chord.
Would this cause a PT to go bad?
no
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Customer said he forgot and left it on all night.
He also removed the AC ground on the chord.
On all night should do nothing but waste power. In fact, there are tube amplifiers in recording studios and broadcast stations that run 24/7 for years (maybe decades) and only stopped for tube changes.
The lack of the ground pin on the plug should also not kill an amp, but rather create a potentially unsafe condition should a major short to the chassis occur.
You hooked up a new PT, so I'm guessing that means you tried it with the previous PT. Since the new PT fixes the amp, can you try a safe method of testing the old PT to see how it might have failed?
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>>You hooked up a new PT, so I'm guessing that means you tried it with the previous PT.
Yes.
All secondaries were in the mV levels and the light bulb limiter was bright.
>>Since the new PT fixes the amp, can you try a safe method of testing the old PT to see how it might have failed?
My concern also.
I only have a 280-0-280 PT.
It works.
I left it on for a few hours and the PT was getting warm.
I am a little worried about the voltage coming off the rectifier.
It is at 340VDC.
This is high from what I understand.It is a NOS.
I think the specs for a 5Y3 is 1.1 increase with a 60V drop?
So there is a draw coming from the power tube or somewhere?
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I think 340vdc from a 280-0-280 PT is very typical for a real 5Y3.
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You could test the present arrangement if you have the time and inclination.
Figure out what your current draw should be at idle for the whole amp. Insert an ammeter between the rectifier cathode and B+ feed to first filter cap, and verify the amp's operation.
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Well, I have had this PT hooked up for a few hours now at idle.
It is a 100mA PT, a bit large for a Champ.
Have a 1A fuse inline that hasn't blown.
Good idea about the draw.Thanks!
It is drawing 39mA at idle.
I'd suppose that's about right.
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Some time ago in an italian forum we were discussing about a Champ clone
he had big problems about heat
the PT became very hot and the builder was forced to install a fan
I think that a bad engineered PT can also blow by himself if lost on power for a long time
a correct planned transformer don't
K