So I have a 1983 Super Champ here that I recapped and before sending it back to the owner I wanted to pick your brains about what could cause a weird warbling kind of sound to come from the amp after powering it on. I have a video of the noise but don’t know how to post it here but I can email it to anyone interested.
Basically after turning the power on, after about 10 seconds it makes a loud warbling sound that increases in speed and intensity until it suddenly fades away and then the amp is ready to go. Needless to say the whole thing just gives the impression something is wrong with the amp and I don’t want to return it this way. I can’t find any components that are bad or out of spec so any pointers here would be greatly appreciated, thanks!
Diagnosing odd sounds at start-up
Moderators: pompeiisneaks, Colossal
Re: Diagnosing odd sounds at start-up
Maybe one of the sections of the new can cap is a bit weak, eg high esr or something?
I suggest to temporarily clip a known good 22uF 500V cap across the reservoir (OT / anode), then the screen grid node, checking for the start up oscillation each time.
I suggest to temporarily clip a known good 22uF 500V cap across the reservoir (OT / anode), then the screen grid node, checking for the start up oscillation each time.
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Re: Diagnosing odd sounds at start-up
I will try that and report back, thank you.
Re: Diagnosing odd sounds at start-up
the layout that i am viewing has a 70uf 100v cap at the end of the board i would jumper this as well and any other caps connected to the reverb circut for diagnostic purposes
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Stevem
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Re: Diagnosing odd sounds at start-up
Did the amp not do this before the cap job?"
If you remove that 12 pin compaction tube does the issue still take place?
If you remove that 12 pin compaction tube does the issue still take place?
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Not screaming like the passengers in his car!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Diagnosing odd sounds at start-up
It was doing this before the cap job but I tackled the basic re-cap first before venturing on to this.
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Stevem
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Re: Diagnosing odd sounds at start-up
Since the amp was doing this before the cap job it might be one of the output tubes also .
Remove them one at a time to confirm this.
Remove them one at a time to confirm this.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Diagnosing odd sounds at start-up
Yes the output tube idea was a great idea; it didn’t occur to me but it makes sense because I was already thinking of things that warm up and/or charge after initial start-up and I was thinking some capacitor the whole time.
There was an annoying ringing noise in the background too that got louder and louder the last couple days so I touched the output tubes with gloves and the ringing stopped when I touched one of them so I think it’s a very unhealthy tube. I replaced it with a similar tube and the warbling and ringing microphonics have stopped.
There was an annoying ringing noise in the background too that got louder and louder the last couple days so I touched the output tubes with gloves and the ringing stopped when I touched one of them so I think it’s a very unhealthy tube. I replaced it with a similar tube and the warbling and ringing microphonics have stopped.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Diagnosing odd sounds at start-up
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!