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Post by archiestone on May 19, 2020 11:49:59 GMT -5
A few months ago I bought a gently used Carl's Amplifiers Tweed Champ clone. A terrific sounding amp -- but... I am having an issue with a hissy distortion only evident at certain frequencies. No popping or volume issues, nothing but a lingering hiss when certain notes are played. (It tends to slowly decay then cut out abruptly at lower volume.)
I've tightened everything down, tried replacing the 6v6 and 12ax7 tubes - no change. (Haven't changed the GZ34 Rectifier tube because I don't have one.) Capacitors look fine - no leaking or swelling.
It's not the speaker (Weber Sig 8 Alnico.) Swapped that out too - no change. When I hook it up to an external cab it is considerably less evident but still there, so something to do with internal vibration is probable.
Any ideas? This is driving me nuts. I'd hate to pay an amp tech $100 to tell me it's a 25 cent part. A virtual Duff's to anyone who can help me debug this thing! Peegoo? ... Willie? ... Bueller?
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Post by Peegoo 🏁 on May 19, 2020 20:08:48 GMT -5
Hey Arch.
The grid leads on the preamp tube (pins 2 and 7) can sometimes be sensitive to lead dress (wire routing).
Get yourself a wooden chopstick and an assistant to hold the guitar and play the offending note(s). With the chassis open and one hand in your pocket, use the chopstick to gently nudge these grid wires a little bit out of their current positions to see if this clears up the oscillation you're getting.
Let us know if this has any effect on the problem.
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Post by archiestone on May 20, 2020 19:00:42 GMT -5
Peegoo - Thanks for the tip. I did what you said and noodged a few wires into different places, paying special attn to pins 2 and 7. No appreciable change. I did notice the socket on 7 is a little loose so I might try some gentle retensioning.
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Post by Peegoo 🏁 on May 22, 2020 17:18:44 GMT -5
It may be poor contact in the tube sockets; oxidation in them can make this noise occur.
It may be the rectifier tube. Sometimes the internals can be a little loose and vibrate. The rectifier does not handle signal, but if there are loose components, that noise can find its way into the signal.
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Post by archiestone on May 23, 2020 13:07:28 GMT -5
Not the rectifier tube. Found replacement, no change.
I think tube socket contact on the 12ax7 is a likely culprit. Planning to replace.
Thanks again.
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