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FDP Forum / Amp Mods, Repairs, and Projects / Low Power Tweed Twin build - very low volume, treble control unresponsive

vanceen25
Contributing Member
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United States

Vance Erickson
Jul 14th, 2019 02:11 PM   Edit   Profile  

I just put together a low power Tweed Twin using material from Ceriatone. The problem I'm having is that the output is very low at any volume setting. I've also noticed that the Treble control seems to do nothing at all (the Bass and Presence seem to be working). Actually, it sounds very nice, it's just very quiet, much quieter than a 1W amp.

Voltages on all the pins are OK. I've changed out all the tubes except the rectifiers (if they weren't OK, I wouldn't be gettting the correct voltages, right?) I've changed out speaker cables, speakers, guitar cables, and guitars, always with the same result. I've looked closely at the wiring on the pots and poked around, with no result. I've chopsticked everything, with no result.

Has anyone come across anything like this? I'm thinking it must have something to do with the tone stack wiring, and that most of the signal is getting shunted to ground somewhere. I've got an oscilloscope I can take to it, but I wanted to hear what the amp gurus on here have to say before I do that.

Thanks in advance!

Peegoo
Contributing Member
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If irritation occurs

discontinue use.
Jul 14th, 2019 03:58 PM   Edit   Profile  

I'm no amp guru, but I've run into this in a biuld, and tracked it down to a bad 68K resistor between the input jack and a 12AX7 V1.

Did you test your components before you built?

vanceen25
Contributing Member
***

United States

Vance Erickson
Jul 14th, 2019 04:45 PM   Edit   Profile  

Yes, I measured the resistors and caps (where possible) before I put them in.

This happens with all four inputs. As I understand it, all four 68k grid stoppers would have to be bad to cause the problem.

But thanks for your input!

Peegoo
Contributing Member
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**********
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****

If irritation occurs

discontinue use.
Jul 14th, 2019 08:18 PM   Edit   Profile  

I wasn't suggesting is was a grid stopper; that was just an example.

It could be a bad output transformer.

It may be something as simple as an open ground in the signal path.

(This message was last edited by Peegoo at 10:19 PM, Jul 14th, 2019)

vanceen25
Contributing Member
***

United States

Vance Erickson
Jul 15th, 2019 01:38 PM   Edit   Profile  

I seem to have pretty much cracked it. I loosened the tone and volume knobs and it worked fine. Something was jammed in there too tight, probably grounding something. I'm rewiring the tone & volume knobs to make sure I don't have an intermittent problem. Thanks for your suggestions.

FDP Forum / Amp Mods, Repairs, and Projects / Low Power Tweed Twin build - very low volume, treble control unresponsive




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