Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Apprentice on June 19, 2017, 02:30:36 pm
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I need a bit more help. I have built the BJ conversion from the Hoffman schematics and everything works ok. But I'm not really getting the typical BJ fender highs I was after when I first decided to do this build. I'm also not able to get a driven tone without blowing the house down.
I've checked my work over and over and can't see any issues. Any ideas for me to take a closer look at. I've checked the tone stack particularly carefully, maybe I'm just missing something obvious. I'm going to fit an L-pad so that I can wind the amp up to see how the tone sounds when at higher outputs.
Bias set to -12.7 volts. HT voltages are as per spec.
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I'd recommend shots of the insides, just so the crew can take a look and see what's going on, maybe they'll notice something amiss? It is possible you've miswired the tone controls so they're shunting some tone off and it's more of a fixed setup instead of variable. without seeing the actual amp wiring, it's a bit hard to guess. As I understand the Blues Jr conversion it removes the reverb but otherwise keeps the circuit the same no? (I've not done one, so I can't be super helpful other than to look at the schematic and layout and compare to the pictures you could post).
~Phil
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As a start - does your tone stack work at all? If not, check the ground on the Mid control. With no ground, you'll get mostly mid's and a lot more gain.
At what settings (Volume/Master) are you getting driven tone, but at blow-the-house-down volume?
Ed
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Thanks guys, I'm going to recheck once again the wiring on the tone stack. I'm convinced I'm all ok but just can't get the levels up so that the stack is working properly. I'm using the Vol pot on the Strat to cut the input so need to turn that up to properly test my theory. L pad with me on Friday. Will post results asap.
Thanks guys for responding, it was helpful to know that I'm not going to get anything too different from original bj. There are some value differences but not enough to alter things too much.
Thanks again