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Just past midnight last night, I fired up my first amp build, a BF Vibro Champ clone and it worked! But only my Volume and Treble knobs. The Bass knob wasn't changing anything, and no part of the tremolo circuit is working. Footswitch didn't change anything, speed and intensity knobs nada as well. Any clues on where to look for problems? Thanks.
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Check integrity of 15K resistor that is grounded from LH tab of bass pot?
Do a dc voltage check of the 12AX7s.
Oscillator caps OK, no broken leads?
Some pics would be good, as this is a new build (rather then a working amp) we really need to see what you have done, we can't assume the amp is built as per the schem. -
Checked the resistor on bass pot, it's fine. all connections to bass pot are fine.
How do I go about checking the voltages on the 12ax7's? I have a DVOM but what am I comparing the numbers to? Is there a chart somewhere of what everything is supposed to be?
Sorry I'm a total noob here. Here's a pic of my very messy wiring job.
DSC_0009.jpg picture by muse_ishin - Photobucket
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It's not really easy to see what is going on there, but your cathode bypass caps are not all oriented the same way, waisted end goes towards the tube pin.
Go to Schematic Heaven - FREE Amp Schematics Tube Amp Schematics Valve Amp Schematics Effect Schematics Effect Pedal Schematics Guitar Amp Schematics Bass Amp Schematics Fender Amp Schematics Marshall Amp Schematics Gibson Amp Schematics Vox Amp Schematics there is a vibro champ schem there...voltages don't need to match exactly, you're really just looking for them being in the right proportions.
In all honesty, I'd get a proper chassis & start again. Messy wiring is never good wiring...this alone can introduce problems. Google chassis shots of the vibrocham and copy the wiring layout as close as you can...you're still at the stage wherre it would be good to have someone close by to help/advise.Comment
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