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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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need help with Tube amp mod
I have a "legend super lead 100" guitar amp from
the 1980s. Very cool looking amp, solid finger-jointed oak cabinet. It has a 12ax7 preamp that sounds pretty good. But the "color gain" doesn't work right. At 0 you don't get any sound. At higher settings, the amp works but no "color" occurs (ie clipping @ CR1/CR2). I'm in a little over my head here. The color gain is not wired exactly according to the schematic (problem, or post-production tweak?). Schematic (149kb): http://www.telusplanet.net/public/beaumac/preamp.gif Actual factory wiring (24kb): http://www.telusplanet.net/public/beaumac/actual.gif The actual wiring prevents the "shorting" of R10 @CCW thereby preventing significant "color"(right?). R9 goes to ground @full CCW. This acts as a volume control on low settings, which it shouldn't do (signal at the grid of V1(2) to ground). Is this just bad design? Would this work instead? Do I need to worry about current flow at the grid V1(2)? http://www.telusplanet.net/public/beaumac/new.gif Any help appreciated. |
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