Tube Amps / Music Electronics
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|previous: Mike Well, after having the amp for a we... -- 10/27/1999 1:19 AM|
|10/27/1999 1:41 AM|
|Farrow||Re: Sears Silvertone Twin Twelve|
I've got a head but no cab, and I'm sure there's others -- Maybe you'd be willing to split up the pair?
Here's what you can do that makes them worth keeping, FWIW.
First, get the schematic. It's in the Weber book, or I can email you a copy. Start with the power supply:
PSU uses a low-voltage (TV?) power transformer, maybe 100VAC across the secondary. It seends B+ thru a voltage doubler chain to get the HV on the tube plates. Ditch the PT and put in a Hammond or other similar iron. Cut out the voltage doubler and replace with a few 1n4007s in a full-wave rectifier. New filter caps, of course.
Preamp, mostly fine. Cut out the reverb tank, and mount a 47ohm resistor across the terminal strips where the reverb tank was originally connected. This turns the reverb control into a footswitchable gain boost, very tasty. The 6CG7s sound awful nice used like this. PERHAPS you should rewire the 6CG7 socket for the phase inverter to take a 12AX7. I think you only have to cut the wire off pin 5 and move it to pin 9. This gives you a bit more preamp gain.
Power amp - I like to rework the power amp to take 6V6s. I cut out the bias supply and put in cathode resistors and a cathode bypass cap. Value depends on plate voltage. I like to run them at ~350V for a nice blues tone. Other than that, it's mostly okay. You COULD replace the OT, but with 6V6s it's more than adequate. OTOH I also like EL34s in this amp, in which case you'd want a beefier OT.
Keep in mind that this amp is NOT NOT NOT a real good mod platform. The chassis is small and all the controls are mounted to the folded-up "front panel." Also it's flimsy and old. You might be better off selling this thing on ebay since the cab is in good shape (#1 casualty of the vintage amp world is missing Twin Twelve cabinets and buying a Traynor Alternatively, I have a junker sitting in my shop now - PT's fine, no OT, no reverb tank, no tubes, that I'd sell for $50. This would let you play around with the amp and you'd still have yours in good shape if you get strapped 4 cash or whatever.
|pumpstein Why change the PS (voltage doubler) setup? -- 10/27/1999 5:09 PM|