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previous: Glenn Anyone cascade the channels of a 'P... -- 1117305497 View Thread

Re: Cascade 'Plexi' Channels???

6/2/2005 9:15 AM
anonymousRe: Cascade 'Plexi' Channels???
I've never gotten around to drawing this up, but if you are familiar with a typical Marshall MV preamp, this should make sense to you:  
Input jack to first stage - 34k resistance (the two stock 68k's in parallel), or a 33k will do.  
First stage cathode - 3.3k bypassed with 330mfd.  
Out from first stage, through .022 into a 1 meg pot. Bypass the pot with a .001 cap. Out from pot through 470k bypassed with a 570p cap, on to second stage.  
Second stage cathode - 2.7k bypassed by .68mfd (you'll notice this is the stock 1st stage values - you can save some time/trouble by just switching the wires on the first two stages).  
Out from 2nd stage, through .022, into 1 meg pot (use one of the now extraneous input jack holes). Bypass pot with a .005. Out from pot through a 470k bypassed with a 500p, on to third stage.  
Third stage cathode - 3.3k bypassed by a 330mfd.  
Change tone circuit cap from 500p to 250p.  
Everything else - leave as stock.  
Notes -  
-one could certainly argue that the 330mfd cathode caps could be smaller. This is probably true, but this value works well so I've never bothered to try.  
-the two "gain" or "preamp" knobs should be set in the 5-6 range to hit the sweet spot. You could replace one with fixed resistors, but I have found that tweaking the two pots in the 5-6 range allows for a good tonal variation (due to the bypass caps) that helps when switching between different sounding guitars, etc., so I put them both on the front panel.  
-Amps with EL34's or 6550's both sound very good. The 6550's sound "heavier".  
-I believe this is very close to the mods performed by Frank Levi in the late 80's. I first started tinkering with amps at that time, and dissected amps done by Levi, Soldano, Lee Jackson, etc.... so, nothing original here!  
Hope this is useful to you.

CB Sorry - that was me... -- 6/2/2005 11:56 AM