I replaced the filter caps and did some Plexi mods to it last Saturday. I came out really, really well.
Before
After
The work done:
I installed long overdue new filter caps.
I removed the 470k linear volume controls and put new 1 meg logarithmic volume pots in their place. I used a switching pull pot for the bright channel to control some preamp changes.
I swapped the 100k mixing resistors replaced with 220k. Antique Electronic Supply was out of 270k and naturally the local Radio Shack didn’t have them either so I used the closest value I had.
I replaced a .1 cap in the tone stack with a Mallory .022, replaced the slope resistor with a 33k and swapped out the 320pf cap with 500pf silver mica. That makes the tone controls a lot more useful.
I connected a 2.2k resistor and a 22uf cap to the switch on the pull pot which connects parallel to V1B's 1.5k cathode resistor when pulled. That provides a nice gain bump when engaged and is at stock value when off.
Lastly I replaced the 100K feedback resistor changed to 47k.
Everything is working perfectly. The volume controls are no longer on/off controls and the amp has definitely shifted to the Marshall camp in the tone department.
It was 25 deg in my shop when I did the work and I was frozen when i got it m=back in the house for it's test run. You can here it in my playing.
Here’s my frozen fingers test clip through a V30 loaded 212 cab.
Post mod clip, straight in with a Les Paul
http://www.youtube.com/watch?v=6N5a1KUPJrkWith a SD-1 pushing the front end
http://www.youtube.com/watch?v=H--f1b0blQs
