Stephand wrote:
Thanks for your quick answer
The 0.1uF output coupling make sense since it look to be the Norm for this type of mod.
Did you try the 2.7K/0.68 on the cathode on V1a/b and V2a? I saw other Shem with this value
Did you also put the Diode?
Thanks
Stephane
Stephane,
I used 0.1uF for the output coupling caps. Nice fat, tight low end. No, I did not use 2.7k/0.68uF on any stage --- 820R/0.68uF straight across. I made the first stage bypassable via a relay so it would be either 820->820 or 820->820>820. With just two stages, you get the full plexi vibe. Switch in the added gain stage in front (remember I used 330k instead of 430k on V1a) and it gets more modern sounding. There was the usual slight jump in gain hiss but overall the amp was remarkably quiet. I used the Larry Grounding scheme.
Yes, I did add the diode clipping stages just after the cathode follower. The 12V zeners give a killer sound, very modern but they do suck out some overall volume. I think I used either 16 or 20V zeners for the other side. The diode clipping switch was a 3-way on-off-on and the middle position was "off", no diode clipping. The 16/20V zeners give some nice added crunch for a more 80's style sound. I really liked the amp with both bright switches engaged (470pF) and the 12V zeners in. Cranked up with a 7-string and the tone was pretty amazing. I actually used a 5k8 primary OT and set it up to be switchable between EL34s and 6L6s (switchable bias circuit...client request) so it was not going to be "pure" Plexi sounding with that primary. Sounded killer though, more modern in a way, very tight and warm. Not at all trebly. I used polypropylene IC coupling caps throughout and Sozos in the tone stack. Very clear sounding with great note-to-note separation. Of note, if you turned down gain one and two and the preamp master, with the bright switches engaged, the amp gave an amazing chimey clean tone...really nice sounding. But the amp was for distortion
Hope this helps.