Here's a tip if your amp is too mushy. Put an EQ in front of your amp and set sliders like in this image. This way it accentuates just the right frequencies. This effect cumulates downstream in the amp making it feel much "gainier" and crispier. And BTW, my six-band MXR handles 18Vdc for power...
I like the boost! I've modded it to be very close to 1987 but without cathode follower, and always play it little animal killing volumes master volume at 7 or 8.
If you are wondering is there diode clipping, there's not. There is less attenuation between first and second gain stages at certain frequencies when boost is on. Boost also switches on the cathode capacitor of the second gain stage. It's tube all way down.
How about these? Should be originals. I ordered a pair and got them within a week.
https://www.ebay.com/itm/Hitachi-MOSFET-2SK134-2SJ49-TO-3-1-Stk-1-Paar-o-2-St-ck-Transistor-Audio/254033483187?pageci=733dd323-634a-42b0-8b35-2f4d64af4a2d&redirect=mobile
At the ancient ax84.com site we experimented quite a bit to eliminate blocking distortion and duty cycle shifts caused by the grid current.
After so called "DC drive" was introduced by CarlB, the differences between "good" and "bad" tubes (in other circuits) were inaudible.
Schematic of the...
I have tubes to last my lifetime, but most valuable tool to manage my stash is a tubetester i build ten years back. I'll never part with it.
http://koti.japo.fi/~tivahal/Tubetester/Tubetester.html
Man, i did not know Bonk Industries were in amp business...
https://en.m.wikipedia.org/wiki/Bonk_Business
https://www.bonkbusinessinc.com/
Anyway, it would be fun to bring it back to life!
I just dug in little deeper into my ORI50, and i can now confirm that PI and power stage are close to conventional Marshall values. Couple things though; MV to PI coupling cap is 100n instead of 22n, PI grid resistors are 470k (1M), bias feed resistors are 150k (220k) and NFB is taken from OT 16...
Nothing weird in power amp, just what you would expect to see in Marshall. 150 kOhm grid reference resistors were nice find when i was trying 6550's, but i may actually change them to 220 kOhm as i prefer EL34's. Can't say for certain about presence-circuit, otherwise your drawings are spot on.
Sorry, no schematic for a whole amp, but power amp is a stock Marshall one, except for power scaling and 150 kOhm bias feed resistors. Power scaling works by dropping screen grid and PI voltages with MOSFETs, "low" and "mid" settings have set bias voltages which can't be adjusted, and that's why...