78' FRIEDMAN KS JMP 2203

[JMP/HBE]

Re: 78' FRIEDMAN KS JMP 2203

V2a is a voltage amplifier in both plexis and 2203 circuits i believe. It ups the gain but doesn't clip, or if it does not very much. V2b is the cathode follower or the input to the tone stack is taken from the cathode of V2b.

There is something else going on with the 77 circuit revision on the master volume amps that should be pointed out, and which is germane to the later modded Marshall amps of the 80s by Jose and others that the BE type amps owes their legacy. The cathode resistor of V1B has been increased to 10k. To put this into perspective the shared cathode resistor on a 59 bassman is only 820 ohms. This makes the bias of V1B colder which causes it to clip the negative side of the signal earlier than the positive side as its being overdriven by V1A cascading into it. This causes an asymmetric clip. Asymmetric clipping is very organic and tubey sounding because it enhances even order harmonics.

This little trick was not new to Marshall. On the split cathode plexis the cathode resistor for the lead channel had been increased from 820 ohms to 1.8k to set up some asymmetric clipping and/or compression, especially if there was a boost pedal in front of the amp.

With an extra tube often added to modded Marshalls during the 80s, it was common practice to set up these extra gain stages to provide even more asymmetric clipping. For example, the Soldano SLO uses plexi value cathode resistors through the first two stages of the overdrive channel, but then V2B comes next. V2B is set up, not with a 10k cathode resistor like a 2203's V1B, but with a whopping 39k resistor. This "cold clipper" sets up a massive amount of asymmetric clipping. This topology was copied exactly by the Rectifier amps and the 5150s ...ect...

Agreed, you are Wise in the ways of Toan ...