RedPlated
Well-known member
This amp started as a 90’s JCM800 non master volume model. The owner is a RT member and wanted the ability to tame the massive volume of a 1959 and add some gain and flexibility without the need for pedals.
These amps are PCB mounted pots and different PCB than earlier amps. I had to convert some of the pots to flying leads to make it work. I then converted the circuit to a cascaded 800 MV setup. On top of this, I added a gain structure switch and a signal enhance switch that adds extra gain in either the high mid region or deeper frequencies. These were placed in the two extra input holes.
NFB and depth were added on the rear. As well as a SAT switch and a SAT level control, to blend the diodes in and out of the circuit. As most of you know, this is sort of my signature feature with amps that I build/ mod.
This amp will become a stock 800 essentially with all switches off and depth and SAT turned off. This clip is at pretty much max gain with SAT on, but dialed back, and both options switches on. I did not convert this amp to Jose MV like most that I do.
I also adjusted all the B+ preamp voltages in the amp. They are way off spec in stock form. I had to get creative and add some dropping resistors and increase values to get all the nodes correct. It also needed a power tube socket replaced and had a bad screen resistor, so it was running on 3 tubes when received.
These amps are PCB mounted pots and different PCB than earlier amps. I had to convert some of the pots to flying leads to make it work. I then converted the circuit to a cascaded 800 MV setup. On top of this, I added a gain structure switch and a signal enhance switch that adds extra gain in either the high mid region or deeper frequencies. These were placed in the two extra input holes.
NFB and depth were added on the rear. As well as a SAT switch and a SAT level control, to blend the diodes in and out of the circuit. As most of you know, this is sort of my signature feature with amps that I build/ mod.
This amp will become a stock 800 essentially with all switches off and depth and SAT turned off. This clip is at pretty much max gain with SAT on, but dialed back, and both options switches on. I did not convert this amp to Jose MV like most that I do.
I also adjusted all the B+ preamp voltages in the amp. They are way off spec in stock form. I had to get creative and add some dropping resistors and increase values to get all the nodes correct. It also needed a power tube socket replaced and had a bad screen resistor, so it was running on 3 tubes when received.
Last edited:
