Hello I hope this forum works again.
I recently acquired a 76 JMP 2203 for a steal. It was made for the Canadian market but apparently before they added all those fuses and omitted the 16 ohm tap, so it's like a "normal" Marshall JMP 2203.
Anyway, it had been sitting forever and it's pretty dusty and crusty. I recapped the entire thing, also replaced the screen resistors and dropping resistors. Repaired some hack wiring mods. I slowly powered it up through a variac and I'm getting what seems to be very high B+ at full wall voltage. I'm seeing 530 VDC at the output tube plates and screens. I know some vintage Plexis had over 500 volts on the plates. I'm not aware of mid-70s master volume units having that much plate voltage though. I'm wondering if maybe this amp is one of those oddities made with leftover parts? It does have a laydown power transformer which is sort of odd for the time period of this amp. And it appears to be the original transformer. It still has the dye on the solder joints etc. Heater voltages are pretty normal though - 6.6 VAC. I'm wondering if this is just a crazy hot power transformer on the secondaries? The PT does have a very faint buzz to it at full wall voltage.
Anyway...I'm running the original 12AX7s in it and have a very gently used set of JJ KT77s in it for now. I just want to see it make voltages where they're supposed to be. But damn these voltages are high! What do yall think?
I recently acquired a 76 JMP 2203 for a steal. It was made for the Canadian market but apparently before they added all those fuses and omitted the 16 ohm tap, so it's like a "normal" Marshall JMP 2203.
Anyway, it had been sitting forever and it's pretty dusty and crusty. I recapped the entire thing, also replaced the screen resistors and dropping resistors. Repaired some hack wiring mods. I slowly powered it up through a variac and I'm getting what seems to be very high B+ at full wall voltage. I'm seeing 530 VDC at the output tube plates and screens. I know some vintage Plexis had over 500 volts on the plates. I'm not aware of mid-70s master volume units having that much plate voltage though. I'm wondering if maybe this amp is one of those oddities made with leftover parts? It does have a laydown power transformer which is sort of odd for the time period of this amp. And it appears to be the original transformer. It still has the dye on the solder joints etc. Heater voltages are pretty normal though - 6.6 VAC. I'm wondering if this is just a crazy hot power transformer on the secondaries? The PT does have a very faint buzz to it at full wall voltage.
Anyway...I'm running the original 12AX7s in it and have a very gently used set of JJ KT77s in it for now. I just want to see it make voltages where they're supposed to be. But damn these voltages are high! What do yall think?
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