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My understanding is that at high volume, plate voltage might sag below screen voltage, new production tubes will red plate under such conditions, these screen resistors will help avoiding this.
Thank you JCarno, I will try to record some clips during the weekend, but basically with boost off you get mild crunch and less highs. Photos attached.
Kris yes it's black grill.
What I meant is that as far as I know JMP 2104 circuit should be the same as the JCM 2104.
For reference in case anyone is interested, I compared a couple of things between the amp and the schematics:
1- Boost OFF adds a 15k resistor and a 0.47cap to V1A cathode's regular 2k7 resistor and 0.68 cap in series to ground. Boost ON shorts them to ground making this stage similar to JMP...
I recently acquired a rare 2144 combo dating back to 1980. It has the footswitchable boost and spring reverb, with two T1221 blackbacks (1979). I got it from its first owner and it's in a very good condition and little play time. Circuit, caps, transformers and preamp tubes still original and...
I recently acquired a rare 2144 combo dating back to 1980. It has the footswitchable boost and spring reverb, with two T1221 blackbacks (1979). I got it from its first owner and it's in a very good condition and little play time. Circuit, caps, transformers and preamp tubes still original and...