JCM800 2203 Conversion from 6550 to EL34

  • Thread starter Thread starter Bxlxaxkxe
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Cap217 said:
On my 6550 2203 I ran them at 25 watts to be safer. I think it was a little cold but it still sounded ok. Running them a little hotter would be better though.

The 6550s were cleaner and more umph. With a 2203 JMP it made it more like acdc to me. Neither is better but thinking there will be a dramatic change isnt true. I do understand that its easier to find el34s though, that makes sense.

PS. My 2203 JMP came to me with el34s. The amp shipped with 6550s. Whoever the previous tech was didnt update anything. He installed el34s and biased it as hot as he could but when I checked it was running at 13. But the bias splitters were still stock 150k.
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Wow talk about leaving a shit ton of great tone at the table, not bothering to do it right..13ma?? Oof
 
Cap217 said:
Im curious about the PI cap values. I never looked into this in context.

EL34 - 220k splitter - .022 caps
6550 - 150k - still has the .022 caps right?
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Yes the 6550 Superlead and Master Volume 2203/2204 amps still ran the .022uf PI coupling caps with the 150K bias splitter resistors unless they were a Super Bass amp which then they would have had .1uf PI coupling caps.
 
The .1uf PI caps are mentioned in TomMitchell’s Tube Amp Book as a mod to make a Marshall more full sounding.
 
paulyc said:
The .1uf PI caps are mentioned in TomMitchell’s Tube Amp Book as a mod to make a Marshall more full sounding.
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It’s all personal preference. I hate the sound of larger PI caps. Makes the amp sound sucked into the cabinet as if the cabinet itself is projecting from a room. Just didn’t sound right to my ears and never has. As always YMMV.
 
My Martin modded se crunch jmp has .1 and it does sound full but looser.
 
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