Hi
I have a Metro JTM45 rebuildt to JTM50 with EL34's, with Marstran 128 OT and 1986 bass spec's on the board. I would like to try some KT88's in this amp, obviously aiming for best possible headroom, clarity and punch. From what I can find searching the web, there's only small changes in the bias circuit; 220k split resistors down to 150 or 100k, and probably 56k for the bias resistor to get in range.
Would the PT be safe running KT88's or am I stretching the limit here? Would I need to bias cold, and not get the tubes up to good working conditions?
KT88 with 1202-55 PT
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allman
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Roe
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Re: KT88 with 1202-55 PT
should be fine, I guess. you're using the metro -55?
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Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39
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Super 100 amps: 1202-119 & 1202-84
JTM45 RS OT JTM50 JMP50 1959/2203/34/39
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allman
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Re: KT88 with 1202-55 PT
Roe wrote:should be fine, I guess. you're using the metro -55?
Yes, Metro 55 PT.
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Coot Boy
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Re: KT88 with 1202-55 PT
Filament requirements for EL34 is 1.5A, for KT88 it's 1.6A so you'll be right there, just be sure to bias as if it's a 25w tube ie EL34.