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Hi Tinman,
Modern replacements will meet the original specs I quoted for currents, unless a PT supplier is building a tweaked version with greater current capacity (not a bad idea). Many factory 125P1B will run voltage equal to, or more than modern replacements. A PT will only be "too much" for a champ if the B+ results in dangerously high B+ for the tube at a reasonable current draw. Many custom amp builders use PTs that are capable of much greater current capacity than original Fender PTs, it's not a problem.
The confusion stems primarily from the fact that the voltages listed on tolex champ schems are low, compared to real life scenario.
FWIW my SF champ with fixed bias & original PT runs 450vdc at 30mA in fixed bias.
Richard M wrote: "From an amateur like me, if the PT is "overbuilt" surely it would be only in the current (amps) it can supply not the voltage?" One affects the other, draw less curent & voltage goes up, draw more current & voltage goes down. If the PT is "overbuilt" these deviations will be less at a reasonable current draw. Again, going back to my SF Champ, If I install a 6L6 and bias up to 50mA I get 390vdc on the plate due to the greater loads on B+ & heater windings...if the PT was substantially overbuilt then the voltage drop with the higher loads would be less.
Modern replacements will meet the original specs I quoted for currents, unless a PT supplier is building a tweaked version with greater current capacity (not a bad idea). Many factory 125P1B will run voltage equal to, or more than modern replacements. A PT will only be "too much" for a champ if the B+ results in dangerously high B+ for the tube at a reasonable current draw. Many custom amp builders use PTs that are capable of much greater current capacity than original Fender PTs, it's not a problem.
The confusion stems primarily from the fact that the voltages listed on tolex champ schems are low, compared to real life scenario.
FWIW my SF champ with fixed bias & original PT runs 450vdc at 30mA in fixed bias.
Richard M wrote: "From an amateur like me, if the PT is "overbuilt" surely it would be only in the current (amps) it can supply not the voltage?" One affects the other, draw less curent & voltage goes up, draw more current & voltage goes down. If the PT is "overbuilt" these deviations will be less at a reasonable current draw. Again, going back to my SF Champ, If I install a 6L6 and bias up to 50mA I get 390vdc on the plate due to the greater loads on B+ & heater windings...if the PT was substantially overbuilt then the voltage drop with the higher loads would be less.
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