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Question about power tubes and Ot's

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  • #16
    Some considerations using ballpark numbers:

    With the Showman PT and SS rectifier the power tube plate supply voltage for the 4x6L6 at full output may be a little higher than in the original amp, let's assume +10%. Using the same load impedance this means +10% max. primary signal current. As a result max. output power will increase by about 20% and OT (copper) losses will increase by around 20% as well. Even if we add say +10% increase of OT core losses, the total increase of OT dissipation will be around 2W - not critical.
    What will suffer is the power tube screens, so expect reduced tube life.

    Things change if the speaker load is changed to 2 Ohm. This will increase available output to maybe 70W or 75W, but also double OT primary current. Meaning that OT copper losses will increase by around a factor of 4 resulting in a total OT power dissipation of maybe 20W. Thus the OT may overheat and eventually fail.
    Last edited by Helmholtz; 03-26-2019, 03:10 PM.
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