Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: VintageAmps on September 23, 2020, 11:26:23 am
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Hi guys , new to the forum and had a question about voltages. I am working on my first amp , a 1965 Fender deluxe and noticing the differences between measured voltages and schematic voltages. I realize this is due to wall voltages today vs then so the question is : do you fret any over the higher plate voltages or just concentrate on setting your plate current and dissipation?
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Assessment of the actual measured wall and heater Vac should be a crucial step in this process.
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Did you read note 1 on the schematic?
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Did you read note 1 on the schematic?
My view is that note regarding a 20% tolerance on voltage nominal values shouldn’t be read too literally, but rather understood via a sensible engineering context.
As for voltages at or closely tied to PT secondary windings, much tighter tolerances seem more appropriate. As tube heaters have a 10% voltage tolerance limit, and most of that would have to be ceded to the normal wall outlet variance. So at least two windings must have a far tighter tolerance than 20%, and it would be strange (though not impossible) to specify two PT winding to have say a 2% tolerance, yet to allow 20% on another. Especially as for some models, a HT voltage 20% over the nominal noted would cause the HT cap's voltage rating to be exceeded.
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I realize this is due to wall voltages today vs then so the question is : do you fret any over the higher plate voltages or just concentrate on setting your plate current and dissipation?
It is a case by case.
On some vintage amps with 6V6 / EL84, I reduce plate voltage ( B+) with zener diode stack.
Most of the time I work on amps with 6L6 or EL34 and I set only plate current and power dissipation.