Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Voxbox on May 10, 2014, 05:37:39 pm
-
Hi,
At risk of sounding like a complete newbie, which in some ways I am...
What would be the expected ripple at the Power valves at 450V?
I know it should get cancelled out in the OT....but that's assuming that the OT is perfectly balanced.
cheers, VB
-
That depends on the size of your filter caps and how much current is pulled from the supply. And if you are measuring at the first filter cap or if you have 2 stages of filtering before feeding the output tube plates.
All that said, I wouldn't be alarmed by 5vac or a bit more at the plate node.
-
1% is too low (you paid too much for your filtering).
5% is rather high.
Some geetar amps do run 10% at FULL output, but less at idle.
-
Take a "40 Watt" amp. At full roar it runs 450V 225mA. Say it has a 40uFd main cap, and the push-pull OT is fed from there.
-
Good on PRR for supplying the tech data. 10% (45 volts) would kind of surprise me. 3-5% (15-30 volts) is to expected in toobland.
I was gonna say, 1% (4.5 volts) is a rule of thumb that in a world of +/-10% all-day-long tubes----without electronic regulation and silly amounts of filter caps, you probably cannot get under that "no matter what". That's of course at idle; pulling more current (louder power chord) or getting closer to the capacity of the power transformer would increase PS ripple. Presence of a choke (or not) would make some difference, too.
Know that plenty of hi-fi amps were built in the 50's and 60's with 4 ufd and 8 ufd filter caps...and this in an era when "hum and noise" were the holy grail specs.
It probably should be pointed out that there are different kinds of ripple...you are likely thinking about full or half wave ripple, 60 or 120 Hz. If the supply uses noisy silicon diodes (and regular old 1N4007's are somewhat noisy) those create switching transients which are absolutely visible on a scope and which your nominal 20-40 ufd filter caps are NOT very good at smoothing out.