Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: terminalgs on September 07, 2012, 11:09:36 am
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I've built a few cathode bias amps using PT's with bias taps. I tape 'em off and ignore them. Idle Friday thoughts: Has anyone ever used one for an alternate purpose, like a DC filament voltage, maybe 12VDC for the preamp tubes? or a 24VDC supply for a transistor circuit?
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Not enough current available for much more than a low current bias supply. Certainly not enough for tube filaments.
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Not enough current available for much more than a low current bias supply. Certainly not enough for tube filaments.
doh! of course,, if the secondaries are at 120ma, the tape must be a fraction of that...
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And keep in mind the other issue is one side of the B+ winding is in common with the bias tap. Any current you suck from the bias tap steals current from the B+ when that side of the B+ winding is conducting through the rectifier.
You could do low-current voltage references, but there might be other, better ways of deriving those (like from the B+, which is already filtered and only needs to be knocked down to the desired voltage).
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> Any current you suck from the bias tap steals current from the B+ when that side of the B+ winding is conducting through the rectifier.
Yes; but only about 1/6th of the total turns.
If the HV is rated 120mA, I would not worry about taking 100mA of HV and 50mA from the 50V. 1/6th of the winding is overloaded, the rest is underloaded, and the way windings are done there won't be a hot-spot.
50mA is not enough for most heaters, as you say. Or relays.
The DCV will be close to 70V, far too high for conveniently powering op-amps and other chips.
You could use one of the larger Power Amp chips on 70V to drive a >150 ohm reverb tank.
It seems ideal for mike Phantom Power, but being common with the Power Output stage means output stage signal and transients would couple back to sensitive mike-input.
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I don't know if it worth the effort
from the bias winding, using a TL783, you can obtain a stabilized voltage to be used for opamps
K