I need to reduce the output of a toroidal transformer by a few volts. Rather than strip some turns off will it work if I wrap the appropriate amount of turns needed around the outside of the transformer and put this in series with the primary? Does it matter where it is wrapped or can I just evenly spread it out? As long as I use large enough wire for the current draw I should be in good shape correct?
Evenly spread them out, but yes it will work. Functionally you will be reducing the volts/turn impressed on the primary winding. Transformers are amazing devices.
Get the polarity wrong and you increase volts/turn.
Get the polarity wrong and you increase volts/turn.
I suggest to add windings to the secondary and connect "out of phase" to reduce the voltage. that way you avoid touching the primary.
Bucking transformers work great to reduce the output by a "few" volts. Also, the required VA rating of the transformer can be minimal; perhaps 5 or 10 VA is more than adequate. What size transformer are you working with?
I'm not current considering a design. I was thinking of using it with an isolation transformer to get the B+ down to around 200V for a SE triode design I was considering using the UB!-1 transformer from One Electron as output. The other alternative would be to use a buck regulator to step down the output.
Oh, and the tube in question is the 6S41S, a triode normally used as a linear pass regulator, so should have pretty low plate resistance. I was thinking of biasing them up at 200V, 100mA, well within the 25W plate rating. They are supposed to have around a 170 ohm plate resistance, so a UBT-1 output transformer at 1.6k impedance should be an easy load.. I was thinking of biasing the tube with an active voltage source, to avoid excessive degeneration of gain at the cathode. I may need a moderately substantial heat sink, as I would be dumping 8-8.5W per channel in the voltage sources.
Last edited:
OK - I think I have the architecture sorted out. I'll use the unrectified output of the isolation toroid to power a depletion mode Mosfet front end. The extra voltage will grant the mosfet some authority to drive the triode. That rough rectified voltage will get stepped down by a buck regulator to ~200 VDC to power the output stage. I'll probably end up using feedback from the output to the mosfet front end.
I'll think about it. The buck converter would be a borderline discontinuous discrete design, so I would probably show that as " a box with stuff inside".