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Funny power supply idea?

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6/22/1999 4:27 PM

Funny power supply idea?

While letting my mind drift while my computer was crunching some data, I thought of a wierd power supply circuit that I haven't seen before and wondered what y'all thought about it.

I have a tweed Princeton clone with one EL34 in the output. The amp puts out around 6W at clipping, mainly due to the low power supply voltage- 500VCT PT with a 5Y3 for about 300V out. The EL34 and the OT I am using should be good for around 10W, and I assume I need more HV to get the power up.

I thought about rewiring the PS from a grounded center tap full wave to a bridge, by lifting the center tap and adding two diodes to the 5Y3 and grounding their anodes. But the tone is great as it is- is there any way to switch between the two types of bridge rectifiers?

How about this- take a SPDT switch, ground the center lug or switch common, connect one side to the PT center tap and the other side to the anodes of the diode. You would then have basically a half voltage (roughly) switch to lower the B+, and change the output power and tone accordingly. Also, you could take a DPDT, use one side to switch the supply, and use the other to change bias voltages for the differing B+. After I think on it some more, I may try it on the amp.

Any comments?

6/22/1999 5:45 PM

Yeah, the CT/diode switch circuit works. It's used in some power supplies.

You will get just about twice the voltage out of the supply. The loading on the transformer will maybe more than double as you'll have a higher output voltage and likely higher output current through the tube, so watch for transformer overheating. The appx doubling in power will make it only slightly louder. The output transformer will also have about twice the power going through it, so make sure that it's intended for that much power AND that much DC in it's primary, or you'll be saturating it, with unfortunate results.

6/22/1999 6:15 PM
gfr	The Fender "The Twin" (red knob) uses a similar scheme for low power / high power switch (a DPDT for simultaneous half/full voltage selection and bias shift). It only doesn't use a tube rectifier.

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