Blair wrote:When using a tube rectifier into a cap input supply, say using 6BW4, do you need to stick with the 40uf maximum cap size in position 1 if you use a choke input supply? I have a 700VCT transformer and a 20H choke I'd like to use for a preamp.
Nope you can put any cap you want after the choke. Remember that the cap might still see 350 X 1.4 or 490VDC, so you'll need a 500V rated cap. I would rather want a 500CT or so transformer for a preamp, so I could use cheaper 400 - 450 volt capacitors, and use the sweet 20H choke after the cap. How much current is that transformer rated for?
Blair wrote:I was also curious the other day about paralleling the plates on the 6BW4. Is that OK? I was thinking about using a pair in a doubler configuration. Why? I have a half dozen or so, and the voltage drop across the plates is usually too much for the transformers I get or have on hand.
Thanks!
Blair
Using tubes in a doubler is difficult, because of the increased current going through the rectifiers. You can parallel the plates, but you would need 2 6BW4s and probably 2 silicon rectifiers. Paralleling the plates gives you half of the tubes resistance, so using 2 6BW4s in a full wave rectifier will yield a maximum of 200ma. A Chinese or Russian 5AR4 will yield 260ma with less drop, and they are cheap.
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