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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.


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

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.

Cool. Thanks.

I think I will punch a new top plate on the preamp I was trying to salvage with the doubler unless someone knows of a 9 pin 200-250V regulator:(

Regarding current, I dunno. Enough for a preamp at least. It was an oddball out of my pile. Had a 5V and 3V filament windings. I had no use for it at all, but then I put them in series to run a pair of 8CG7 filaments, variac'd it and let it sit for a while with no voltage drop of significance or heat buildup.

I'm sure the HV winding is good for more than the 12-16mA I'm going to ask for out of it.



The transformer on the front is just to power the filaments of the 6BW4. It's a 2A potted Chicago. I had to fix the corners with a touch of bondo, but it turned out nice:)

Blair

When I needed to regulate the g2 on my 6L6-GC amplifier I used two OA2 (hope I remember that type correctly) in series an then used an high voltage mosfet as series regulator (IRF820 / IRF840, cannot remember which one). The tubes worked as reference. So you can take a semiconductor voltage regulator and use the tube instead of a zener. Be carefull with the size of the capacitor across the gas tube otherwise it becomes an oscillator.

I use Duncan Amp pages ' PSU designer II to work out the currents through the rectifier tubes / transformer windings to determine maximum currents.