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In Reply to: RE: Neither posted by drlowmu on January 22, 2012 at 23:48:56
if you are DIY'ing, go for direct coupling. there is no way that any cap or IT can be better than 2 or 3 inches of wire.
Provide negative voltage for driver to zero your final's grid
Yes, direct coupled should be the way to go. Either stacked PS or like the DRD.
I heard different story, some says direct coupled need a stiff power supply with regulator. Even with 300B low powered, like the DRD, the B+ voltage will be the sum of driver + output. Now we are talking about 500+V. Regardless of big triode in DRD, almost impossible!! This is pretty tuffy to have a regulated power supply for DRD.
Another approach by talking to several tube builders and they prefer 50 or 70% more AC voltage on the secondary than the acutal B+ voltage and very low DCR secondary winding as well. Then drop the voltage from the first cap for actual needs feeding the low DCR & high inductance choke along with big bank of reservoir for proper filtering. This is the only way making a PS for a direct couple SE amplifier like the DRD. What do you think?
You state this :
"This is the only way making a PS for a direct couple SE amplifier like the DRD. What do you think? "
1What do I think?? Ha, you asked the right guy!
"This is the ABSOLUTE POOR WAY of way making a PS for a direct couple SE amplifier like the DRD. " No good.
Thats what I think .
I don't do DRD, don't want the cap in there where it is. I can do a Rk cap better than most, so its no problem for me. I prefer a simple a circuit as possible, Loftin White amps hold my interest the most. I prefer conservative tube dissipations and want ultra reliability to my builds.
I used to always regulate B+, no more. I like dual rectifier tubes and well-designed "modern" L1/C1/L2/C2 filters to the Finals.
A 2A3 DC amp needs 480 to 490 VDC of B+. A 6AQ5 DC amp (lower power) needs about 430 VDC. As for power supplies, email me privately with your own email address, and I will send you a couple of great papers as attachments, on what we are doing now a days, which is quite different from what you are thinking. Address above. Read them over, then ask questions !
At first I had problems with bias drifting along with the line voltage drifts. I am using stacked supplies so when B+ drifts with the line voltage the bias drifts.
Solution, use an AC regenerator. I bought a Crown pro audio 600W amp on sale, a low distortion sine wave generator, and a 3:1 power transformer hooked up backwards to the speaker outputs on the Crown to get a very stable, very clean, 120VAC. Added benefit you can control B+ and play with varying the input frequency.
I know there are off the shelf solutions but that's no fun and more expensive.
Oh, I can't generate enough juice to run the filaments too so they run off their own transformers hooked to the wall, not the regenrator.
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