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In Reply to: Re: What's wrong with the C-47U? posted by Perseo on March 11, 2007 at 14:57:01:
0.5V is too high for a single-ended triode - about 20 mV p-p to an 8 ohm speaker - but it might be OK for a pentode or push pull. Try it and see - but be sure you have room for more filtering if necessary.
Follow Ups:
Hi Tom,Well, thats only your opinion and not mine, now a days Tom, on an output stage.
You have not experienced this type of supply, have you ? You should !! We use 105 dB RCA FC's and about 98 dB Altec 515s at Greg's house, and have no problem.
My favorite filter ( so far ), has been two-stage, not three, because of the blinding instantaneous speed and timing the two stage gives. Filter it some more, put in five stages if you want, and you will wonder where the music went as far as both timing and dynamics !! A higher number of filter sections will be, by comparison, all askew and out of kilter and out of time. What happened to the music ???
Front end supply, with the same basic two-stage filter, and less draw, is 20 mVAC.
Funny we should have this discussion Tom, over the past, for 25 years, I would actively tube regulate, TWO regulators in series with a draw down power R between them !!, to get low ripple, usually 1 mVAC in my triode amps.
I really like this new-to-me Low C, HY and DCR unregulated approach, as no real comparison to anything else in audio that I know of exists today - IMHO.
I'm workin on mine! I need to build a separate front end supply though.
I'm putting together the main B+ now, for the output stage (2A3). I thought I would need "less" ripple on the driver? Can I use a similar two stage low everything supply and not have noise on my front end?
I was going to use a low mu triode: 6P5, 6J5 or better (IMHO) triode wired C3o which has a Rp of 2K while mu of 17, (the 6J5 we should have had). I have some 1660 IT's, also plate chokes, assuming only these two coupling methods would work with this PS? I guess loading the driver with a resistor "kills" the point of the PS? Jeff, please tell more about your driver and the problem solving you went through thanks.
Hi bobbij,Read my prior post, only 20 mVAC to the 76 stage, with a two stage filter, so YES, do it the same for your front end. Use a Mills MRA-12 ( one or more ) shunt bleed across the B+. No problem. Use a real triode !!
No, loading the plate with a good resistor is fine, and is wider band than any choke or IT.
Thanks Jeff, OK, I thought the BW was "wider" with a resistor, but wasn't sure the dcr was contrary to the rest of the effort. I too, like the "idea" of "pure" triodes. I like 6p5, 6j5, etc...But the C3o is a surprising devise, a little on the bright side, perhaps due to the low Rp. Now, to load a 6P5 "properly" I'm assuming a 50K plate resistor, so I'll have a 250V drop at 5ma idle current, so I'd need at least 450-500 VDC to start with?
Hi,
Please kindly re-read Dennis' comments in my post of his most recent two emails, where he clarifies and refines this subject, second email, under point ( H ).Design with low DCR except for the audio circuit, there, High DCR to allow it to swing !!
Got it ??!! URL follows.
Jeff Medwin
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