In Reply to: RE: in most usage where the dissipation is low 6CG7s should sound just like a 6SN7 posted by Blackdog on October 17, 2015 at 16:03:09:
If you have read the data sheets you ought to have noticed that. Look at the transfer curves?http://www.audioasylum.com/audio/tubes/messages/26/262921.html
http://www.audioasylum.com/cgi/t.mpl?f=tubes&m=264422
http://www.audioasylum.com/cgi/t.mpl?f=tubes&m=264409
http://www.audioasylum.com/cgi/t.mpl?f=tubes&m=260468
http://www.audioasylum.com/cgi/t.mpl?f=tubes&m=259993
When used as a cathode or concertina phase splitter they are all but blameless, but that's with 100% local negative feedback.
Do a bit of digging and I'm reasonably sure you will find that the 12AU7 does have RF antecedents.
When I first got into audio - as an idea - it was via getting to know recording engineers for our national broadcaster - down here in Aus. - who would often record the cathedral choir I sang in, with just one single-capsule stereo-mike. I was a tween at the time.
Valves ruled back then, and DIY too, and I don't recall anyone telling me how wonderful a 12AU7 was as a gain valve. All who commented said what I am saying.
The 12AU7 is/was used by mfrs because its current draw is low and thus the PT doesn't have to be so expensive. It's strange fame with rollers may also contribute to its ongoing use.
Nevertheless this is a perfectionist hobby, and keeping overall/total NFB down is a pretty good idea, no?
But, using a 12AU7 for gain duties means extra NFB.
My current (version 10 ???) pre-amp still (since v3) uses a 12AU7 at the output, it's currently a selected Brimar 13D5 but it's in CF line-driver role. Good economical choice.
If I ever do build with a balanced output stage I might just double up but add CCS's under each valve.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
Edits: 10/17/15 10/17/15
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Follow Ups
- Sorry no, its designed in distortion numbers are quite poor - Timbo in Oz 20:19:16 10/17/15 (4)
- Never seen a 12AU7 in an RF circuit - Ralph 09:22:03 10/19/15 (0)
- RE: Sorry no, its designed in distortion numbers are quite poor - Blackdog 20:41:11 10/17/15 (2)
- RE: Sorry no, its designed in distortion numbers are quite poor - Lew 08:41:33 10/19/15 (0)
- I don't buy new, I now just upgrade / rethink vintage stuff. - Timbo in Oz 20:51:31 10/17/15 (0)