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In Reply to: 2 Stage 6C45 Amp posted by Merak on August 12, 2005 at 11:59:16:
It's been a while since I've re-measured/calculated anything on the amp, but if memory serves the 6C45Pi is running -around- 40Ma with about -1.5v NGV. This rings a bell also, since I've considered battery bias (single cell at around 1.3v - 1.5v) but I haven't implemented that yet. On the schematic, ignore the 320v spec on the input of the choke load, that was a mis-measure; I believe it was closer to 220v.
I have no idea off the top what the Mu was/is, but I can state the 6C45 tubes themselves vary quite a bit; I have bought about 10 of them over time and use the amp and a scope to "pair match" them for gain, which is of some importance especially since my pre doesn't have a balance control.
I started with resistive loading on the driver, moved to choke loading (definitely better). I tried IT coupling between the driver and output, but the IT's I had on hand weren't really up to the task, so back to cap coupled. I suspect high quality IT's would be a plus overall.
As to speakers, at the beginning I was using Celestion SL-600's (not a SET friendly speaker from a sensitivity standpoint - 82db 1W/1M, but at least they present a stable impedance/load across the bandwidth), but for the last year I've been running them on a DIY set of Bastani Prometheus (Mk1) Open Baffles w/subs, with great results (http://www.bastanis.de/diy/prometheus+mkii_en.htm). I've also listened to them on Cain and Cain Abby's and some various horn speakers. Always got positive opinions in listening sessions!
The sound is very "neutral", not overly warm but at the same time not clinical/sterile either. Still seems to present the "SET magic" most everyone appreciates.
I also used ultrasonic AC for the 211 filaments; I like the results and total lack of hum.
Future experiments will include battery bias on the driver, high quality IT's, and -maybe- a 2 stage driver utilizing a 45 to drive the 211, but not due to any dissapointment over the initial choice of the 6C45...
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Follow Ups
- Re: 2 Stage 6C45 Amp - mrfixit 08:01:50 08/17/05 (2)
- Re: 2 Stage 6C45 Amp - Merak 06:15:49 08/18/05 (1)
- Re: 2 Stage 6C45 Amp - mrfixit 04:54:15 08/19/05 (0)
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