In Reply to: Another Option posted by Triode_Kingdom on September 12, 2014 at 22:22:16:
The 4P1L is microphonic. This matters in small signal positions, but you can pretty much forget it if you have 2v in IF, and this is a definite if:
- you starve the filament a little. I run parallel filaments at 1.9v or 2v.
- you have a heavy and robust chassis. I'm talking 4mm aluminium top plate.
What you want to avoid is a flimsy steel chassis. I have 2v in from my DAC and I'm good with a 2 stage amp - 4P1L into PSE 4P1L. No suspended sockets or rubber decoupling, but a solid chassis.
I realise Jeff has his own way of doing things. Otherwise I would strongly suggest filament bias. Small cathode resistor like 10-20 ohms. No cathode bypass caps. Rod Coleman filament boards, really good filament supply e.g. choke input. One of these to each tube. A lot of care goes into the filaments - and better to use an outboard power supply. Interstage coupling with a really good interstage. Very simple circuit, but quite a big build with all the filament supplies.
I've never heard of AC filaments for the 4P1L. Even if you want to direct couple, be sensible and get some Rod Coleman boards. We've been working on this for years with the 26 as the initial tube and there are monster threads on DIY Audio on both tubes. The knowledge is well advanced and many are building with them and loving it.
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Follow Ups
- How to use the 4P1L - andy evans 02:46:08 09/13/14 (15)
- RE: How to use the 4P1L - drlowmu 08:29:16 09/13/14 (14)
- RE: How to use the 4P1L - andy evans 12:59:06 09/13/14 (0)
- RE: How to use the 4P1L - Al Noakes 10:10:42 09/13/14 (12)
- RE: How to use the 4P1L - drlowmu 08:40:47 09/15/14 (11)
- 4P1L schematic - andy evans 03:28:31 09/16/14 (10)
- Its getting worse !! - drlowmu 08:58:52 09/16/14 (9)
- I don't think so at all.... - andy evans 18:55:14 09/16/14 (8)
- RE: I don't think so at all.... - drlowmu 09:46:11 09/17/14 (7)
- What's smart 845? - andy evans 10:20:32 09/17/14 (6)
- RE: What's smart 845? - smart845 09:35:41 09/19/14 (0)
- Who - Tre' 17:37:20 09/17/14 (4)
- I thought Who was on first base..... ? - andy evans 06:13:22 09/18/14 (3)
- I don't know. - Tre' 10:37:52 09/18/14 (2)
- RE: I don't know. - smart845 09:57:32 09/19/14 (1)
- RE: I don't know. - andy evans 08:32:22 09/20/14 (0)