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4P1L in filament bias

4P1L is a great tube in triode. Run the filaments in parallel at 2v and use filament bias with a couple of Rod Coleman regs (Google Lyrima). Separate transformers for each tube and preferably a nice Hammond choke input. I use 159ZC. It's worth paying a lot of attention to the filament supply - in filament bias it makes a big difference. No false economies. Look at Ale Moglia's site for details.

Plenty of old stock of 4P1Ls, cheap and rugged as hell. Rp of 2k and mu of 11. What's not to like. Needs to be run at 25-30mA. Ale, myself and several others stopped using 26s in favour of the 4P1L, especially as a driver. It's an extraordinary little tube. To get the best out of it you must use filament bias. Threads on DIY Audio, both as a line stage and as a SET. I use it in the output stage in preference to 300b or 45. Just sounds better to me in filament bias - no cathode bypass caps, just a small resistor. Makes all the difference.

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