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Yes - filament bias on outputs doesn't go much beyond 4P1Ls

Posted by andy evans on July 11, 2015 at 06:59:56:
I always wanted my output stage in filament bias, and didn't achieve this until I hit on PSE 4P1Ls. The thing is that you need quite a low bias voltage. Maybe 10Y is another possibility. There's not much else I can think of. Bias voltage on 2a3 and 300b is too high - the demands on filament bias would be ridiculous.

But 4P1Ls work like a charm. I have 2 of them in parallel, but 3 in parallel is quite do-able.