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05-07-2023, 04:51 PM
Hi Guys
The old 20W amps were fixed-biased. Definitely use two bias pots for your 2x EL84 amp, then you can set how hot they run and what tone they produce (within the limits of the tube for both). Apart from being able to get more life out of the tubes and potentially eliminate the mud that comes with cathode-bias heat, the output stage can be hum-balanced, which is different than DC balance.
In fixed-bias push-pull there should always be separate bias pots for the push and pull sides. This is generally better and easier to configure than using a bias + balance pot, as TUTs show. I have to admit that early on I was enamoured with the latter but found later that the separate bias pots is a lot easier to deal with in every way.
Have fun
The old 20W amps were fixed-biased. Definitely use two bias pots for your 2x EL84 amp, then you can set how hot they run and what tone they produce (within the limits of the tube for both). Apart from being able to get more life out of the tubes and potentially eliminate the mud that comes with cathode-bias heat, the output stage can be hum-balanced, which is different than DC balance.
In fixed-bias push-pull there should always be separate bias pots for the push and pull sides. This is generally better and easier to configure than using a bias + balance pot, as TUTs show. I have to admit that early on I was enamoured with the latter but found later that the separate bias pots is a lot easier to deal with in every way.
Have fun
