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12bh7

I have never used a 12BH7 before.

Two questions:

1) In Urei LA2 they use a 12BH7 in the output drive section instead of 12AX7(more gain I know) or 12AU7, why is that?

2) Other that the heater current, what is the difference between a 12AU7 and 12BH7?

Thanks!

Sound Workshop Series 40 Schematics mixers with vertical indicator

I address to engineers and technical experts: please, help to find schematics of Series 40 mixers with vertical indicators (what gathered in the USA in 80, from a brand Otari). I have found all schematics - 1280, Series 20, 30&34. But Series 40 schematics is not anywhere! I thank for any help!

volume pedal

I am looking at a midi device that will take controller msgs from my pedal board expression pedals and convert them to resistance outputs in the fashion of a potentiometer. I want to use that resistance as a volume controller between my keyboard and amp.

I am concerned that the potentiometer will be, by design, linearly scaled, and not as db audio taper.