Andy Evans wrote:

I'm building a PP 2a3 amp right now and haven't decided on the input
stage. I'd like to use 6J5G and/or 1626 valves. Open to other
suggestions, but like to keep to octal or UX5 types (I also have 76,
37, 56, 27). I'd also need a differential first stage for the option of
balanced or SE, and I have CCSs. 2a3 needs about -50v of bias. Ideas?
ANdy

There must be 100 different ways to drive a pair of 2A3 in PP.
You will need around 37Vrms applied to each grid so the drive amp
should have ability for 70Vrms if possible.
To do that with an LTP using a pair of 6J5 is OK, and the input
stage/driver amp
that is shown at the 50/50 amp details below could be used.
http://www.turneraudio.com.au/htmlwe...0ulabinteg.htm
I used 6CG7 = 6SN7 = 2 x 6J5.

Some folks would buy a decent IST and simply use a 6V6 or EL34 in triode
to drive the primary
and use the 1:2 step up to drive the 2A3 grids directly, with each 1/2
secondary
taken to separate low R value bias pots.
But if its mainly class A then cathode biasing is OK, and the IDST sec set
up as a
grounded CT winding.

With RL = 4k a-a, and a sec load of 4 ohms, and with Ea = 350V, Ia = 40mA,

PO = nearly 20 watts AB with a few watts of class A.
With 8ka-a to 8 ohms, PO = 15 watts, nearly all class A.

Rout will be about 2 ohms including tranny winding losses
and without global NFB.

Patrick Turner.