Chris Morriss wrote:

The latest bifilar-wound 1:1 interstage from Sowter would be a good
choice. I've still got my DA100 triodes and the Sowter OPTs I had wound
many years ago, and a rebuild using a good interstage transformer would
be of interest.

The drive requirements of an 845 are near as dammit the same as the
DA100 (once described by Hi-Fi World as 'The Aston Martin of British
power triodes'!).

A 12B4 driver transformer coupled will do the job, but a little B9A 12B4
looks dreadfully weedy against a DA100. (Or an 845)


I am currently very fond of the 6em7 as a gain and driver stage, very
similar to a 6sn7 - 2a3 combination.

--
Nick