Iain M Churches wrote:


Hmm. That's interesting. I think that the front end is two
halves of a 6SN7. It is difficult to say, but I think we were
listening at perhaps only 3-5W.
There was no audibler distortion (or at least none that
I could detect:-) at this level.

No I wouldn't expect you would hear any distortion from a 211 at those
sorts of levels.

211's are quite easy to drive in A1, as they have quite a high mu. But
if you look at their curves they are meant to be used in A2, so are
often driven by a cathode follower.

My plan involves using a 2a3 to drive the 211 via a 1:1 interstage, so I
should be able to have some a2 operation if I need. The 2a3 (current
plan) will be using a 6sn7 in a direct reactance drive sort of
arrangement, or maybe normal DC coupling, depends on how the DRD works
out. Seems fine in Spice, but the reality may be different...



211's are very dependednt on transformer quality, the high Ra, means that
you can have HF problems if its not a well made (expensive) transformer.


I listened carefully to the 1st violin. It was perfectly clean. The
limited lower range of the cello did not give me a chance to
evaluate the LF performace of the amplifier. The transformer was,
I assume, Russian made.

Well, LF, tends to be ok, as to handle to 1200v at 70ma that a 211 would
normally be working at, you tend to have a lot of iron to avoid
satuartion. Its the HF thats the challange for the winder, the 10K or
higher primary load that a 211 needs means you need good design to avoid
lots of parisitic capacitance, and combined with the high impedance that
will limit your HF response.

--
Nick