Don Pearce wrote:

Jim Lesurf

Just to let people know I've added some examples to the 'valve era' page at

http://www.audiomisc.co.uk/Armstrong.../ValveEra.html

Jim

Just had a quick skim. Did I read that right? You have to buy and fit
your own output transformer. If that is really so, I can see why there
is no overall NFB.



** The EXP48 output stage uses a pair of 6F6 pentodes operating essentially in class A, so has low distortion without NFB.

However the output impedance is high, providing current drive to the speaker.
The gain of such a stage follows the speaker's impedance, rising strongly at bass resonance and also at frequencies above 1kHz due to voice coil inductance.

With typical speakers of the time, mounted on an open baffle, this gave the resulting sound an automatic eq that was quite intentional.

Note the lack of any form of tone control.



..... Phil