"Phil Allison" wrote in message
...
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.



I remember that from the 60's. In the Music Room the teacher used to
play us records with an old E.A.R. record player with valve amp
feeding what I guess was maybe a 8inch or 10 inch loudspeaker mounted
in the centre of a (quite solid) baffle board about 4ft or so square.
I can still hear it in my minds eye (as it were) to this day - and it
makes me smile.


--
Woody

harrogate3 at ntlworld dot com