21 Jun
2012
21 Jun
'12
10:17 p.m.
From: ard at p850ug1.demon.co.uk
Subject: Re: Weird Prices on E-Bay
To: cctalk at classiccmp.org
Date: Thu, 21 Jun 2012 19:30:26 +0100
[...]
-snip-- It is interesting that the amplifiers in the 135 does use a nuvister
tubefor the first stage. After that, it does several stages of differential
transistorsinto a transformer to drive the final transistors. Mercury cells were my
primary source of mercury when I was a kidI used to scrounge the trash behind the local
radio/electronics shop.The service hundreds of hearing aids. Contrary to what most think,
it isn't real dangerous until combined intoorganic compounds. Of course, constant
breathing vapors isn't to good( As mad as a Hatter ).Dwight
ll no longer need to do this.It is interesting=2C
how it works though. Inst=
ead of a DC servo motor=2Cit uses an AC synchro motor. It chops the error s=
ignal and uses thatto drive the motor. A clever way to avoid DC offset with=
That was not at all uncommon in ploters (and chart recorders) using
valve amplifiers (a 'chart recorder' here is a device with one
votlage-cotnroled axis (moving the pen across the papar) and one time
axis (moving the paper at a constant speed using a synchronos motor and
gearbox).
WHt was often done in such unts was to take the DC error voltage optained
by the differnece between the input nad the slidewire position. THis was
then choppend by a vibrating reed device eneerginsed from the heater
winding (normlally). The resulting signal conld then be amplifieed in a
normal AC-coupled valve amplifier. The amplitude of the output was then
the magnitude of the eorror (and thus couple be used to cotnrol the speed
of the motor), wehter it was in phase or anitphase iwth the heater
winding gave the direction. The output of said amplifier drove one
winding of a 2 phase motor, the other widing being mains-supplied (maybe
from a transformer winging).