Aug - AmericanRadioHistory.Com

just doesn't have the sock it once did,
or spills over, or sounds muddy.
Since every power amplifier worthy
of the name is a push -pull unit, and
since balance between the two sides is
the requisite for proper operation, you
can make the following deductions. If
distortion is very high, one side may
be completely "out"- dead. If the
main fault is lack of impact, aging may
have impaired the condition of both
tubes. An amplifier can go unbalanced
because tubes, resistors, or condensers
deteriorate. Total power output can go
down because the rectifier or output
tubes wear down. The most common
causative factor is tubes -and these
are your great weapon in your home
fight against deterioration.
Since the "Williamson" revolution,
many power amplifiers use the same
tube types through the early stages
(up to the output tubes, which are
bigger and near one end of the amplifier,
generally). Working on our
theories, try the following; you are
cautioned in all cases to look before
you plug in, to protect your hands
from heat before you grab, and to use
your head:
I. Listening to music at moderate
room volume, pull out one output
tube. If no change in sound
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product of the
Butish industries Group
AUGUST 1955
either that tube or one of those
before it in the circuit is dead.
If the sound goes out completely,
then the other output tube or one
before it on the other side of the
circuit is dead. On general principles,
buy a new set of matched
output tubes, and put them in.
2. If no improvement from (1 ),
and your circuit is a Williamson
or similar type, move the driver
tube ( little tube nearest the output
tubes ) into the first tube
position ( make sure it is the
same tube type). If circuit goes
dead, replace the rube you just
moved up front. If sound goes
worse, replace the tube you just
moved in the driver position.
3. If the tubes just before the output
stage are in separate envelopes
(cf. the Fisher goA ), reverse
them and listen for improvement
or degradation in quality.
4. Reverse output tubes and listen
critically to the bass region. Use
program material such as organ,
played at moderate or soft levels.
Where the organ is deeper and
smoother, you have the best -balanced
condition. Or try the same,
turning the output balance-con-
Continued on next have
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