Type 80 rectifier.
A bad rectifier will result in lower plate current, visible on the meter. However a
rectifier that will supply enough stand-by current may still be not good, since the amplifier circuit is
auto bias, and very good quality, new 45 tubes can compensate that for some part. So they will still
run close to 32mA, but plate voltage is too low. Obviously best sound can not result this way. So
make sure you have at least one known to be really unused, NOS Type 80 rectifier, and compare any
unknown rectifiers with this. So compare the meter readings, and compare the dynamics of the sound
at high volume. With some experience, you can easily pick out a weak rectifier like this.
Unfortunately unused (NOS) Type 80 and 717A are getting scarce now, but good tubes will serve a
long time. Note: Testing of rectifiers can not be done very reliable on a Hickok tester, though this is
the mostly used tester for USA tubes. So readings on a Hickok must be very strong, to be sure. Best
tube tester for the 80 are the AVO's (Mk2 or higher) or the Russian L3.
Service, Repairs and technical issues.
This should only be done by a qualified high voltage technician.
There are no parts inside that
need service or adjustment, though it is always a good idea with anybrand tube amplifier to check it
from the inside
latest
after 10 years. Do a careful visual inspection of all components, and re-tighten
all screws moderately so good ground connections are still present. It is amazing to see sometimes that
tube amplifiers are constructed such that this is impossible. Not so with the A08-S! The bottom cover
of the A08-S is one single piece, and when it is removed, all parts can be very conveniently reached
even from the sides, for service or repairs. Though perhaps not important when new, your service
technician will be satisfied to see how convenient it is, to work an the A08-S.
Transformer caps
:
The transformer caps need never be removed, also
not for checking up. However if you whish to do
so, do not remove the screws that you see from the
outside. For removal of the cap, take off the
amplifier bottom, and then from the inside remove
the four large black screws. This will remove the
whole cap unit with just four screws. Before you
do, mark the back of the cap. If you forget this, you
might put back on the cap reversed, and the screws
may not fit.
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