"Phil Nelson" wrote in message
...
all tubes tested before starting work, but this one
croaked sometime during repairs.

I just picked up on this thread and read it with interest.
Sounds like you're on the right track. That's a nice
receiver when working correctly.

One thing I'm beginning to appreciate about fixing old
radios & TVs is that some components which test "good" or
seem acceptable at first, may decide to give out after a
few more hours of operation. The tube (or whatever) may
simply have reached the end of its service life, or
perhaps it croaked after running at full power for the
first time in decades.

Before I declare victory on any project, I run it on the
workbench for some hours. Much better to find and correct
those latent issues now, rather than later.

Have fun,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Its possible for tubes to have bad seals or very slight
cracks that allow some air to get in. The "getter", which is
the silver stuff on the inside, can absorb only so much air
after which the tube will simply not operate. Sometimes the
symptom is a blue glow inside the tube, something like the
glow in a voltage regulator tube. This should not be
confused with the slight dark blue glow somtimes seen in
beam power tubes with very high voltage on the plates. This
is not due to air and is normal.
It is also pretty common for resistors and, especially
capacitors, to die after being unused for a long time. There
are many causes, moisture absorption and others. Even
transformers may die shortly after being fired up after
being unused for a long time.
A useful tool when working on old equipment is a metered
variable transformer. Ideally, it should have both a voltage
and current meter on the output. The current meter is
especially important since it will show excessive current
before damage is done. My suggestion is to remove rectifier
tubes from the equipment and bring it up slowly on the
transformer. If there is any sign of excessive current turn
it off immediately. If it looks OK this way try again with
the rectifiers, again bringing the voltage up slowly. Of
course, the filter capacitors should be checked first for
shorts.
Most electronic equpment likes to run. Leaving it off and
in storage for long periods is not good for it. I suspect
nearly everyone who follows this group already knows all
this stuff.


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Richard Knoppow
Los Angeles, CA, USA