Don't go too crazy replacing tubes. More often that not, a tube is still quite
good after years of use. Assuming that the filaments are wired in parallel,
plug one tube into the amp at a time, key the amp and monitor quiescent plate
current. The resting current should be within 20% of the group mean. If you
have an assortment of tubes, I would match them for resting current (again,
checking them one at a time assuming filaments are parallel connected). If you
have an extreme outlier that has low resting current, I would suspect that it
is weak. Use tubes with similar gain together. The RF transistor industry
used to do this by marking BJTs with an ink to indicate Beta grouping.
I would pull a leakage current check on HV caps. You can do that by putting a
10K ohm resistor in series with a single silicon diode (1N400x) and hook up to
110VAC (one cap at a time). The cap should charge, then not take more than a
few microamps thereafter. Measure the voltage drop accross the resistor; it
should be nil. I find that many caps in old amplifiers leak and require
Replace any and all heat damaged components such as resistors and caps. Check
that variable cap plates are parallel. Replace noisy fans. Clean old grease
Check the bandswitch. If there are broken or burnt contacts, replace it. If
the position stays are worn, replace it too. There is nothing more annoying
than a flaky bandswitch. You can buy silver solder and liquid flux from
various vendors on line.
Check to make sure that all solder connections are intact. I find many
corroded and defective joints in amplifiers. Use liquid flux which will help
clean crud and allow using less heat than without flux.
That's about it. You have a simple amplifier so that this should be pretty
easy. Good luck,
----- Original Message -----
From: "John." <email@example.com>
Sent: Tuesday, July 10, 2007 10:40:53 AM (GMT-0600) America/Chicago
Subject: [Amps] Clippertion L 572B tubes
I am in the process of restoring a Clippertion L amp. Any thing that I
should look at that has been a problem ?
Looking for some good 572B's pulls or something like that. Need 4.
If one could be found then I could start testing the amp.
Thanks de John KÃCQW
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