78 Tubes covered with wax - What should I do about this?
Description
This article is from the Antique Radios And Phonographs FAQ, by Hank van Cleef vancleef@netcom with numerous contributions by others.
78 Tubes covered with wax - What should I do about this?
My old radio has a lot of tubes covered with wax, and some of the wax
has melted out and is on the bottom of the cabinet. What should I do
about this.
These are inexpensive wax-impregnated paper-dielectric
capacitors. They were notorious, even when fairly new, for developing
opens, shorts, intermittents, high dissipation, and tend to be rather
fragile as well, particularly when soldering around them. Melted-out
wax is common, and may be only the result of heat developed under a
chassis in normal operation. From reliability and other engineering
points of view, replacing all of them with newer capacitors of other
types is part of a refurbishment/overhaul. Some collectors feel that
40-60 year old capacitors are "survivors," that wholesale replacement is
unwarranted. Also, there are two schools of thought on replacing
components with others that are very dissimilar-looking, even in areas
that are not normally visible when a radio is installed in its cabinet.
A few restorers go so far as to melt the wax out of old capacitors,
remove the foil-paper "innards," install a new capacitor, and refill the
body with wax. Other restorers feel just as strongly that consistent
appearance is more important, and that 100% replacement with no attempt
to disguise the appearance of new components is to be preferred. Alfred
Ghirardi, in "Radio Physics Course," has a lengthy discussion of
failure modes of these capacitors, and states an expected service life
of 10,000 operating hours.
Whether to do a wholesale replacement or not is a decision
you'll have to make yourself, and whether to use modern radial-lead
components or to try to find lookalike replacements or disguise the new
ones, also has no uniform consensus. Your radio may not give you much
choice about wholesale replacement. If you find more than one or two
bad ones, or if the set has mysterious ills, parasitics, or poor
performance, or is intermittent, 100% replacement is indicated. If the
item you are repairing is "blue collar" or "high tech," 100% replacement
with obviously new good-quality components seems to be preferable. By
"blue collar," I refer to test equipment and items such as Hammond
organs and studio equipment that worked for a living. By "high tech," I
mean good communications receivers and genuine high-fidelity equipment.
Many of these items used higher quality components originally.
One item that has complete consensus is quality of workmanship.
You will want to learn how to remove component leads completely, clean
up old terminals, and make neat new solder joints.
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