[Boatanchors] Water, Water Everywhere.

[Brian]

Hello Dave,

Grime of the ancient mariner?

Let's consider the chemistry of water.

Water is generally non-conductive - it ionises to the extent of 10^-7. 
Remember your school days' chemistry classes, and a pH of 7? (negative 
logarithm to the base 10, of hydrogen ion concentration)
If the water has taken up metallic salts, these may ionise to make a 
conductive electrolyte; for instance, sulfur in the air can combine with 
water to form sulfurous acid, which then gently eats bare copper to form 
bluey-green copper sulfate - which, when wet can become moderately 
conductive, leading to unwanted short-circuiting. The sulfur comes from the 
exhaust of motor vehicles. Eventually, the conductive path of the copper 
gets eaten away and goes open-circuit. This can be repaired on the outside 
of coils, eg, the terminations.

Some 'plastics', eg, bakelite and other phenolic resins that have been used 
to make coil formers, gradually lose whatever water was in them, and shrink. 
If the copper wire used in the windings was not insulated, then you may get 
shorted turns, which can be intermittent. Even Nylon shrinks over time. If 
the turns are held in place with some form of glyptol, then shrinkage 
shouldn't be a problem because the dissipation factor of the glyptol will 
have been taken into account at the design stage. (Pigs might fly?) If you 
anticipate your drying efforts may result in shrinkage of formers, it may be 
wise to coat the windings in a low dissipation factor varnish. If the 
varnish has an appreciable dissipation factor, then the inductance of the 
coil will increase. I use nail varnish painted on in three or four stripes 
to retain integrity of the coil form, but to have minimal effect on 
inductance if the coil former shrinks.

All chemical processes proceed faster when the temperature is raised. 
However, paper can spontaneously combust when the temperature exceeds 40 C, 
ie, about 104 F. Water at any temperature above 0 C, ie, 32 F, has a 
positive water vapour pressure; that is, it evaporates. So, if all you want 
to do is drive off water before all the other nasty things happen, put it in 
a warm, dry environment. At low temperature, water removal may take weeks. 
Avoid using a household oven: the temperature excursion before operation of 
the oven's thermostat is OK for food processing, but may exceed 'comfort' 
for electronics. Incandescent lamps (remember them??) will give gentle 
heating, but you have no control over temperature or humidity - the external 
bulb of the lamp can easily reach 250 C, ie, about 480 F. If you don't have 
an hygrometer, a simple means of checking humidity is to put a potted plant 
in the same environment and measure the resistance between two embedded bare 
wires. A $2-shop max-min thermometer is a good investment - use it later 
where you store your 'sleeping' BAs.

If there has been breakdown accompanied by arcing, leading to carbonisation, 
there is no simple chemical reversal of that. You will need to use 
mechanical scrubbing, eg, a small Dremel bit.

73 de Brian, VK2GCE.


On Saturday, December 12, 2015 3:43 AM , you asked:

Many of our beloved old radios have been sitting, cold
and quiet for many decades.
Some of them getting close to a century.
Recently, I've been dealing with bakelite and phenolic
in our sets which have taken-up moisture over the
years.  Right now on the bench I have a TCS
receiver in which one of the pins of Z202, an IF
transformer, is leaking B+ to ground through
the phenolic.  Pulling an IF from a TCS is a pain
but do-able.
So may we discuss ways to gently drive moisture
from our sets?  I can "get rough" in the stove with
those bakelite inserts in WWII radio connectors but
that won't do for a whole set.  I've tried powering
just the filaments and leaving a set for a couple of
days but I don't think they get hot enough to do much
good.  Heat lamps can do some damage.
What have you done?    I'm thinking of light bulbs
with the radio in a thick cardboard box, *outside* in
case the box decides to catch fire or something.

73 Dave AB5S