[Hallicrafters] Re: [Hallicrafters]V4#448-Dampp Chaser II

[Phil Barnes-Roberts AD6PQ]

At 04:05 AM 2/5/04 -0500, hallicrafters-request at mailman.qth.net juggled the 
keys to produce...
{snip}
>Message: 2
>Date: Wed, 4 Feb 2004 20:33:08 -0800 (PST)
>From: Wayne Light <hwlight at sbcglobal.net>
>To: hallicrafters at mailman.qth.net
>Subject: [Hallicrafters] Dampp Chaser II
>
>Several of the guys on this list have written and asked about the 
>responses I received regarding the use of this device in some of the 
>Hallicrafters Radios (SX-101, etc.). I thought I would respond this way, 
>since there may be others that didn't write and are interested.
>
>The majority of the responses, from the experts, agreed that Hallicrafters 
>put this resistor there to keep the oscillator section warm and therefore 
>more stable...so when the radio was turned on, there would not be a 
>significant change in temperature.  Only one thought it was actually used 
>to keep the dampness out of the radio.  This little resistor is "in line" 
>even when the radio is off and constantly gives off a little heat (of 
>course, the radio must be plugged in :).
>
>The one I have in my SX-101 seems to be working, so I have not tried to 
>find a replacement.  Several people wanted to know if there was anyplace 
>to buy a NOS for this unit.  If anyone knows of a replacement source, 
>please let the group know.
>
>Thanks again for all that responded!
>
>Wayne
{snip}

I agree with the temperature-regulation rationale; sorta like a crystal in 
an "oven" - a heated holder.  As for replacing one...

Actually, something like the Dale aluminum-bodied "Quonset-hut"-looking 
resistors comes to mind.  They can be bolted to a heat sink or chassis 
plate (with small, 2-56 hardware).  Of course the Ohmite Brown Devil 
tubular style would work, as long as you put the holders on it at each end, 
to keep it in place.  Just about anything with about the right values, and 
mounted safely -- unless you just gotta have authentic NOS.  Sorry, no 
clues here either.

For the resistance and power value, someone had mentioned 8W; across 
120VAC, P=V^2/R, so R=V^2/P or (120)^2/8 = 14400/8 = 1800 ohms.  Anything 
fairly close should do, 1500 to 2200 ohms, say, and derate it for a good 
full-time safety margin, maybe a 20 or 25W unit.

Any distributor, Mouser, Digi-Key, Newark and Allied etc. will have 
something good, and Rat Shack will have a cheap Chinese (sorry; redundant) 
knock-off of a real part that you'll spend all evening trying to get solder 
to stick to.  Before Chinese-Americans object, many of those parts may 
actually come from Taiwan, Singapore, Malaysia, etc. -- but the cheap stuff 
still sucks equal-opportunity bad.  Good connectors and other parts can be 
found, at the above distributors, and they work and don't melt on 
you.  (Sorry-- flashback to bad experiences with RS parts.  Time for my meds.)

Historical Note:
And yes, there was a time early in, and before, WW-II when gear going to 
the tropics had a terrible problem with mildew.  It got into switches and 
pots, and made life miserable for everyone.  That was the origin of the 
Dampp-Chaser.  Later, the military and contractors found anti-mildew 
varnishes that were slathered on just about anything (like the ARC-5's and 
other surplus we saw in the Fifties and Sixties - that's why they look like 
that, and are so hard to solder.  You have to melt - or pick off - the 
varnish first!)

Later, in Vietnam, we kept the civilian Collins S-Lines and Henry linears 
in air-conditioned rooms (well, MARS did - good excuse, field ops was 
another story, not mine to tell.)  But we did put 40-60W light bulbs in the 
bottom of our wall lockers, on full-time, which kept clothes above the dew 
point - most of the time.  When the rain came down in a wall of water, 
_nothing_ stayed dry.

Semper Fi and-
73, Phil Barnes-Roberts AD6PQ < Mailto:pbarnrob at acm dot org >
ICBM: 34.2N, -118.1W, Grid DM04we
Opinions=Cash Value $0.02; Not Redeemable for Merchandise.
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