[AMRadio] AMRadio Digest, Vol 124, Issue 2


Donald Chester k4kyv at charter.net
Sat May 3 11:11:42 EDT 2014


I'm not familiar with those. Some of the old gear I work on uses resistors
with the body/end/dot coding system. The wire leads are  wound round the
carbon comp body of the resistor at the tip ends and soldered, and come off
the resistor body radially. I have found that in many cases, the resistance
value has drifted far away from nominal. The same goes for regular axial
style carbon comp resistors in older equipment.

In earlier equipment, like my 1935 HRO, they used resistors with moulded
solder end caps and radial leads. They resemble RF chokes made the same way,
except for the white ceramic body with no wire on it. The body is hollow and
the resistance material is inside.  With those, the values are usually
stamped on the body with actual numbers.

When restoring older equipment if I  want to preserve the original style
resistor, I usually check the  resistance with an ohmmeter and use a
resistor that actually measures close to the desired value, regardless of
what the color code says it's supposed to be. If the resistor is off-value
to the extreme, I won't use it, but if it has drifted plus/minus 100% or so,
it's probably OK. In that  case, it  might be a good idea to re-paint the
code to correspond with the actual resistance. 

Wonder if anyone has ever observed whether the resistive value of a carbon
comp resistor that has drifted with age is as stable as it originally  was
when new.  One possibility is that as the value drifts, it tends towards a
final, more stable value albeit different from original, in which case it
would be OK to use. The other possibility is than once the value starts
drifting, it has become unstable and would no longer be reliable enough to
use in a circuit. Since resistor value drift is a long-term phenomenon that
might be a matter of years or even decades,  I have  never run an experiment
or otherwise had the occasion to observe it.

This could be useful  when looking for a certain value of resistor, and the
only  thing you can find in the junkbox  that even measures close is a
drifted value.



-----Original Message-----

From: "David Knepper" <collinsradio at comcast.net>
Subject: Re: [AMRadio] FT243 crystal sockets, half-watt resistors


Don, I am looking for any value of resistors that had a cap on each end and 
the values were painted on as a stripe.  Use in pre-WWII radios.

Do you or anyone else have any?

Want to complete my Collins 30W transmitter made back in the 30's

Thanks



David Knepper - W3CRA/W3ST


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