[ARC5] Carbon Comp Drift

[Glen Zook]

The 6-cathode resistors in the Heath SB-Line and in the Collins 32S- series transmitters and the KWM-2- series transceivers, that serve as the "plate" current (actually cathode current) meter shunt, go high all the time.  I automatically replace those resistors with modern 1-watt, 5% tolerance, resistors which are now pretty close to the same size as the original resistors.


Those resistors are 10-ohm and 12-ohm in value and always go high in value.  This then throws off the meter calibration so that the meter reads a higher value than what is really being drawn by the final amplifier tubes.

 Glen, K9STH 
Website: http://k9sth.net

      From: Richard Knoppow <1oldlens1 at ix.netcom.com>
 To: arc5 at mailman.qth.net 
 Sent: Saturday, March 2, 2019 3:38 PM
 Subject: Re: [ARC5] Carbon Comp Drift
   
    This is pretty much the pattern I've found, the higher the 
original value the more they drift but I've also found low value 
resistors that have drifted a lot. For instance the 15 ohm 
cathode resistors in some Drake transmitters. Some, appeared to 
be Ohmite, were close but others were up to 20 or 25 ohms. These 
had longitudinal mold marks on them, I have no idea of the brand. 
In the Drakes the resistors are part of the circuit that measures 
plate current, its important they they are close to the right 
value. There are other CC resistors in this circuit and are 
frequently off value. In my AR-88 resistors below about 50K were 
close enough to leave alone but higher values were way off. I 
have no idea of who made them.

   
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