[Collins] 32S-3 mic gain pot needed

[Dr. Gerald N. Johnson]

That's a pot unique to the 32S-3 and 32S-3A. Most stock dual pots have 
the same resistance in both sections and the common switch is open at 
full CCW, closing as one rotates clockwise. Now it used to be that TV 
parts stores had kits of parts to assemble special pots, but even then 
the switches often didn't have any option other than the radio 
volume/power switch combination. In designing the diagnostic panel for 
the 821A-1 I wanted a pot with a switch that closed at full clockwise 
for the RF drive control. I went to a small TV repair shop in Central 
City where I lived on a Saturday and bought the pieces and at home I cut 
off the switch mounting tabs and soldered the switch in the position to 
give the switching action I wanted and used that to build the first 
diagnostic panel. I don't remember how I got Collins to pay for those 
parts. Then when the design was accepted I had to get a component 
specification so the parts could be bought for production. Probably 
bought no more than 20 of those pots for all the units made.

While the resistance element has continuity end to end its probably worn 
away where the wiper ran, so disassembling the pot and bending the wiper 
won't help. A cobble could be to connect a 100K or 220K resistor from 
the hot terminal to the wiper. That will move the operating range to 
where the wiper makes contact. It will make adjustment touchy. 
Alternatively the resistor could go from wiper to ground. Either way 
makes the contact part of the pot position give an output like it did 
when the wiper made contact. Another alternative is to depend on the low 
resistance section of the pot for transmitter gain control and unhook 
the 500K section replacing it with a pair of resistors totaling about 
500K and giving the ratio needed for decent transmitter audio and a 
modicum of ALC action. These aren't elegant solutions to the bad pot, 
but are workable at low cost.

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association.

On 12/22/2014 9:15 AM, Al Parker wrote:
> Hi Folks,
> Does anyone by any chance have a dual pot, with switch, that would do
> the job for a mic gain pot in a 32S-3? One secn is .5meg, the other is
> 2500 ohms. Or do you know where one might be found? The .5meg section
> has about 90 degrees of rotation where the slider doesn't make contact
> with the resistor. The resistance is continuous, but the slider contact
> isn't. DeOxit Blue doesn't help.
> I remember there was a thread on one forum recently where a parts
> supplier had many dual pots, but of course, I didn't keep the reference.
> This is for a friend of mine's xmtr. I had posted a question re: the VOX
> ckt about a wk ago, and got good answers which solved that problem. I
> got the replacement resistor for that on Sat., put it in, and did a
> final ck out on the rig. No audio from the mic from about 10 o'clock to
> 2 on the ctrl.
> If I could get pieces/parts, I might be able to assemble a working pot.
> Any help would be greatly appreciated.
> thanks & 73,
>
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>