"Michael Black" wrote in message
ple.net...
On Sat, 18 Dec 2010, Mahoidar wrote:

I am looking for parts to build a portable tube transmitter-receiver
project from an artcle that appeared in the September 1950's QST.
It utilises a dual potentiometer, one gang is 2M ohm, the other is 5K
ohms.
The parts list gives the 2M as "RC M13-139" and the 5K as "IRC PQ
11-114".
Do these numbers mean anything to anyone, and if so, please can you
explain?
Any assistance will be greatly appreciated.

But what are the pots doing? Is this a space saving thing, or is there
some concrete reason why the pots are ganged? Even if they "need" to be
ganged, the circuit will define why, and we don't know what the circuit
is.

Michael VE2BVW


The pots are ganged because one controls the audio gain and the other
controls bias on the grid of the convertor tube. The circuit in question is
"The Mountaineer" - A Hiker's Portable,
featured in QST for September 1950.
I suppose two seperate pots could be used, but a dual pot makes life easier.