[R-390] RF GAIN pot ?

[David Wise]

Reverse Log is the usual taper for a gain control that is wired as a cathode resistor.  The taper cancels the tubes' bias-vs-gain curve, leaving you with a linear control action.
It's reverse rather than forward because minimum resistance is maximum gain.  You want resistance that changes rapidly at first, then slower and slower as it approaches zero - ideally, a constant percentage change per degree of rotation.

Any volume control that is wired as a voltage divider in the audio signal path should be audio taper.  The taper cancels the human ear's logarithmic SPL-vs-perceived-loudness curve, leaving you with a linear control action.
You want a divider ratio that increases slowly at first, then more and more rapidly as the ear compresses.

Dave Wise

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Craig
Sent: Friday, March 18, 2016 8:14 AM
To: 'Jacques Fortin'; r-390 at mailman.qth.net
Subject: Re: [R-390] RF GAIN pot ?

Jacques,

No, not crazy............but I'll add more confusion. Those numbers on the
back of CTS pots might only have meaning to CTS. Haven't been able to find
squat. The RF gain pot in my junk box has on the back......SM-C-283204-2
5K CTS8524............go figure? 

But according to the web and how to measure a pot; it is 5K ohms reverse log
taper. 

Still learning,
Craig