wrote:


"like one case I saw the tuning gang in a Quad FM3 tuner. "


These days I apply it with a syringe right to the contacts.
If the blades are really dusty I use stuff that is completely residue free,
and I DO test it.


** By "contacts" you mean the bronze bearings and fingers that ground the moving plates ?

A few drops of WD40 or similar works like magic and restores normal operation to AM and FM bands.

BTW:

Audio Generators often use a tuning gangs, not just old tube models but also modern examples with FET input sustaining amplifier circuits. The dual gangs used are the same as found in tube AM radios and give the advantages of infinite resolution and indefinite life compared to using a dual pot.

The circuit used is a Wien Bridge and to get down to 20Hz means using 20Mohm resistors in the network ( f = 1/2piRC ). The whole gang has to be isolated from ground since the two sections are connected in series.


..... Phil