Admiral 24A12x tuner part

[Tony F]

While going through an Admiral 24A12x set I was cleaning up and re-lubing the tuner. I noticed that the "fine tuning" wiper had a gap of about 1/8" so that there is no contact, thus no fine tuning. Looking at another tuner, it looks like there is a highly polished metal disc that is either bonded or soldered onto the exposed metal piece shown in the pictures. The one that was in here is long gone. Has anyone come across this before ? Was it soldered on ? or do I need to obtain an entire piece from another tuner. Looks like I'd have to drill out the 2 rivets and replace the fine tuning "button" assembly in order to make contact with the "wiper" again. The square aluminum metal retainer has been removed in the pictures so that I could get a picture of the "disc" wiper area.
Thanks, Tony

[Notimetolooz]

I think the disc and rotor form a variable cap that effects the tuner local oscillator. Nothing is missing in that case. If the fine tuning is working why fix it?

[Tony F]

Thanks for the explanation, makes sense. I haven't powered this set up as I am still working on it. I have 3 of these sets and this is the only one that seems to have more "play" in the fine tuning shaft. I am almost thinking that someone has had it apart in the past, and was not put back together with the small parts, (springs and washers) correctly. Also, the "button" area seems to be quite a bit rougher than the other ones. i just wanted to clarify.

[Tom9589]

The square aluminum metal retainer you mentioned is one electrode of the fine tuning capacitor. The round disk mounted in the tuner body is the other electrode. The phenolic disk is the dielectric. By turning fine tuning shaft you vary the amount of dielectric between the electrodes. According to Admiral, the fine tuning control varies between 3 and 5 pF. You will have to install the square aluminum metal retainer for the fine tuning to work.