AR 2a Restoration: Pots & Midrange Cones

[Martin]

I have a beautiful pair of AR 2a that look like they just came out of their original boxes. They are all original, as far as I know. There are 2 problems with each speaker which I'd like to fix so that the speakers become (nearly) perfect: 1) Tweeter output is very soft, which I assume is due to dirty pots, and 2) There are a few tiny, 1/4" tears in the delicate midrange cones which I'd like to repair even though the tears are not audible.

Inside, I expected to see the common, black & white Aetna-Pollak pots, but these are very different: they're much larger in diameter, they appear to be all-metal, they're perfectly quiet and rotate with a feel as smooth as silk, making me wonder if they're dirty at all. They're labled "Violet B150 AT4011", and appear to be original, although I've never seen this different type of pot before. Rotating them does not alter tweeter output level at all, making me think they're dirty, but they sure feel smooth and not dirty or corroded. They are not as easily removed as the A-P pots, in fact, it is not obvious at all how to remove them as they are firmly seated even with the rear, outside nut removed. They seem to be glued in place, though no glue is obvious. The midrange pots work fine and are perfectly quiet.

Are these pots likely to be the culprit given that they are different from the A-Ps and appear to be of much higher quality? If so, what's the best way to remove them?

Then, I'd like to use some kind of flexible coating on the midrange paper to seal the little tears from the outside. Would the red Permatex gasket compound work? Getting to the inside, behind the cones, is a bit of a problem due to both a) very short midrange wires and lots of fiberglass stuffing inside the midranges so patching the cones from the rear is not too likely.

Your comments & suggestions are appreciated.

[RoyC]

Martin,

AB Tech sold "Violet" replacement controls in the 90's. They look like the typical 8 ohm l-pads everyone is selling now (including AB Tech) but were actual 16 ohm potentiometers. They did work very smoothly, but (like modern l-pads) cannot be opened for cleaning.

Your tweeter problem could be the controls, the control connections, or deteriorated tweeters. I have been seeing many phenolic dome tweeters (and phenolic dome AR-3 mids) with erratic output lately.

Permatex gasket sealant would not be the best choice for the mid cone tears. It would be better to use a good white glue and a small piece of tissue paper. Don't use too much paper or glue.

Roy

[Martin]

Thanks, Roy. Those Violet pots have such a nice feel to them. Perhaps I'll bypass them to see if I get greater tweeter output.