My first run-in with "the disease"
My collecting interests are pre-silver mica, so this is the last silver mica era set that I will fix for a friend.

I have low gain in IF stage and a +2v grid on the IF tube. Everything in a 5 mile radius has been checked or changed. It all is pointing to "the disease".

Just thinking someone here has done a TO and knows what values the caps should be. I would think that these 455 khz transformers are pretty much the same in these battery sets. I am trying to avoid making this more of a project than it already has been. It would be easier to tell you what has not been wrong with this set so far.

Anyone want to fix these 2 transformers for me? I'll be your best friend...

They are probably not the same values as in the Zeniths, because the IF transformers are of a totally different construction.

Most of the 3/4" source 119 (Automatic) IF transformers like the one pictured have caps in the 100-110-120pf range, but not all are the same and cap values all over the place have been reported.

Best bet if you are unsure is to remove the original mica sheet, bend/clip the contact pads so they don't short out, put it back together and in the radio, and install the new caps externally directly on the solder terminals.

If you have a way of measuring inductance it is easy to calculate the correct value of the caps. You will know you are close if it doesn't take more than about 1/2 turn to 1 turn on both slugs to align it.

So, I can remove the mica and completely leave it out? I thought I recalled someone putting paper between the mica..

Can I use ceramic disc capacitors on the bottom?

Thanks.

You can leave the mica out as long as you modify the contact pads so they don't touch. Many people just clip them off. Otherwise if you leave them there, you have to provide insulation so they do not touch. Paper isn't a good choice since it could absorb moisture from the air. Plastic could melt from the heat of soldering connections to the terminal lugs.

Disc ceramics can be used provided they are NP0 temperature coefficient, but silver mica caps are preferable, readily available and not expensive.

I used 100 pf for each winding and I was able to peak both transformers nicely at 455 khz. I think one I had to turn the slug about 1-1/2 turns, but it peaked. Radio is playing very nice now.

Just curious Scott, what did your 100 pf caps actually read.
Bill j.