The PHILCO Phorum

I found this radio on Ebay.  It is the same model my mother listened to every day while working in the kitchen.  I fell asleep to it listening to WLS in my early teens.  Certainly not a great radio but I have it working for nostalgia reasons.

Question for the experts among us on IF transformers with silver mica disease:  I cut out the silver mica caps and installed new mica caps and the radio works.  I was able to tune the transformers for the 455khz IF.  However, I did not have the exact caps.  Instead of 110 mmf, I used 100mmf, and on the second IF, instead of the 75 mmf, I used 70 mmf.  As I said, I was able to peak the IF at 455.  The question is, does the efficiency of the IF transformer suffer by reducing the capacitance of the LC circuit and increasing the inductance?  The radio works ok, but is not as sensitive as I think it should be.  (I have to say, though, I did not test the tubes., and I have no experience with AA5's.)

Just as an aside, I was pleased to see that this design isolated the chassis from line voltage.

Back in the day caps could be plus minus 20% ecaps plus minus 50%.

Could you tack in some small values, or even add "Gimmicks" outside the cans to test whether it makes a difference? Just a thought.

I suppose the real question is whether the change affects the coupling in each transformer by a significant amount. Also not to be forgotten is that the transformer resonance is also affected by the type of circuit and wiring layout, so the real value of capacitances across each coil are never exactly the book value. 5 - 10 pf is pretty easy to gain or loose.

Cheers

Ed

Thanks guys. I was indeed thinking of tacking a few 5mmf caps across the pins of the IF to see if it made any difference. thought I'd ask before I went through the trouble.