Hi all, nearly a year ago I was restoring this am/fm table top Philco radio given to me by a friend. Had it all done except I needed a speaker which I could never find. The real problem is it has SMD so with that I put it aside until now. I was able to find another exact model radio. I decided to restore this one too. It also has SMD so now I have a question. First of all, I know there is a difference between the 1st IF transformer and the 2nd, impedance wise. Input and out put transformers if you will. However, I have 2 no name AA5 radios for parts and both of them have the same part #s in their cans leading me to believe both transformers are identical, primaries and secondaries both ohm out the same between them. I hate to look for another Philco set of xformers as I feel they are prone to SMD. I would transplant the xformers from the parts sets to the Philco but for one caveat. The first AM IF transformer has 3 separate coils, a primary, secondary and some third coil not totally connected electrically, a design I’ve never seen before. Part # 32-4516A!
Just wondering if a regular 455kc input transformer would still work and what exactly does that middle coil do?
Ron
Hi Ron,
That tertiary winding is used to inductively couple the 455kc signal to the two slug tuned coils. This adds a bit of selectivity to the circuit. Can you use a transformer w/o it?? Sure. Just wire it like all the other IF transformers. Top of the pri to the plate of the mixer, bottom of the pri B+, top of sec control grid of 1st IF amp, bottom to avc line.
Besides how else are you going to use all of these spares you have save up over the years?
I ran into this problem a while back. When I opened the cans the caps were connected in with brass spring loaded fingers. I lifted the fingers, put everything back together, soldered 56pf caps on the external terminals and no more SMD.
Thanks Terry, I figured it was some sort of tertiary thing going on especially since only one end is connected to anything. It just baffled me as to why make it that complicated when every other AM radio I’ve seen only has a primary and secondary! My only question now is why do the parts sets I have, different brands, have the same part # on input and output IFs. I would think they should be different!
Rod I tried to rebuild or bypass the caps in the first Philco but they are molded into the plastic base and I ended up boogering them up!
Ron
If it's a good physical match grab the input transformer and install it.
Ron, on to plan B. I kind of figured they would be different, guess I got lucky.
Just curious, does anybody know of anyone making ‘universal’ replacement IFs? I can’t find anything being produced by the old standards in the coil business like JW Miller, Merit, Meissner, Triad…etc.
Ron
Hello Ron,
I will see if I can find anything I have seen the small mini ones sold on alliexpress .
Sincerely Richard
Thanks Rich. I’ve seen the minis too for solid state sets and PC boards. I’m looking for the 3/4” K-Tran type used in tube sets.
Ron
Quote:Thanks Rich. I’ve seen the minis too for solid state sets and PC boards. I’m looking for the 3/4” K-Tran type used in tube sets.
Ron
Ron,
Do you have a particular model numbers you are looking for, Miller, K-Tran, etc, use a cross reference found in Sam's for these?
What do you expect these transformers to be worth to you new?
Used good coils, w/SMD?
I have stock of a half dozen closed shops and a distributor local to me. I am of the inclination, that if one of my "Shelf Queens" decides to come out of retirement and has SMD, unless significant to me, like a "family heirloom" I will part company before I do IF surgery. Therefore my inventory is excess..
Please post any additional significant data...
Chas
Hi Chas, I believe both AM IFs have SMD. The 1st IF or input IF is Philco part# 32-4516A. It’s the one with the extra winding in my original post. Being of unique design, I don’t see an after market replacement. The 2nd or output IF is Philco part# 32-4517A which I found in a Thordarson cross reference to be #16-6758. Both of these transformers are of the Ktran variety that use a ‘U’ clip from the bottom to mount on the chassis. Thanks
Ron