1950 vintage Motorola IF transformers?

[nasadowsk]

Ok, for those who haven't seen the 'Beautiful Motorola!' thread on the B&W TV forum, well, that set came with an AM/FM radio. Right now, I'm attacking the radio, and I've found that I've got a nasty (nasty!) amount of noise on the AM band (and less so on FM). I've traced this down to a leaky IF transformer - it's one of those round can types where you press and turn the ceramic base to pull it out (neat! This consoles full of neat features). There's a leakage from the input to the output side, which seems to be via the capacitors formed into the base of the coil. Anyone ever have this on a Motorola before? I'm trying to figure to a way of dealing with it - if cleaning the thing will help or not. It's a REALLY weird design, I've never seen it before.

[nasadowsk]

Well, pulling out the silver/mica capacitor thingie did the trick. The ski-matic shows that the AM cans are 100mfd capped and the FMs are 33mfd, so I'll just get standard ceramics and solder them in.

I guess this was a way Motorola was going to cut costs and keep quality, but it didn't pan out over 50 years, though let's be honest - the thing wasn't expected to last that long. It's a neat design that looks like it could have been easily automated, and the cans themselves are pretty darn solid. Except for those darn caps. Oh well.

[Chad Hauris]

I just worked on a 1952 motorola AM radio and had to drill out the bottoms of the IF cans to remove the offending mica sheets and then bend back the contacts so they would not short. One of the things came apart and I had to heat the coil, remove it and resolder the wires! I did use 100 pf ceramic and it works well. Just soldered the caps in on the bottom of the chassis at the transformer terminals.
Some of these old cans it is easier to remove the mica sheets than others.

[nasadowsk]

The cans on this thing are easy and fun: remove all the component leads, then press and twist, they pop up and come right out. I then clipped and pulled the sheet out and blew out any mica shavings left. The clips are a bit of an issue - I might superglue them to hold 'em in place so they don't short. I can fit new caps inside the cans, so it'll look origional. Sucks the design didn't hold up with time - it's pretty neat.

I have to attack a front end issue, but the noise was so dominant that I couldn't get %^%^$& done for diagnosis - you couldn't see a nice trace on the scope.

[gadget73]

Lots of radios from the 50s through the end of the tube era had those type of cans with the mica and silver contacts. Luckily the old dinosaur Philco doesn't have them and my Euro rigs don't either. They've got funky dogbone ceramic caps in there though.

[Tony V]

Originally Posted by nasadowsk

The cans on this thing are easy and fun: remove all the component leads, then press and twist, they pop up and come right out. I then clipped and pulled the sheet out and blew out any mica shavings left. The clips are a bit of an issue - I might superglue them to hold 'em in place so they don't short. I can fit new caps inside the cans, so it'll look origional. Sucks the design didn't hold up with time - it's pretty neat.

I have to attack a front end issue, but the noise was so dominant that I couldn't get %^%^$& done for diagnosis - you couldn't see a nice trace on the scope.

Dont use super glue to hold the clips as you might run the risk of damaging the coils wires from the outgassing of the glue. The wires corrode easily in these transformers. Use something like hot glue to do the job so you wont have problems later.
-Tony

[nasadowsk]

Well, the radio's alive

I got the AM band working, and the first thing that came up was WABC, right during their Saturday night oldies show! That just added to the cool of getting the thing going. The antenna needs work and the FM's still dead and oh man will it need an alignment, but it's getting there

[wa2ise]

That's the IF K-tran disease. See my page (about half way down) http://www.geocities.com/wa2ise/radios/repair.htm