Philco 90 Stoped Working - Printable Version
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Philco 90 Stoped Working - Steve Davis - 03-26-2020
Some may recall, I restored this late version 90 (2 PP 47 output) last winter. It started about a month ago, the radio would stop playing. You could tune to the high end of the dial and it would come back on. It may work for several days before it would happen again. It began to get more and more frequent, finally getting to the point it would never play on the low end. Suspecting the oscillator, I confirmed using another radio. First I tried a couple of different 24A tubes in the oscillator position, one gave a slight improvement but, would still drop out. Tonight I pulled the chassis out and used a heat gun to heat the oscillator coil while it was still installed in the chassis. The radio now plays fine. I plan to use the radio as long as it keeps working. If it happens again, I'm thinking about doing Ron's "super" mod. The late version 90 is pretty much the same as the 91 except it has 2.5 volt tubes so, I would have to use a 2A7 tube for the oscillator. Any thoughts?
Steve
RE: Philco 90 Stoped Working - morzh - 03-27-2020
Steve
Personally, I am of a conviction that if a radio is supposed to play and was design to do so and is known to work, it then should work. If it doesn't it then can be fixed without any mods.
Unless you just want to do a/the mod.
RE: Philco 90 Stoped Working - Ron Ramirez - 03-27-2020
Steve
To a degree, I have to agree with Mike.
Have you rewound the oscillator coil? If not, I would try baking the coil for 30 minutes at no more than 200 degrees Fahrenheit. That should remove moisture from the coil form and the radio should perform better as a result.
If the problem persists after baking the coil, then you could consider a 2A7 mod.
The autodyne circuit was a poor design to begin with, and it would bite Philco in the behind, especially with troubles with the 19 and 89 later on.
RE: Philco 90 Stoped Working - John Bartley - 03-27-2020
Just some thoughts ...
Steve heated the coil with a heat gun and normal operation came back. So if the coil comes out, gets baked to remove the moisture, would it then be prudent to dip it in melted paraffin and drip dry to get rid of excess paraffin as soon as it comes out of the oven? The paraffin should seal it against moisture absorption for a long time?
RE: Philco 90 Stoped Working - Steve Davis - 03-27-2020
As long as it keeps working, I'm not going to do anything. I'm just thinking ahead because, at some point, it will probably quit again. John is right, bake the coil, bake it and immediately seal it, it will probably last many years. But then, I like a challenge . I did this mod on a Philco 19 two or three years ago and it worked very well but it was one of the tough ones that wouldn't respond to any of the normal tricks.
Steve