Philco Model 80C - tuning question - Printable Version
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+--- Thread: Philco Model 80C - tuning question (/showthread.php?tid=17596)
Philco Model 80C - tuning question - gellenb - 12-02-2017
I have a Philco 80C that I've rebuilt. It was in bad shape when I got it, so it never was pre-tested. I've gone through replacing caps and resistors, coils are good and so on, keeping it the same as what it was without changes. It doesn't exactly match the schematics, and already had the "gimmicks" done. Reception "seems" ok, but I expected better, maybe my expectations are a bit too high. Anyhow, as I go through the alignment all goes well till the last step adjusting the sensitivity. It seems odd that I can't adjust to a point where the squealing starts. Don't get me wrong, I don't want the set to be a "squealer", but for tuning purposes, according to the doc's, it should be adjusted to the point just before the squealing starts.
So for now, I'm just looking to see if anyone has any suggestions before I dig into it again. Are the instructions for tuning correct that it should squeal, and then adjust it back to stop? Any thought are appreciated. Thanks
RE: Philco Model 80C - tuning question - klondike98 - 12-02-2017
WElcome to the Phorum!
The 80 I restored did squeal when the sensitivity hex head nut was turned.
RE: Philco Model 80C - tuning question - Radioroslyn - 12-02-2017
Hi and welcome,
Just a few thoughts. Does your sensitivity adjustment have a fiber nut or a brass one? Should have a fiber one. Check the grid leak resistor for the det circuit, may be high in value. I've found it easier the drill the three rivets out and remove the coil shields as a unit rather than unsoldering the coil and dropping it out the bottom to change it out. You can measure it by checking the resistance from the grid cap to the chassis, the sm caps and coil look like a short by comparison to the 4M resistor.
Double check your resistors around the det to be sure you have the right ones in the right places.
Are you using a signal generator to align the IF stage? If you are trying to do it by ear it's difficult to get it right and it's fairly critical.
You can try making the sensitivity adjustment w/o the ant or signal generator connected. A very strong signal may overload the det.
GL
RE: Philco Model 80C - tuning question - gellenb - 12-03-2017
Thanks for the ideas.
Well question 1 answered, it should squeal when adjusted, so I'll have to go back and check things out again.
The adjustment has a bakelite nut. At the moment, that is still functional, but it has a crack and I have to be gentle with it till I find a replacement.
I ended up replacing almost every resistor and cap including a bad mica which was the first one I ever found bad. Early on I did find resistor (old) that measured acceptable when cold and then once it warmed up opened up. Probably should have just replaced the two or three I kept. That will probably be my first stop.
I had pulled all three coils, which one had the bad mica, resistors replaced. All checked, all good and then soldered them back in. That's wasn't a hard job to do. However, I wonder if when they were soldered back in that created a problem. I've read somewhere here on the web that sometimes the connections get broken when they are resoldered.
I am using a signal generator to align, and by ear, and connected in all but the last step. But your probably right that the generator outputs too strong a signal.
I'll go back and recheck the coils, see what I find there, and re-check and probably replace that last two or so resistors and go from there.
Thanks
RE: Philco Model 80C - tuning question - gellenb - 01-08-2018
It took a while to get back to this radio, but what I found was what I read somewhere. In the beginning, I pulled all three coils and checked them out replacing resistors and a bad mica. Everything was good, they were put back in, and wires re-soldered. The problem ended up being on one coil where the coil wire came off the solder tab, apparently when I soldered the wires back on. So that's what it was, all is good now. Attached a long wire to it, and picked up some stations from half way across the country.
RE: Philco Model 80C - tuning question - klondike98 - 01-08-2018
