[HarryWeatherford]

That advice really helped. I ordered some of that paper. For now, the AM and SW work great. I am now battling one issue and I think it is related to the previous person's mods they made. They had tried to open the secondary of Z301 (from ground) and inject the signal bypassing Z300 and the primary of Z301. I have the FM now working even though it is very low in magnitude and a big loss of signal at the low end. I did find a loose solder connection on L401C, maybe there are more issues in those tuned circuits. The one issue that I face now: I can tune Z301 to peak off line by signal injecting but..... when I apply power the voltage on C314 drives really hard (in the order of -50 vdc). There may be self oscillations happening (?). When I do tune this transformer off-line, then I knock out my AM, so then I adjust Z301 for AM - works great but now it's like a dog chasing his tail. So I basically can't do a full FM Alignment because of this C314 voltage issue - I've convinced myself that these tuned circuits are the reason the FM is not working correctly. Maybe I need to pull out the can again and check for shorts (?). I think this was the problem the last guy faced. Maybe I'll step back and completely go through the FM checks - it seems like on 7F8, from the FM checks, I should read a negative voltage ( I think it was pins 1 to 4). I'm really hoping that is not the problem area because it's pretty tight in that area with the band switch and socket right below it. I ordered a set of fly-legs just so I could reach under the band-switch to take measurements. This unit was going to be a gift to my son so I am not ready to throw in the towel. Any advice or suggestions from the experts would really be appreciated.

[HarryWeatherford]

Dale H. Cook: I visited your website - really nice! There's a wealth of information there - thank you for sharing

[HarryWeatherford]

I went back to the tuned transformer and looked at those again.  After removing the guts from the can,  I put my meter directly over the variable capacitor(s) and found that at one point - the plates of the cap are basically shorted together.  That matched with both capacitance and resistance measurements across the variable cap.  I'm sure these are small metal plates that move closer together, separated by thin layers of mica for the dielectric.  Now I know why during alignments, when I dial the caps to a certain spot, the voltage across C314 does through the roof.  So my question is:  Is there any way to repair or fix these small adjustable capacitors?  Could the small adjustment screw be touching both plates shorting them out - should there be insulating paint on some of the screw threads?

[RodB]

Hi Harry,

The mica sheet in the adjustable capacitor we often find after 80+ years gets dirty, the dirt collects moisture and causes all sorts of problems. It is removable and can be cleaned. Just remove the adjustment screw and the mica should be loose and can be coaxed out of the metallic sandwich. Be very gentle, they are delicate. Occasionally you will find one that has a crease someone else has damaged during removal. Place the mica on a flat, clean surface and soak it with alcohol, then gently wipe it clean. Use a brush soaked with alcohol to clean the capacitor, then put it back together. One of the plates is spring loaded so don't be too aggressive on the cleaning.

[HarryWeatherford]

I've been reworking these transformer cans - bad fixed cap - - solder blob shorting a cap out - adjustable caps needed cleaning - missing fish paper for insulation from the cans. Great advice RobB ! I did make a really rookie mistake/comment - I'm use to working with very large ac and dc motors (and drives) so winding resistance is really low. I couldn't understand why the schematics listed winding resistance... then I opened that first can and I saw how small the winding wires were. To make a long story short - "someone" had my Fluke meter set to ohms when they tested for high dc voltage. Bad bad bad! All resistance measurements were useless - a new meter finally showed that R405, a 22 ohm resistor was actually about 22 ohms - not 0.3 ohms! That bad meter reading had me chasing my tail.