Temple G418 oscillator coil problem

[radiotvnut]

A friend asked me to repair his Temple G418 radio. It's one of those el cheapo 4 tube metal cabinet radios. I quickly discovered that the oscillator coil was open. The original coil has a single winding with one tap. There is also a "gimmick" winding. The gimmick winding connects to G1 (pin 5) of the 12SA7. The top terminal on the tapped winding connects to the oscillator section of the tuning capacitor. the tap connects to the cathode (pin 6) of the 12SA7. The bottom terminal of the winding connects to ground.

I ordered a universal oscillator coil from Antique Electronic Supply (P-C70-OSC). This is a tunable coil with a primary and tapped secondary winding that is supposed to work in many configurations. There is no "gimmick" on this coil like there was on the original.

I left the primary winding disconnected, as it's not used in this application. I connected the top terminal of the winding to the tuning cap, the center tap to the cathode of the 12SA7, and the bottom terminal to ground (like the original was). Since there is no "gimmick" on the new coil, I connected a 200 pf silver mica capacitor between the G1 terminal of the 12SA7 and the top terminal of the coil winding (which also connects to the tuning cap).

After tuning the slug on the coil, 1390 comes in very strong. The local stations at 910, 1010, 1290, and 1450 are very weak. They come in fine on other radios. All voltages seem to check OK. I scoped the oscillator circuit and it has a strong signal across the dial. The alignment is about as good as it gets at this point. Tube changing also did no good. Of course, all paper and electrolytic capacitors have been changed.

I'm about to run out of ideas. Does the problem sound like it could be related to the oscillator circuit or does it sound like something else. I don't understand why 1390 comes in loud and clear and the rest are very weak.

Any help is appreciated.

[Reece]

Just a guess but 200pf may be too big. Could the oscillator be overloading the IF circuit? In place of the cap, why not try a gimmick made of two pieces of insulated hookup wire twisted together for 3 or 4 turns. Are you sure the oscillator is right on 455kc (or whatever's right for this set) and that the set isn't aligned on the wrong side of the heterodyne. Believe the LO frequency should be radio station frequency plus 455, not minus 455.
Good luck,
Reece