My father picked up a 37-690 that has been restored just recently. The only major problem is band 2 does not work. My father talked to the guy that rebuilt it and he claims most if not all 37-690's have bad oscillator coils causing band 2 to to be inoperative. He also claims replacements are not available and repairing the existing coil is not an option. Does this sound correct? My father has a spare 37-690 for parts, possible good oscillator coil? He also has 3 37-116's do they use the same oscillator coils?
I also don't think this guy spent much time aligning the radio either as it tunes kind of funny almost like anti AFC. This is with magnetic tuning off.
Looks like aligning one of these beasts will be a pain in the neck.
If the oscillator coil is at fault and a replacement is available it looks like fun. My father was a radio repair man in the mid to late 40's then worked as a radio engineer at a local AM/FM station for 45 years. Trouble is he is 84 years old so it looks like I'm going to be the man for the job.
Thanks for your time
I had a 37-675 with a bad band 2 oscillator coil. I ended up pulling the coil out and rewinding it. I'm sure it is possible to rewind the coil on a 37-690, it just isn't very fun. From the schematic, the 37-675 and 37-690 use the same band 2 oscillator coil. IIRC, the 37-675 also used the same sub-chassis as the 37-116. I'll try to remember to look to see if I have notes from when I rewound that coil.
The guy that did the rebuild claims he has attempted to rewind band 2 oscillator coils without success. I hope he is wrong and a rewind and or finding a good used one is possible. I would research what radio's use the same oscillator coils myself as my father has a complete set of rider manuals. Trouble is he is such a pack rat I would need dynamite to get to them.
No need to dig out the Riders, most schematics are here:
http://www.nostalgiaair.org/Resources/
A quick check of the parts lists for the 37-690 and 37-116 show that some of the coils (transformers) are the same.
Models 37-116, 37-675 and 37-690 all use the same RF subchassis; thus, they all use the same coils.
The coils can be rewound, but they are very finicky. If the wire size is not exactly the same, and if you do not dry out the coil form first before proceeding, the rewound coil will not work. Older Philco coils are much more forgiving.
Like Ron says, if you rewind you will have problems.
Getting the proper inductance is not the problem- that's relatively simple. The problem comes about in something called distributed capacitance- that's the capacitance between the turns and it can be substantial.
With a rewound coil you will be able to set the bottom of the dial and adjust the trimmer for the high end but the middle will be terrible.
If you can remove the oscillator coil for band 2, and you have a good magnifying glass or stereo scope, look for a wire break on the outside layer of the coil; carefully follow the wire back from it's solder connection. The wires nearly always break where the person winding the coil made a 90 degree bend at the end of the coil as it runs to the solder joint. It's going to be under a tape or paper covering usually. If you find the break you will be able to remove one or two turns without any problems.
From the old coil winding department of Boonton Radio-
Thanks everyone for the info. Looks like its time to check out the other chassis. wish me luck!