RCA 141 oscillator coil trouble Mar 23, 2021 20:11:48 GMT 12
Post by DHockey on Mar 23, 2021 20:11:48 GMT 12
For the past few months I’ve been working on the restoration of a RCA 141 which is the export version of the RCA 140 / GE K80. Its quite an interesting radio but very difficult to work on. Lots of rubber covered wire to replace along with a coil sub-assembly that needs removing to get access to many components. Probably the worst of the early 30’s RCA “deep chassis” sets. This isn’t to say that I haven’t enjoyed working on it, I like a challenge! The radio came from the estate of Ross Paton in “basket case” condition, partially dismantled but with rewound power transformer, field coil and choke.
Here are some photos:
The valve line up is:
58 1st RF amp (used on band 4 only)
58 RF amp
58 IF amp
2B7 Detector and 1st audio
56 Audio driver
53 Class B output
I’ve run into a problem with the broadcast oscillator coil in the radio. When I initially checked out the coils with my DMM everything was OK, continuity and no shorts between windings. However when I was doing an alignment on the set I noticed that there was voltage present on the oscillator section of the tuning gang (about 160V) when the radio was switched to the BC band. This voltage was not present when the radio was on the shortwave bands. A leakage test revealed that there was about 2 Megs of leakage between the BC osc. coil primary and secondary which would drop to about 700K when the coil was warmed with a hair dryer. The radio does work, but I’m concerned about the insulation between the two windings breaking down further and causing more trouble. Also I don’t want high voltages floating around on the top of the chassis.
I’m wondering what I can do about this, swapping out the osc. coil would be the answer in most other sets, but this RCA is a bit different. The IF is 445kHz rather than 455kHz and the tuning gang capacity is 335pF (full mesh) which is a bit lower than a lot of later radios so I’m thinking that a coil salvaged from my parts stash may not work well if at all?
Any suggestions would be much appreciated, its taken a lot of work to get the set to this stage and its a bit of a bugger to run into a potential show-stopper when the radio is almost finished!