March 4, 2021 at 5:46 am #16354
I’ve just started the restoration of this Phonola and it appears as if I have open primary windings on the oscillator coil. Both windings appear to be open which seems odd to me but I’m a rookie so maybe that’s normal?? The only number I can find is P170 which is stamped on the can but i don’t think that’s an actual part number for the coil. I opened up the can and there’s no part number on the coil either. Is this a common coil that I can find a substitute for? Any other suggestions? I’m attaching the schematic.
Attachments:March 4, 2021 at 6:19 am #16356
It’s very unlikely that either coil is open circuit, so both being open is almost unbelievable! What test points did you use? You might have included S3 in the test, and that could be where the fault lies.March 4, 2021 at 6:58 am #16357
That’s what I suspected as well so I traced the connections from S3 to the coils (and from R3) and checked the coils directly. The antenna coil is similar so I had a reference in terms of where to check and those coils check out fine.
ThanksMarch 4, 2021 at 7:47 am #16358
OK, so even if the G2 connection on the 6A7 is shorted to ground somehow, the 217V at point B can only produce 11mA through the primaries. I doubt if that would burn them out.
Maybe the junction between R3 and C6 is dry?March 4, 2021 at 8:35 am #16359
Good point….I’ll check that outMarch 4, 2021 at 2:51 pm #16366
No joy. The connections are fine. I took measurements right at the coil itself this time just to eliminate a chance of a broken wire or cold solder connection. There is no continuity between ANY of the tabs on the coil. I’m adding some pics. Does this look like a healthy coil?
Attachments:March 4, 2021 at 3:38 pm #16369
It’s possible that the connection of the winding wire itseslf to the tab has gone AWOL. I’d be tempted to apply fresh solder and a hot iron to every tab where the connections are made. Easy to do, confirms good connections. If that doesn’t solve it, then you obviously have bad winding continuity and some deconstruction would be the next step.March 4, 2021 at 7:25 pm #16370
A good suggestion but that didn’t help. I can’t begin to think about how to deconstruct this coil as it’s covered in wax that has deteriorated. I can’t even see the secondary windings as I’m not familiar with how they should appear on this coil. Are they under the wax or ??
I’m thinking that a replacement is in order. Given that this is a tuneable coil, is there a “generic” replacement that I could source? Does anyone know where I might find one?
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