Have some odd variations from schematic

[Schanz]

I picked up an airline 94BR-1535a and have recapped it. I also replaced missing tubes. AM works fine but FM is just static. I started digging deeper and noticed a couple of irregularities. T7 has a small cap bridging one side and what looks like a dog bone resistor bridging the other side. Can't find this on the diagram. Anyway, the resistor tests open. Was this some repair or factory adjustment? Also, from T9, there's a 3.3m resistor where c22 is supposed to be. Did someone mistake a color coded cap for a resistor? I've reinstated c22 and AM seems to work better. I've also ordered new FM tube 6au6 for kicks.

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[tom.j.fla]

What you are describing for T-7 is silver mica creep. What looks like a dog bone resistor, is a ceramic cap. more than likely you have at least one more transformer with silver creep. If you have a signal generator try to feed a 10.7 megacycle signal through. Using a signal tracer try to follow the signal till you lose it, then start testing parts in that stage. All the best, Tom

[tom.j.fla]

How about posting a pix of the under chassis area of the transformer in question? All the best, Tom

[Schanz]

Ok, It was actually T5, not T7 bit the same applies. The brown cap on the left was removed while I tested it and was replaced with longer leads due to the tight space. The ceramic "dog bone" is on the left.


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[Captainclock]

Originally Posted by Schanz

Ok, It was actually T5, not T7 bit the same applies. The brown cap on the left was removed while I tested it and was replaced with longer leads due to the tight space. The ceramic "dog bone" is on the left.


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Are you referring to the round green thing with the oddly painted stripes on the top? If so, that's not a resistor, that's an early ceramic capacitor (not a ceramic disc capacitor, but a ceramic capacitor, although they work much in the same way as a ceramic disc capacitor does.) So with that in mind, you do still have a capacitor in there, it just doesn't look like what you were expecting it to, and from the looks of it, it might still be the orginal ceramic capacitor yet, because that style of ceramic capacitor was more common in the late 1940s, and early 1950s which is roughly when your radio was made. as for the "ceramic" tubular capacitor looking thing, that's a variation on the mica capacitor, rarely do they go bad, unless you have silver mica disease in your IF Transformers but even then that was mostly more common in the smaller IF Transformers that were installed in radios from the mid 1950s up until the early 1960s when they finally went over to solid state radios.

[Electronic M]

Originally Posted by Schanz

Ok, It was actually T5, not T7 bit the same applies. The brown cap on the left was removed while I tested it and was replaced with longer leads due to the tight space. The ceramic "dog bone" is on the left.

Nix those lead extensions! They will add capacitance and change the tuning of the stage that cap is in. In FM and TV especially lead dress is CRITICAL....Everything (except paper caps) should be undisturbed or tested/replaced maintaining as close to the original lead dress as possible....Otherwise alignment may be needed, and in the worst case alignment won't be enough to fix lead dress discrepancies.

[Schanz]

Thanks. I'll leave it be. Going to wait on a new tube before doing much else. Been tracing the schematic tonight just to verify everything is where it's supposed to be.

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[Schanz]

True. I actually knew that but didn't think to apply it.

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[Schanz]

I put this radio aside for a while but went back to it today. Discovered totally by accident that if I leave the 6AL5 fm detector out, I can tune in some fm stations. I have it wired according to schematic but I am curious about the 10uf cap with the + side to ground. I have an extra tube which supposedly checks good so I should be OK there. Any thoughts?


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