Quote:
Originally Posted by Don Lindsly
Sound trouble on that TV usually comes from a bad [detector] transformer (32-4631-1). There should be plenty of those around. Make sure you have eliminated the usual suspects like the 6AU6, 6T8 and the 2uf electrolytic under the 6T8.
Don
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I'll take that a step further to say that the two silver-mica capacitors hidden inside the shield of that p/n 32-4631-1 sound detector transformer are the typical underlying cause of sound trouble in those sets & also make a small correction to the quote of Don's comment. Philco p/n 32-4631-1 is actually a
ratio detector transformer, but mica capacitors are often hidden inside discriminator transformers & other transformer, trap, & tank circuit assemblies used in sound i.f. circuits, often without any moisture-resistant coatings. Those capacitors tend to be significantly less reliable than ordinary mica capacitors because of the open construction. We call 'em "naked micas" around here. Not all, but definitely some, makers of aftermarket substitutes for that coil designed their versions using failure analysis data from original units to determine that their versions could be made more reliable by using coated silver mica caps. The absent, weak, or noisy audio often observed as symptoms on these has become known as "silver-mica poisoning" effects. Leakage & value drift are common with the originals, including improperly-stored NOS original replacements.
Does anyone know what capacitor values Philco used inside that unit? We tried 33pF & 47pF (often-used sizes in Admiral & other brands) in a set we're currently servicing, but those values are incorrect for this set & (if I recall correctly) from a discriminator rather than ratio detector circuit. Capacitor values vary for split versus intercarrier & for discriminator versus ratio detector circuits, & will also vary according to winding inductance values chosen by individual set manufacturers.