09-24-2008, 11:54 PM
Im "scratchin" my head on this restoration of this simple small 1949 mod bakelight radio ac/dc Zenith AM chassis.!(hee hee!) Ive carefully replaced all the caps. The sets working with a "intermittent" shorting in-out from full vol to low vol prob in the front-end. This chassis is the simple 5-tuber, 50L6,& following minature tubes lineup of the era. The set is working, audio section is very stong until the vol "intermittently" shuts down drastically. I have re-checked all tube pins, socket connections, etc very carefully. Ive subbed in a known-good set of spare(s) tubes from another good 100% working (similar) chassis. The prob sounds like a bad-resistor trying to correct itself, but all orig resistors check within fairly near specs, or, very close.The orig antenna-coil checks good this time!!!(hee hee)
Ive traced the prob back to the 2-gang mechanical tuning condensers "mica" adjustments, and/or, the possibility of a IF coil intermittent short in one or both the 455kc cans simply by "tapping" on them. Since the orig 1 meg audio taper Vol/on-off control was bad, I already replaced that also. My voltage checks under chassis are all good point-to-point. When I tap on the tuning-condenser, I get full volume then it immediately drop off again to very low volume. Im overlooking something simple here, and hope I dont need to pull the IF trans if not necessary? Your thoughts please. The orig loop antenna is good also, and the set performs very well when the front-end is "intermittenly" working properly for those few minutes after complete tubes warmup. This set has the isolated ground B- , and 5 tube filament string. Any Ideas??
Ive traced the prob back to the 2-gang mechanical tuning condensers "mica" adjustments, and/or, the possibility of a IF coil intermittent short in one or both the 455kc cans simply by "tapping" on them. Since the orig 1 meg audio taper Vol/on-off control was bad, I already replaced that also. My voltage checks under chassis are all good point-to-point. When I tap on the tuning-condenser, I get full volume then it immediately drop off again to very low volume. Im overlooking something simple here, and hope I dont need to pull the IF trans if not necessary? Your thoughts please. The orig loop antenna is good also, and the set performs very well when the front-end is "intermittenly" working properly for those few minutes after complete tubes warmup. This set has the isolated ground B- , and 5 tube filament string. Any Ideas??
