Philco 84 schematic error and confusion - Printable Version
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Philco 84 schematic error and confusion - Patrick - 03-07-2021
The schematic below from an 84 shows a CT (5) on the filament windings of the power transformer to the CT (8) of the 80 plate windings.
The transformer is a 32-7180, also used in a 37-84, which looks like the same chassis, doesn't have that CT. I took the transformer apart, and there is no evidence of there ever being a CT on those windings.
And if you compare the 1934 84 to the 1937 84, the only difference is that CT, AND the .015 cap #32 is not there.
[Image: https://i.imgur.com/SjwLlWT.jpg]
RE: Philco 84 schematic error and confusion - Radioroslyn - 03-07-2021
Ok so the difference two things.
1. By having a ct on the ac heater winding it's use to balance the 60 cy out hum.
2. By not having a ct it's cheaper as you can save on the cost on wire to connect one side of the heater back to the transformer rather than just grounding it.
Sets that use a regenerative detector are prone to pickup hum from any sort of ac field so shielding and decoupling are important. It's akin to a tube in a high gain audio amplifier. Put your hand near it and it hums. Wack it with your finger it rings like a bell. Both the high amp and regen det are typically on the hairy edge of stability do to they high value control grid resistor.
RE: Philco 84 schematic error and confusion - RodB - 03-07-2021
The note below the schematic says cap #32 is only installed in early sets. We've seen this before in early sets where there is a bypass cap across the ps field choke.
RE: Philco 84 schematic error and confusion - Patrick - 03-07-2021
Didn't see that. Old men need big print.
RE: Philco 84 schematic error and confusion - RodB - 03-07-2021
Yep, it definitely says 82.