03-02-2023, 02:17 PM
>I've probed the big black transformer (separated from the chassis) and found something like 400 VAC, 5.6 VAC, and 7.8 VAC. According to the Parts Catalog from 1939 it should be 636, 5.0, and 6.7 so is this "drift" a sign of age/degradation? The 5.6 at least lets me see my replacement 6.3 V dial bulb light up. The schematic I've seen only have resistance values (as far as I can tell).<
For those following at home here's the diagram: https://philcoradio.com/library/download...l.%202.pdf Typically transformers don't drift like resistors or caps they short from overload. If the voltages are somewhat high it can be explained by higher line voltage and perhaps not having any tubes installed when testing. The 400vac measurement was that from chassis one plate and the other? Or from plate to plate? If it's from plate to plate that's a little concerning. Check the resistances midpoint (transformer center tap) to each end of the high voltage winding. The two reading should be within about 10-15% of each other. If way different the winding is shorted and transformer is scrap.
Never try to operate the set with the spkr unplugged or the hv filter caps not replaced. Doing so is asking a lot of trouble! You can however remove the 5Y4 tube and check things out just there won't be any hv. Also check the primary of the output transformer. Not uncommon for it to be open (reading in the 20K or more). Should see a few hundred ohms.
GL w/your project!
For those following at home here's the diagram: https://philcoradio.com/library/download...l.%202.pdf Typically transformers don't drift like resistors or caps they short from overload. If the voltages are somewhat high it can be explained by higher line voltage and perhaps not having any tubes installed when testing. The 400vac measurement was that from chassis one plate and the other? Or from plate to plate? If it's from plate to plate that's a little concerning. Check the resistances midpoint (transformer center tap) to each end of the high voltage winding. The two reading should be within about 10-15% of each other. If way different the winding is shorted and transformer is scrap.
Never try to operate the set with the spkr unplugged or the hv filter caps not replaced. Doing so is asking a lot of trouble! You can however remove the 5Y4 tube and check things out just there won't be any hv. Also check the primary of the output transformer. Not uncommon for it to be open (reading in the 20K or more). Should see a few hundred ohms.
GL w/your project!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got it!
Terry
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