09-12-2020, 02:03 PM
Good afternoon, Terry.
tl:dr: The only change I'm recommending is as marked in the image here: 41-608 correction. This makes the schematic match the as-built reality of a factory production 41-608 unit.
The long version:
If you re-read the original post, I didn't suggest that -all- the negative connections for 21, 21A and 21B should go to the chassis. 21B is correct as shown but, exactly for the reasons you cited, the negative connection for 21/21A should (and does, as built by Philco) go to another point -- in this case, the chassis.
I'll try to restate and clarify:
1) 21, 21A and 21B are all potted in the same can, marked 30-2488S on the side, also marked 30-2488 on top of the can. Upon dissection, 21B is completely isolated, having its own negative lead (the yellow wire). 21 and 21A have a single, -common- negative lead (the black wire) coming out of the can. This agrees with the printing on the side of the can, and this is why there are only 5 wires exiting the can, not 6. There is no internal electrical connection between the can and any of the caps.
2) As manufactured, it's impossible for 21 and 21A to be wired according to the schematic. They have a single, common negative connection (the black wire as stated in #1 above), but they are shown connected to two, electrically separate points (chassis for 21, jct. of the 26 ohm/28 ohm on 77 for 21A) on the schematic. In reality, factory wiring has their common negative connection (black wire) to the chassis, which is exactly how the 41-250, for example, is wired.
3) Opinion: Even if it was possible with the original part, I don't think there's a good reason to bias the negative side of 21A below chassis ground, and it may even be detrimental to the operation.
See what I'm saying?
Cheers!
-Brian
tl:dr: The only change I'm recommending is as marked in the image here: 41-608 correction. This makes the schematic match the as-built reality of a factory production 41-608 unit.
The long version:
If you re-read the original post, I didn't suggest that -all- the negative connections for 21, 21A and 21B should go to the chassis. 21B is correct as shown but, exactly for the reasons you cited, the negative connection for 21/21A should (and does, as built by Philco) go to another point -- in this case, the chassis.
I'll try to restate and clarify:
1) 21, 21A and 21B are all potted in the same can, marked 30-2488S on the side, also marked 30-2488 on top of the can. Upon dissection, 21B is completely isolated, having its own negative lead (the yellow wire). 21 and 21A have a single, -common- negative lead (the black wire) coming out of the can. This agrees with the printing on the side of the can, and this is why there are only 5 wires exiting the can, not 6. There is no internal electrical connection between the can and any of the caps.
2) As manufactured, it's impossible for 21 and 21A to be wired according to the schematic. They have a single, common negative connection (the black wire as stated in #1 above), but they are shown connected to two, electrically separate points (chassis for 21, jct. of the 26 ohm/28 ohm on 77 for 21A) on the schematic. In reality, factory wiring has their common negative connection (black wire) to the chassis, which is exactly how the 41-250, for example, is wired.
3) Opinion: Even if it was possible with the original part, I don't think there's a good reason to bias the negative side of 21A below chassis ground, and it may even be detrimental to the operation.
See what I'm saying?
Cheers!
-Brian
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