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Philco 640 Bakelite Capacitor Issue
#1
I am working on re-caping a 640 and ran across a discrepancy. Under the replacement parts section part 44 is listed as 3615-DU which is a dual .05uf ungrounded block cap.  The actual part used in the radio is a 3615-DG which is grounded.  I did not look closely when I pulled out the guts but I assumed that the two caps shared pin 1, which is grounded.  If this is the case than the schematic as drawn is not correct as it shows that the pair of caps connect to the 78 cathode, not ground.

Is the schematic wrong? Could the dual caps share pin 3 which would allow the schematic to work as drawn but this goes against the dual caps I have worked on before and what is shown in Fig 1. If the the 3615-DG was used by accident vs the ungrounded part I would expect that the 300 ohm resistor would have a lead wire going to the chassis for the ground, it does not, it uses pin 1 for the ground suggesting that the 3615-DG is the correct part to use.

[Image: https://i.imgur.com/GtoNvCJ.png]

[Image: https://i.imgur.com/zatNwzH.png]
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#2
I think the sch has a mistake and the two caps should share the GND, the second cap being the filter along with the resistor 45 for the IF stage plate power.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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#3
Welcome to the Phorum!
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I don't have a 640 so can't look to see what's in the chassis but I have come across a bakelite block cap that was wired differently than the diagram for that numbered block (I don't recall which model radio that was). Let's see what some of the pholks that have actually worked on a 640 have to say.
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#4
Thanks for the welcome.  I  guess I am NOS as I once had an account probably 10 years ago and got a lots of help on a model 60 I completely down to a bare chassis and then restored.  My login was lost over the years but now here I am getting back into the hobby.  My other current project is one of those other brands, a 9-s-262 which has a very good rebuild log on this site.

Thanks again, Brad.
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#5
Welcome back!
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#6
I think Mike is correct. The left side of the upper .05 cap should be connected to ground, not to the other .05 cap.  Use the grounded block, both capacitors connected to the ground terminal.

Steve
M R Radios   C M Tubes
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