Philco 640 Electrolytic Voltage Ratings? - Printable Version
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Philco 640 Electrolytic Voltage Ratings? - Geoff - 06-10-2014
I'm putting together a shopping list for my Philco 640 and will be buying from JustRadios.com. There are 3 diagram numbers listed as electrolytics:
#68 2 Mfd., 2 Mfd., 1 Mfd. Philco P/N 30-2114
#74 8 Mfd. Philco P/N 30-2025
#75 12 Mfd. Philco P/N 30-2117
The voltage rating is not listed in the parts list. Anyone have an old Philco parts catalog that lists the voltage rating? I checked Chuck's site but those numbers are not listed.
Thanks,
Geoff
RE: Philco 640 Electrolytic Voltage Ratings? - morzh - 06-10-2014
74 and 75 I would go with minimum 500V+ rating, 68 - 450V+ (there is the RC there) but I would still recommend 500V min.
RE: Philco 640 Electrolytic Voltage Ratings? - Geoff - 06-10-2014
According to the schematic (attached) #'s 74 & 75 are attached to the rectifier filament which is supplied voltage by winding 6-7. According to the power transformer data that winding supplies 5 volts at 2 amps. Do I really need a 500V rated e-cap for these?
Plate voltage for the 85 tube should be 102V. That voltage then goes through the primary winding in the audio transformer and to ground through one of the 2 uF e-cap of #68. Do I need a 500V rated e-cap for this as well?
I'm not sure what voltage is hitting the other 2.0 uF or the 1.0 uF.
Just trying to keep cost of replacement parts down.
- Geoff
RE: Philco 640 Electrolytic Voltage Ratings? - morzh - 06-10-2014
Geoff
They are indeed attached to the filament. With one end. The filament is the rectifier output.
Now look where the other end is attached to.
I let you figure this out.
RE: Philco 640 Electrolytic Voltage Ratings? - Geoff - 06-10-2014
Looks like the screen grid of the 42 tubes at 250 volts. Correct?
RE: Philco 640 Electrolytic Voltage Ratings? - gregb - 06-10-2014
The problem Geoff is the 80 tube will be at full conduction within a second or two of turn on and you could have 450 or more volts at the output of that tube untill the rest of the tubes start to draw current and pull that voltage down. Its not that there will be that high a voltage in normal operation. Its a safety thing so you arn't stessing the filter caps every time you turn it on and reducing the life expectancy.
Gregb
RE: Philco 640 Electrolytic Voltage Ratings? - morzh - 06-10-2014
Greg
Jeff had not realized there is high voltage there at all, he thought the voltage there is 5V of the filment voltage.
This is the exercise I wanted him to do first. Once he knows it is not 5V but more like 400V, then we can explain why this 400V temporarily makes an excursion into 500V or so realm.
RE: Philco 640 Electrolytic Voltage Ratings? - gregb - 06-10-2014
I understand your thinking but I am afraid that if Geoff thinks its only 5 volts and puts a finger there he could be hurt.
Gregb