620 electrolytics - Printable Version

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620 electrolytics - GilBenn - 08-09-2012

I found myself a Philco 620 at a flea market. I'm begining restoration. It seems to be in decent shape, but it appears someone had bypassed the the elctrolytic cans with orange cardboard "Atom capacitors" at some piont.
I've restuffed the one can with a (16mf @ 450v), but the other can has me puzzled. The schematic I found shows it should be a multi-section can (8mf -8mf @???). I have two 10mf @350v available to use, but how can I tell if 350v is sufficeient.
I'm still learning to read schematics, but the part listing doesn't indicate the voltage value. Can any one advise please?

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RE: 620 electrolytics - Sparks_Radio - 08-09-2012

I am by no means an expert but these are some alternate ways to find out a ball park figure.

Looking at schematics in both Riders and Beitmans, shows different 620 models such as 37-620 and 38-620 and Bietmans says updated 620.
So I think the solution would be to know the rectifier type and know what the winding ratio is. It seems to be the transformers have a center tapped HV winding of 145ohms to CT and 155ohms to CT and the input is 5ohms So determine the ratio and apply the ratio to input voltage and you should arrive at AC output voltage.
I cannot see the voltage on the secondary clearly but it looks to be Either 660Volts or 860volts. Then look at a tube data sheet and see what the normal operating voltage range is. This should give you a clue to what voltage to consider. I know there is a rule of thumb in voltage for caps but don't remember what it is but I would say at least 20% more that the used voltage. I could be wrong though. I will see if I can find out. They used both a 5y4 but off hand I would chose 450 volts or even a 600volt to be safer. Looking at the tube manual says typical operational voltage 700 to 1000Volts Wow! But with loading and resistances it may be lower.

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RE: 620 electrolytics - Ron Ramirez - 08-09-2012

Hi GilBenn

Capacitor can (67) is a dual 8-8 uF unit. The original was rated 475 volts each section!

I would not use less than 10 uF, 450 WVDC; 500 WVDC would be better as a safety factor. True, the input filter is not likely to see more than 350-400, but I would rather be safe than sorry...power transformers aren't cheap!

The single can was originally 16 uF, 400 WVDC. 22 uF, 450 WVDC would be an ideal replacement.

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