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Radio played great then nothing

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Radio played great then nothing Empty Radio played great then nothing

Post by bill57 on Fri Mar 11, 2011 11:02 pm

Working on an Automatic P-64 portable. All original caps and resistors. Tube lineup: 1U4, 1U4, 1U5, 1R5, 3V4. Owner I bought it from said it played fine so after a few ohms checks , tube testing and visual inspection I plugged it into an isolation transformer and it came on crystal clear with good reception. I still planned on replacing filter caps but I let it play for about an hour will I worked on the case. Then instead of turning it off at the switch I just flipped off the isolation trans. I came back to it an hour later, turned it on and NOTHING. Completely dead, no tubes light up. Rechecked the tubes, voltage present at the rectifier. It does have a selenium rect and I checked the plus side to chassis with 116V. So what do you think occurred here between turning it off and turning back on and where would you start checking first?

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Post by fifties on Mon Mar 14, 2011 6:42 am

These battery tube sets usually only have one 10 uf filter cap, so I would start by replacing it. If still no go, check to see if you have 1-1/2 v. filament voltage on one of the tubes. If not, pull each out and test for continuity between pins one and seven.
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Post by bill57 on Fri Mar 18, 2011 1:13 pm

OK the first thing I planned on doing with this is replace the filter caps and start checking resistors, etc. So this has the typical filter pack in a can on top the chassis with a black cardboard tube over it. The black cardboard tube has the caps printed on it as: 50mfd/150V, 30mfd/150V, 25mfd/150V, and 200mfd/10V. So I desoldered all the connections and removed the can to restuff it with new. But to my surprise when I removed the cardboard tube printed on the side of the aluminum can is: 40mfd/350V, 40mfd/350V, 20mfd/350V, ans 40mfd/25V. Made by Zenith. It did not appear to have been replaced by anyone in the past so I'm assuming this is factory. I cannot find a schematic on this model to check anything however there is a diagram on the back cover showing a part no. for the caps. This matches the part no. on the cardboard sleeve but not the actual can. So what do you do? Go by the cardboard markings or the markings on the can?

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Post by Bill Cahill on Fri Mar 18, 2011 3:03 pm

I'd go by markings on sleeve. I'm convinced the can is someone's poor replacement.
40 mfd for the filament supply is WAY to low!
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Post by bill57 on Fri Mar 18, 2011 7:49 pm

Thanks, Bill. That is what I think I will do since the part no. is the same on the sleeve as on the radio's diagram. I will try it out and hopefully this will take care of the original problem. The radio did play again the next day and again it would not play after turning off and back on and the 3V4 tube, which did test very good is now bad. So I'll change these caps and put in a good 3V4 and see how it does.

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