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#1
05-24-2023, 06:03 PM
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Pin #1 on a 5U4 Question
Working on this Dumont "Doghouse". Someone replaced a socket for one of the 5U4 rectifiers and did a hell of a botched job rewiring the pins. As I try to untangle the mess, my first question is they used socket pin one as a tie point for two leads from another part of the circuit, essentially as a terminal strip tab. Pin #1 is internally connected in the tube but I don't think it does anything. I've read some threads where it was suggested it's a ground for the metal shell or it's there to physically stabilize the tube in the socket etc....
I'm asking because I'm trying to run down a short when the relay engages. If I leave the rectifiers out of the circuit, the relay closes and everything looks stable. If I wire either of the 2 rectifiers individually in the circuit or together as they're supposed to be, the circuit shorts and the relay goes into a loop of sparking, disengaging, sparking etc. Just trying to eliminate possible issues one by one, could there be an issue using this pin, #1, as a neutral terminal connection point? I would expect the previous tinkerer to have used a tab for pins 3, 5 or 7 as a tie point. So does anyone know why pin 1 is there on a 5U4 and can it be benignly used as a tie point? 
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#2
05-25-2023, 08:12 AM
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According to the Tung-Sol manual, pin one is no connection.
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#3
05-25-2023, 08:23 AM
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I don't think that's the main problem, but you can rule it out fast by removing the 2(?) wires on pin 1 temporarily connecting them together mid air away from the socket and trying it....If behavior is unchanged then trace the B+ loads by unhooking everything at a branch and looking for the path of least resistance and rinse and repeat till you reach the short.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
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#4
05-25-2023, 09:41 AM
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Pin 1 is not connected to any internal connections in any version of the 5U4, so it's just being used as a tie point, but make sure the tube in your socket is actually a 5U4. It's before my times a bit, but there may be a 5T socket rectifier tube out there with pin 1 connected (pure speculation).
Can you post the power supply of your TV? John
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