What's Wrong With My Filament Circuit? - Printable Version

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+--- Thread: What's Wrong With My Filament Circuit? (/showthread.php?tid=3830)

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What's Wrong With My Filament Circuit? - Pepperoni - 10-13-2011

Same 40-190.
http://www.nostalgiaair.org/PagesByModel/339/M0013339.pdf
I have about 9Vac on my filament circuit unloaded. But when I install the #47 dial lamp in its socket my voltage drops off into the mV range. The socket isn't shorted and has the same 9Vac on it until I install the lamp. I'm just getting the set checked out after a full restoration. The only tube installed is the rectifier so I could look at those voltages. They're good.

But what am I not seeing in my dial lamp/filament circuit? The lamp socket completes the circuit to ground. My ground is good.

EDIT: With my power transformer filament leads isolated I read an open across them. This isn't good but why do I see 9Vac when it's powered up?

Pepper

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Re: What's Wrong With My Filament Circuit? - Chuck Schwark - 10-13-2011

Open fil winding. You're seeing capacitive/inductive coupling to the open winding.
You are seeing a "ghost" voltage when no current is flowing (which can't due to open circuit).

Chuck

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Re: What's Wrong With My Filament Circuit? - Pepperoni - 10-13-2011

Thanks Chuck! Kinda figured that. But already have the old one out which wasn't original to begin with and another from a parts set ready to go. Didn't like the one that was on there anyway. Someone had changed it and swapped the 84 rectifier for a 5Y3. The bad transformer was a 250-0-250 which I was told would work but the new one I'm putting on it is a little bigger and is 350-0-350. Had to remove 1/4" of chassis on the length but otherwise a good fit.

Pepper

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