[R-390] R-390 filament voltage

[Bob Camp]

Hi

Quick check: 

Are we talking about V505, one of the IF amplifier tubes on the R390 not an A? 

Assuming we are, it’s a 6V filament tube (a 6BJ6). Its filament is in series with some the other filaments on that sub-chassis (V506 and V511). Since it’s a series connection, when you pull one of the tube out, you will indeed see the full 26V filament supply. 

So: to check the voltage, you really need to check things with it in circuit. You may well find one of the other tubes that’s in series with it has a shorted filament. 

Bob

> On Sep 8, 2024, at 8:03 AM, THOMAS SMITH <n5ama at att.net> wrote:
> 
> My Collins R-390 is continuing to throw me curves. I’m in the process of realignment and noticed V505 glowing brightly yesterday. I pulled the tube and checked the pins for filament voltage. Got 0 vac on pin 3 and 26 vac on pin4. I’m assuming the filament voltage check is with tube in place to complete the circuit but I’m confused about the tube glowing brightly all of a sudden. It’s what I might expect with 26 volts on it. I know V505, the two HV rectifiers, heaters etc get 26v but assumed 505 was supplied 12 through circuitry.
> 
> Any suggestions??
> Thanks,
> Tom N5AMA
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