[ARC5] ARC-5 TX problem --DC on fils gives hum on signal?

[J. Forster]

Maybe a ground loop with your supplies? Or possibly a transformer near
something sensitive?

-John

============



> Have been working to clear up a hum problem on my 3-4 mHz BC-696.  It has
> been converted from 24 volts to 12 volts on the filaments.  The tube
> lineup is orginal:  1626 plus 2 ea 1625's.  In my situation, I supply
> filament power to all three tubes; however, I am only supplying power (150
> VDC) to the oscillator.  No power is applied to the PA plate and screen.
>
>
>
> When I key the oscillator, I can hear the hum in my receiver.  There is no
> antenna connected to the ARC-5.  I am just supplying 150 volts B+ to the
> oscillator and 12 volts to all filaments but I just key the oscillator.
>
>
>
> I've tried various combinations of power supplies for the oscillator and
> 12 volts DC and AC voltage to the filaments, and have determined thereby
> that the hum is being produced by the 12 volts DC and not either the 12
> volts AC or any of the +150 power supplies I tried.
>
>
>
> Said differently, I hear no hum on the signal when using 12 volts AC on
> the filaments.  However when I use 12 volts DC, from a well filtered power
> supply, the signal definitely has audible hum.
>
>
>
> Why in the world would 12 VDC on the filaments cause hum and 12 volts AC
> not?
>
>
>
> Any help or suggestions would be most welcome.
>
> Thanks,
>
> -Tom  KE4RHH
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>