|[AMRadio] Keying a Gates BC-1?|
w5omr at cox.net
Mon Apr 18 06:26:35 EDT 2005
DAVID AABYE wrote:
>Greetings Heavy Metal Enthusiasts,
>I'm trying to determine how best to place the
>oscillator in standby during periods of receive.
>I have two main concerns. One is protection of the
>833's if plate voltage is applied without drive. The
>second is avoiding excessive cathode-to-filament
>voltage in the 807 audio drivers (cathode followers).
>Perhaps both worries are more imagined than real?
Well no, Dave. At least in the case of having full B+ applied to the final.
You absolutely need bias voltage, of course(*). If the final is Biased off
at the proper place, for the proper class of operating, then you -should-
be able to to leave the B+ on the final, when there's no drive.
(*)In my case, with the 250TH rig, when proper drive voltage is applied,
the grid current developed (between the grids of the push-pull balanced
tank circuit and ground) passes through a contactor relay, which when
closed, provides the AC path for the primary voltage for the plate
transformers. This way, with no bias voltage on the grids of the final,
the B+ can -not- be applied, unless there's sufficient grid drive.
If you'd really like to stop both from happening, then just open the center
tap (aka ground return) through a relay. When the relay is closed, that
then makes the ground connections for the voltages to flow, through both
the plate transformer for the 833's and the audio driving transformer for
>Anyway, please share your experiences. Any advice
>will be much appreciated.
Hope that helps. Of course I must warn you, I'm typing this at 5:30am, with
no coffee yet, on a Monday morning. If you mistakes, or see that I any
out, forgive me.
>73 de Dave, W4QCU
>Oak Ridge, TN
73 = Best Regards,
(/5 New Orleans, LA)
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