[AMRadio] Keying a Gates BC-1?


Geoff/W5OMR 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
the 807's.

>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 
words
out, forgive me.

;-)

>73 de Dave, W4QCU
>Oak Ridge, TN
>

73 = Best Regards,
-Geoff/W5OMR
(/5 New Orleans, LA)




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