[ARC5] Switching the dreaded B+ line.

[J Mcvey]

I'm probably missing the point, as usual, but why not use the native select system - or are you missing one or more of the tx internal relays?
All of the Tx plate /screen/osc B+ inputs are in parallel on the rack. The internal select relays engage the rack osc bus, finals and antenna.Otherwise the tx units are inert except for the filaments.
All three of these voltages are derived from a single 575V source which is controlled by the keying relay in the BC456.
Dave Stinson provided a 'boiled down" system with just a few resistors and a keying relay. It's essentially the same as the B+ Flow diagram in the BC-456 theory section of the manual. 
If you implement it this way, don't forget to include the r-c spark suppression circuit to save the relay contacts.
Many hams left the osc running and did cathode keying , but that modifies the tx which can can earn you stiff penalties from the ARC-5 list, which may be whipping, hanging or being drawn and quartered or maybe even all of the above! 

 

    On Saturday, April 1, 2017 5:14 PM, Leslie Smith <vk2bcu at operamail.com> wrote:
 

 
Good-day all,

I wish to build a control box to switch the B+ line to the PA and
oscillator circuits in the same way that the selection relay (I think
it's K-53 or relay 53) does.  (This is for a BC-457 - soon to become a
BC-696 ... or a pseudo BC-696 ... )  

But what if  relay K-53 has been "pilfered".  Hmmm?  What if I want to
have a control box with a 3 position switch,  "Spot, Receive, Transmit"?
  That would be a useful switch to have on a control box.  

I could, of course, use a relay, wired in the say way as K-53.

OR (this is such a clever idea I can hardly believe *I* thought of it
...)  I can use an enhancement P-Channel MOSFET in place of the relay.  
 I looked in all the usual places and found nothing over -600V and
nothing under $10.oo    Nothing?  Really?  Seems I didn't look very
hard.  Hmmm.  I have tubes full of 900V 5A N-Channel MOSFETS here, but
I've never had the need for a P-Channel device.

Any ideas?  Hmmm?


Les

PS.  I've given up looking too hard.  Last time I looked for something,
(it was the SCR-274 manual) I looked for about 2 1/2  hours.  Nothing.  
Grrrr!  Then I asked here, and bingo!  In less than 5 minues Jim McVey
gave me a link!!  (Less than 5 minutes!!!)    Miracle!  The very one I
wanted!!  

Now we all know Jim is a nice fellow, but why did he have to wait until
I asked?  Why couldn't he just tell me, before I wasted 2 hours?  Jim?  
Hmm?  (Life is very difficult, I think ...)

(Maybe I'll use a PNP pibolar HV transistor switch.  Except no-one makes
pibolar.  Oh, I get it!  I'll use bipolar. )
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