[ARC5] Switching the dreaded B+ line.

[Mike Everette]

Leslie,
The K53 selector relay does enable the oscillator by turning on its B plus; but it does not switch any B plus to the final.  It enables the PA by grounding the cathodes of the 1625s, which in unselected mode (relay open) are held off ground by a 51K resistor.
It would be perfectly fine to key the transmitter with this relay, switching these circuits.  Just remember to disconnect the K54 antenna selector relay coil, and close the antenna circuit by using the "spring" contact against the antenna post.
The K53 relay will follow a bug or keyer to better than 25 wpm.
Manually adjust the K53 contacts so that the oscillator B plus comes on before the 1625 cathodes are grounded.  It's easily done.
In the original design, the transmitter is keyed by making and making the master B plus line directly from the dynamotor, before it goes through the voltage divider to derive oscillator plate and amplifier screen voltages.  The original keying relay is inside the BC-456 modulator.
73
MikeWA4DLF

      From: Bruce Long via ARC5 <arc5 at mailman.qth.net>
 To: Leslie Smith <vk2bcu at operamail.com>; ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Saturday, April 1, 2017 9:51 PM
 Subject: Re: [ARC5] Switching the dreaded B+ line.
   
Leslie   With some time I CAN FIGURE OUT HOW TO YOU YOUR 900 V    ( sorry for the caps) n-fets  Can you send me a schematic of the BC-457 or a link so I can see exactly what the relay does?   thanks   bruce

PS Zuzu who is here at my desk working on her math homework  says hello and hopes your lizard family is doing well.


      From: Leslie Smith <vk2bcu at operamail.com>
 To: ARC-5 List <arc5 at mailman.qth.net> 
 Sent: Saturday, April 1, 2017 5:14 PM
 Subject: [ARC5] Switching the dreaded B+ line.
  

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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