[ARC5] Grid Blocked Keying an ARC-5 or full break in with cathode keyed VFO

[millerke6f at aol.com]

I'm curious to know how many of the Command Set fans have tried the scheme to decouple the command set transmitter's VFO cathode with a capacitor to the vfo tank and then couple that cathode via a 2.5 MHy choke to the 1625 cathodes for a full break in scheme.  I think this scheme was covered in one of the CQ conversion books.  I used this scheme on an 80 meter unit back in the early 60s on an FD setup and it worked quite well.  In one arrangement I added a 250 ohm resistor to the 1625 cathode returns to run them in a kinda pseudo class AB  and keyed the vfo only with a manual T/R toggle switch.  This was an attempt to minimize TVI by not drawing as much grid current.  I don't recall if the TVI solution was worthwhile, but on that FD I managed to work nearly all states with this unit using a MONSTER DAQ receiver on the bottom of 80 CW.  For those that never saw a DAQ receiver, it was about 8 cubic feet of aluminum that required at least 3 mates to pack up and move. One of those rare moments when the receiver outweighed the transmitter by at least a factor of 20X.

73
bob, KE6F


-----Original Message-----
From: Bill Cromwell <wrcromwell at gmail.com>
To: arc5 <arc5 at mailman.qth.net>
Sent: Mon, Jan 13, 2014 7:17 pm
Subject: Re: [ARC5] Grid Blocked Keying an ARC-5


On 01/13/2014 09:55 PM, Kenneth G. Gordon wrote:
> Sounds good, Doug. Let us know your results. However, one thing I left 
> out of the previous discussion: be sure to ground the + (plus) sides 
> of the full-wave bridge rectifier and the electrolytic caps, leaving 
> the - (negative) sides completely UN-grounded and hard-wired 
> "through", so you get a NEGATIVE 120VDC out of your supply. In such a 
> supply, the negative side is the "hot" side. Connect your resistor in 
> the "hot" side, between the two negative leads of the caps. It will 
> look "funny" to you, since the electrolytics will look like they are 
> "upside down"...but they ain't. If you are using a tube-rectifier like 
> a 5Y3, you ground one side of the filament, and use the center-tap of 
> the transfomer as your negative voltage output. The filter is the same 
> as the SS version: + (positive) sides of the caps grounded, - 
> (negative) sides connected "through" with the resistor (or choke) 
> between them. If your 120 VDC is positive, you will blow up your 
> tubes. Kenneth G. Gordon W7EKB "Courage is being scared to death but 
> saddling up anyway."--- John Wayne

Grid blocking gets even better. It can be used to also control the 
receiver shifting from receive to "standby" and setup to allow the 
receiver to hear your transmitter instead of using an artificial 
sidetone. Electronic T-R antenna switches block use transmitted RF to 
block the grid (or gate) of the switch tube (or FET), too. Are you ready 
for more fun?

73,

Bill  KU8H
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