[TMC] VOX

[WA5CAB at cs.com]

Larry,

TMC documentation can be confusing.  But after several minutes of looking 
at what the front cover identifies as the Model VOX and the O-330/FR manual, 
I finally came to the conclusion that I was looking at the schematic of the 
VOX-2 you have.  

Probably the reason that you would still have detectible output with the 
HFO switch S103 ON but the output control fully CCW is that V203 (6AQ5) has 
some throughput even at zero screen volts.  Switching S103 to OFF should kill 
that.  If you still have output at the frequench of the VMO it is leaking 
out of the unit some way.  The VMO is wired to run all the time.

What I would do, which would be both easier and cheaper than getting into 
the VMO and adding a relay is to either (a) add a DPST switch beside S103.  
Or (b) replace the SPST S103 with a 3PST.  In either case, two of the poles 
of the added switch would be inserted in the leads from B1 and B2 to pins 1 
and 3 respectively of the 6-pin J101.  The added DPST switch would kill the 
VMO without killing the HFO/Amplifier/multiplier so that you could use it in 
crystal controlled mode.  The 3PST switch would kill the VMO and the HFO.



In a message dated 2/6/2010 12:44:30 PM Central Standard Time, 
Telegrapher at att.net writes: 
> 
> I currently have in operating condx a VOX-2.  Only problem is that the HFO 
> and VMO run continuously as it should.  Even turning off the "HFO" power 
> (B+) i still get a considerable signal out of it and so it affects the 
> receiver a lot.  Interference is the word here.  
> 
> What i'm thinking is that in order to curtail this radiation a method of 
> turning on and off of the HFO 6C4 is in order.  Something like opening the 
> cathode of that tube and then turning it back on with an externally 
> controlled relay. 
> 
> I know i have left out a lot of details about this so consideration is 
> what i'm asking for.  I have a very nice adjustable signal that reads as high 
> as .9 on the 1.0 ma scale able all the way down to 0.  It makes no 
> difference in the receiver though as it's almost like a tube is not being cut off 
> allowing the signal to pass through.  BUT, this type of operation would not 
> have been a problem when in commercial service if they were used in a split 
> frequency operation.  In ham service though it is noticeable and 
> irritating.
> 
> This is a nice unit and puts out almost 2 watts so would be a nice qrp 
> transmitter also, kind of big and awkward so a real boatanchor.  Once again 
> though a method of cutting off the VMO/HFO to eliminate the constant carrier 
> output is a requirement.
> 
> Any designers out there with suggestions or objrectins?
> 

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480