[TenTec] Adding an external VOX for the Model 526

[Jerry Volpe]

I don't know about you but I have never been one to enjoy holding onto a
hand microphone, especially during long 2-meter simplex exchanges.
Looking around my shack I see four Yaesu FM rigs and my Ten-Tec 526....
none of which have VOX capabilities. And only my 526 had a mic connector
friendly to my various desk microphones (all set up for Ten-Tec 4-pin
connections).

Well some months ago it hit me.... just add a VOX circuit to the 526 and
use my Ten-Tec 705 desk mic. Hmmmmmmmmm. Don't want to mod the 526. Junk
box is too bare to roll my own circuit. Do commercially made stand-alone
VOX units exist that don't cost a fortune? Yes.

A couple months back I located a slightly used Icom EX-1514 VOX Unit. It
is small and black and looks very nice with the 526. I think I paid
about $25. Now to make it work with the 526.

Step one was to replace the 8-pin connector and 8-pin plug on the VOX
unit with 4-pin versions and rewire the VOX unit for direct Ten-Tec
usage. Icom mic connectors have receive audio on pin 8. You need a
sampling of receive audio for the Anti-vox circuit. My work around was
to back out a small audio coax from the 4-pin mic connector that is to
plug into the mic jack on the 526 and install an RCA phono plug on that
coax. I then plug that cable into the 526's rear panel audio out
connector. This is a fixed level audio signal so I have to periodically
re-adjust the Anti-vox control if I advance the 526's AF gain control
significantly. Since I rarely change the AF gain this is a small matter.

Problem encountered. As it comes from the factory this little Icom was
suppose to get its operating voltage (8 vdc) directly from the mic
connector on the Icom transceiver that you plugged it into. Well I
crossed my fingers and tried to use the 9 vdc on the 526's mic
connector, but my will alone wasn't enough. The 9 volts on the 526 mic 
connector dropped to about 2 volts with the VOX unit turned on. Of
course the VOX unit did not operate properly.

Step two was then to add a coaxial power jack on the VOX units rear
panel and connect it via a voltage steering diode (1N4001) to the
unswitched side of the VOX unit's Vcc. Then to test it out I put a
9-volt battery on a coaxial power plug (I don't have a 9 volt regulated
power cube available at the moment). Now the VOX unit worked perfectly.
There isn't enough room inside the little ICOM's case for to install a
standard 9-volt battery inside.

Finished modification. It works. No hum too! Now I can sit back
(probably a bit too far back) and talk without having to caress that
darn hand mic anymore!

I don't know how many of these Icom VOX units are hanging around but
there have to be other similar boxes that could be modified. And you
might roll your own!

Next step is to get an external speaker jack on the 526. Normally, I
resist physical mods to my Ten-Tec equipment but not including an
external speaker jack on the 526 was a terrible oversight by Ten-Tec.

73,
Jerry, KG6TT
Fairfield, CA