QRP via ALC on TS-430S


From: James R Giammanco (n5ib@juno.com)
Date: Tue Jan 06 2004 - 15:31:24 CST

After much procrastination I finally sat down to cobble up an ALC voltage
source to make my 1984 vintage TS-430S operate at QRP levels, even on
SSB. The usual method was employed - apply a negative bias voltage to the
ALC input on the accessory connector (pin 6 of the 7-pin DIN on the rear
panel) From here at home there's no way to post a picture or sketch, so
here's a "word picture :^))

The Parts:
9 V battery, battery clip, 100K trimpot, 240K resistor, 1/8" stereo jack,
1/8" stereo plug, 7-pin DIN plug, 18" of RG-174, Altoids tin (wintergreen
preferred, peppermint OK)

The Circuit:
negative battery lead to high side of 100K pot
wiper of pot to TIP of stereo jack
bottom of pot to one end of 240K resistor
other end of 240 resistor to RING of stereo jack
positive battery lead to SLEEVE of stereo jack
SLEEVE of stereo jack to GND (soldered to the bottom of the tin) ...this
is already grounded by the mechanical mounting of the jack, but htis for
the belt *and* suspenders crowd

The trimpot was mounted Manhattan Style, with the pads glued directly to
the bottom of the tin. Press-on Velcro(r) holds the battery to the bottom
of the tin.

The Cable:
inner conductor of rig end of RG-174 to pin 6 of 7-pin DIN plug
braid of rig end of RG-174 to metal sleeve of 7-pin DIN plug
inner conductor of far end of RG-174 to TIP of stereo plug
braid of far end of RG-174 to SLEEVE of stereo plug
........now for the good part.......
jumper between SLEEVE of stereo plug and RING of stereo plug

Plugging the stereo plug into the jack completes the battery circuit and
serves as the ON switch. Removing the plug turns it off and saves the
battery. Battery drain is only about 30 uA so it ought to last a long

 .....next good part.....
(POASBBCSFRM) was applied to the bottom of the Altoids tin. Since the
TS-430 has a ferrous metal cabinet, the gadget is held firmly in place
atop the rig. In operation, power output is now smootly adjustable from
the full 100 W all the way down to under 1 W. It ain't efficient - near 5
A for 1 W :^))
but is IS QRP...

Jim N5IB

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