relay problem on SB-401

[Stewart D. Lyon]

At the request of several, I'm posting my fix for the slow pullin of the T/R
relay on the SB-401.

The problem is that the 1.5K cathode resistor (R135) of the relay amp (V12B)
appears in series with the relay and limits the current through the relay,
causing marginal pullin. My fix is to change R135 to a 13 to 15 V Zener. The
circuit now matches a SB-101 (etc)

The parts you'll need are a 13 to 15 volt, 1 watt Zener diode and a 0.2 uf
capacitor (I used the "resin" type that Heath spreads all over its rigs).

You will be working on the Carrier Generator Board (pg 135).
1) With a clip-lead on top and SolderWick on the bottom, remove the end of
R135 that goes to pin 6 of V12. The ground end of the resistor is buried
under a wiring harness and left alone -- the resistor is left standing in
the air. You could also clip out the resistor but then it would be hell to
put it back.

2) On the bottom side of the board, tack solder the Zener between pin 6 of
V12 (cathode) and a convenient ground (anode).

3) Tack a 0.2 uf cap between pin 7 of V12 and ground. This restores the VOX
delay.

. . . . that's it.

73, Stu W6CUX

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