[Amps] Drake L4B

[Rick Stealey]

Speaking of L4B's you guys got me going on investigating a little problem 
with mine.  I don't know why this started happening because it was ok until 
now, but I noticed the 1000MP started cycling the keying lead about 4 times 
after sending cw.  In other words, when I send cw the 1000MP goes into 
transmit mode and keys up the L4B line, and when I stop sending there is a 
1/2 second delay until the vox relay drops out in the transceiver.  But it 
clicked in on and off about once a second for about 4 cycles then stopped.
I assumed the relay dropout in the L4B was somehow kicking back into the 
transceiver.  I measured the open circuit voltage in the L4B keying line at 
30 volts and keyed it up with a clip lead and yikes! you should see the arc! 
  I tried a diode in series (schematic shows one internal to the L4B as 
well), a diode across the line and an 0.01 capacitor bypass - no change in 
apparent arc size.  So I made up a little transistor switch consisting of a 
PNP transistor and a 1k resistor - bingo, problem solved.  I was amazed how 
simple of a fix this is, and surely the relay in the MP will be much 
happier.  The 2N2905 I used is rated at 60 volts, so it might give out but 
what the heck, if it does I will go hunting for a higher rated one.
All you need is a PNP transistor and a resistor.  The transistor collector 
goes to ground, the emitter goes to the keying line (the plug on the back of 
the amp), the base is connected to the transceiver line through a 1 k 
resistor.  That's all there is to it.  It would be a nice to just 
incorporate the 2 parts internally next time I have it opened up.

Rick  K2XT

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