Applaud
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Rick Stealey
Sent: Wednesday, February 07, 2007 2:32 PM
To: amps@contesting.com
Subject: Re: [Amps] Drake L4B
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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