[Elecraft] [K3] Need +12V on TX

[Wes Stewart]

I modified the L4 because I didn't want to fry my TS-870 keying circuit.  I know how the unmodified L4 works, BTW.

I have already kludged a circuit in-line using a PNP transistor and a few resistors, picking up the +12V out of the K3 and the Key Out line and providing the necessary keyed 12V.  This will have to do until I get around to my vacuum relay QSK/electronic bias switch mod for the L4.

What a difference 10 dB makes.  Life is too short for QRP.

Wes  N7WS

--- On Sat, 9/5/09, Guy Olinger K2AV <olinger at bellsouth.net> wrote:

From: Guy Olinger K2AV <olinger at bellsouth.net>
Subject: Re: [Elecraft] [K3] Need +12V on TX
To: "Wes Stewart" <n7ws at yahoo.com>
Cc: elecraft at mailman.qth.net
Date: Saturday, September 5, 2009, 7:35 PM

It is getting quite rare for the transceiver to SUPPLY 12 volts to key
an amp.  All the currently manufactured amps require a GROUND to key
an amp, the AMP supplies a voltage to be keyed, INCLUDING an
unmodified L4B using the "VOX" lead, which is the equivalent of the
more familiar "relay" lead on Ameritron and others.

>From the schematic, the L4B would have expected a ground on the
non-ground VOX lead to key the amp. Since from the schematic, this
would have been a positive DC voltage less than 200 volts, the K3
should have keyed it fine as is.  There is a caution about reversing
the plug in the manual, which was not keyed in any particular way, and
COULD have put a permanent key to the amp if reversed and the
transceiver end was grounded in operation. Drake was expecting a relay
in which the orientation would not matter.

Why did you modify it?

73, Guy.


On Sat, Sep 5, 2009 at 1:05 PM, Wes Stewart<n7ws at yahoo.com> wrote:
> I added a solid-state relay driver in my old Drake L4-B that requires +12V (or so) from the transceiver on transmit.  My trusty TS-870 supplies this signal.
>
> I'm getting tired of running QRP with the K3 and would like to be able to use the amp with my K3 without further fuss.  Is there a magic way to get this signal from the K3 or am I going to be forced to mod the amp again, kluge another circuit in-line, or forget the idea and stick with the '870?
>
> Wes  N7WS
>
>
>
>
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