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Need +12V on TX

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n7ws

Need +12V on TX

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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Guy, K2AV

Re: Need +12V on TX

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<[hidden email]> 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
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html
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n7ws

Re: Need +12V on TX

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 <[hidden email]> wrote:

From: Guy Olinger K2AV <[hidden email]>
Subject: Re: [Elecraft] [K3] Need +12V on TX
To: "Wes Stewart" <[hidden email]>
Cc: [hidden email]
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<[hidden email]> wrote:

Guy, K2AV

Re: Need +12V on TX

> This will have to do until I get around
> to my vacuum relay QSK/electronic bias switch mod for the L4.

That's really where you want to be. But the old rig will still fry it
unless you build two keying circuit inputs.

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

Fighting words for some on this reflector :>)

73, Guy.
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