KX3 and Chinese MX-P50M 45w amp

[MIKE ZANE]

Need a little help. I just bought a KX3 and have it working OK. I also have a 45w amp that I would like to work with the kx3. However, with no info on the keying line coming from the amp, I have no idea if its Ok to use. I see in the Elecraft manual that the "keyline" and tip would be used to connect to key the amp. I can't which of the sections on a TRRS jack to use. Ring 2 or ring 3? Also  don't know how much current is on that amp key line. Measured 15V DC when it is on and off measured 400 ohms, if that is any help. Any one got any ideas on this? Thanks,  Mike
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[Elecraft mailing list]

Mike,
I have a MX-P50M and when Keyed from the Keyline on ACC2 (on the Ring and
Sleeve of ACC2) works. The spec on the Keyline is 30V, 100 mA max, open
drain. If hooked up the two work fine, with the KX3 set to 5Watts.

However, I did blow the 2n7002 transistor that drains the Keyline at ACC2,
which I cannot attribute to the P50M. It was a PITA to replace, the
replacement of the MOSFET itself is easy, but peeling off all the stuff to
get to the underside of the KX3 RF board and putting all the layers back
together is a b*t**.

I now have a keying buffer that you can buy from RadioDan on eBay. The Kx3
plugs into the buffer, and the other end of the buffer plugs into to the
PX3. If you need more details, please just ask.

73 de k1jbd
Bammi



> Need a little help. I just bought a KX3 and have it working OK. I also
have a 45w amp that I would like to work with the kx3. However, with no info
on the keying line coming from the amp, I have no idea if its Ok to use. I
see in the Elecraft manual that the "keyline" and tip would be used to
connect to key the amp. I can't which of the sections on a TRRS jack to use.
Ring 2 or ring 3? Also  don't know how much current is on that amp key line.
Measured 15V DC when it is on and off measured 400 ohms, if that is any
help. Any one got any ideas on this? Thanks,  Mike



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[Bob Wilson, N6TV]

On Thu, Sep 24, 2020 at 7:52 PM MIKE ZANE <[hidden email]> wrote:

> Need a little help. I just bought a KX3 and have it working OK. I also
> have a 45w amp that I would like to work with the kx3. However, with no
> info on the keying line coming from the amp, I have no idea if its Ok to
> use.


See https://www.hfunderground.com/board/index.php?topic=29686.0


> I see in the Elecraft manual that the "keyline" and tip would be used to
> connect to key the amp.


On the KX3, the ACC2 connector (a 2.5 mm stereo or "TRS" jack), TIP is PTT
IN (for a footswitch or computer-generated PTT if you set *ACC2: IO* to
*LO=PTT*), and ring is KEYLINE OUT (for an amplifier).  So RING of ACC2 is
the one to connect to key the amplifier relay with a KX3.

I can't tell which of the sections on a TRRS jack to use. Ring 2 or ring 3?


The only TRRS jack on the KX3 is the MIC jack.  Ring 2 is Logic Ground and
Ring 1 is PTT IN (push-to-talk switch) or UP/DOWN.  Do not connect the mic.
jack to the amp.

 Also don't know how much current is on that amp key line. Measured 15V DC
> when it is on and off measured 400 ohms, if that is any help.


Just put your meter into "AMPS" or "MilliaAmps" on the highest scale, and
measure the current across the KEY IN or "RELAY" jack of the amp with the
meter while it is powered ON.  The amp. should go into TX mode when the
meter shorts that terminal to ground.  Chances it's well within the limits
of the KX3 KEY OUT line (30V, 100ma max).

BTW, the S-BOX or S-BOX-USB makes a nice "docking station" / computer
interface for a KX2 or KX3, if you need one.  Rig control plus
computer-generated CW and PTT over a single USB cable can be provided,
along with all the required interface cables.

https://www.kkn.net/~n6tv/S-BOX/Features.html#KeyingExampleKX3

73,
Bob, N6TV
https://bit.ly/S-BOX
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