KXPA100 Keying Mod

[Dave KD1NA]

Everyone.

I had an interesting experience recently. I have a KX3 and KXPA100 ( #519 )
operating in my workshop in my basement. The rig drives my Heathkit SB220
which has the Harbach soft key mod which has less then 1 volt keying
voltage. This allows me to run up to 1000 watts no problem.

A couple of weeks ago a friend brought me his home brew linear to test.
Before connecting his linear to my KPA100 output I checked the schematic
and measured the keying voltage on his linear which was 24 volts dc at less
then 100 ma. When i connected the key line from his linear to the RCA jack
on the KXPA100 interface cable the linear went to key down without any
transmit command from the KX3. I then disconnected the KXPA100 from my KX3
and using the Elecraft keying interface cable to the linear directly from
the KX3, the linear keyed up upon transmit commands from the KX3 normally.
Well I finished testing my friends linear with 10 watts drive and
everything worked fine despite reduced output power.

Later I emailed Elecraft Support and asked them about the KXPA100 keying
problem.
I quickly got a response and a solution to the problem.

It seems that the first manufactured KXPA100 linears below serial number
700 were designed to operate the KPA500 linear which has only a 5 volt
keying voltage. Evidently,There was some problems with keying linear
amplifiers with higher keying voltages so after KXPA100 serial number 700
and above Elecraft modified the keying circuit to accommodate linear amps
with keying voltages up to 30 volts.

I either missed the memo or Elecraft didn't contact those of us about this
problem. Elecraft now has a mod kit that solved the keying problem. The kit
part number is KXPAMDKT2 and is free. It consists of a 4.7K 1/4 watt
ressistor (E500158) and a diode BV19WSTPMS diode (E560076). The diode is
surface mount and the resistor is a leaded resistor. The  instructions are
clear but some may have problems in removing a surface mount resistor (R28)
and installing the diode in its place. The resistor in the kit solders to
existing components.

The reason I am putting out this information is because I didn't know of
the limitations of the KXPA 100's keying input circuit and could have
easily blown that circuit out. Thanks for the bandwidth.
73

Dave Robertson KD1NA
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[riese-k3djc]

Heathkit SB220 or at least my 221 keys from the bias voltage,,, ??? 130
vo;ts or so
I did a complete install of all the Harbach updates and this makes for a
very stable amp. The heath line of anps are a deal,,, 3 to 500 bux as
opposed to
3500 for newer amps

Bob K3DJC





On Thu, 9 Jun 2016 10:43:58 -0400 David Robertson <[hidden email]>
writes:

> Everyone.
>
> I had an interesting experience recently. I have a KX3 and KXPA100 (
> #519 )
> operating in my workshop in my basement. The rig drives my Heathkit
> SB220
> which has the Harbach soft key mod which has less then 1 volt
> keying
> voltage. This allows me to run up to 1000 watts no problem.
>
> A couple of weeks ago a friend brought me his home brew linear to
> test.
> Before connecting his linear to my KPA100 output I checked the
> schematic
> and measured the keying voltage on his linear which was 24 volts dc
> at less
> then 100 ma. When i connected the key line from his linear to the
> RCA jack
> on the KXPA100 interface cable the linear went to key down without
> any
> transmit command from the KX3. I then disconnected the KXPA100 from
> my KX3
> and using the Elecraft keying interface cable to the linear directly
> from
> the KX3, the linear keyed up upon transmit commands from the KX3
> normally.
> Well I finished testing my friends linear with 10 watts drive and
> everything worked fine despite reduced output power.
>
> Later I emailed Elecraft Support and asked them about the KXPA100
> keying
> problem.
> I quickly got a response and a solution to the problem.
>
> It seems that the first manufactured KXPA100 linears below serial
> number
> 700 were designed to operate the KPA500 linear which has only a 5
> volt
> keying voltage. Evidently,There was some problems with keying
> linear
> amplifiers with higher keying voltages so after KXPA100 serial
> number 700
> and above Elecraft modified the keying circuit to accommodate linear
> amps
> with keying voltages up to 30 volts.
>
> I either missed the memo or Elecraft didn't contact those of us
> about this
> problem. Elecraft now has a mod kit that solved the keying problem.
> The kit
> part number is KXPAMDKT2 and is free. It consists of a 4.7K 1/4
> watt
> ressistor (E500158) and a diode BV19WSTPMS diode (E560076). The diode
> is
> surface mount and the resistor is a leaded resistor. The  
> instructions are
> clear but some may have problems in removing a surface mount
> resistor (R28)
> and installing the diode in its place. The resistor in the kit
> solders to
> existing components.
>
> The reason I am putting out this information is because I didn't
> know of
> the limitations of the KXPA 100's keying input circuit and could
> have
> easily blown that circuit out. Thanks for the bandwidth.
> 73
>
> Dave Robertson KD1NA
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[Arie Kleingeld PA3A-2]

Hi David,

Elecraft probably did not communicate it to you. I had a TR-switch
problem in my KPA500. After a good search and some correspondence with
Elecraft  I found the cause of the problem. And ....  Presto, there was
standard mod for it and they did not tell me that beforehand.  I had to
find the rootcause of the problem first. Learned a lot by the way haha.

(Anyway, the KPA500 does a splendid job.)


73

Arie PA3A


Op 9-6-2016 om 16:43 schreef David Robertson:
> I either missed the memo or Elecraft didn't contact those of us about this
> problem. Elecraft now has a mod kit that solved the keying problem. The kit
> part number is KXPAMDKT2 and is free.

______________________________________________________________
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