[Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

[Guy Olinger, K2AV]

>From the K3 manual:
KEY OUT (RCA/Phono) is the amplifier T-R relay keying output, capable of 
keying up to +200VDC @ 5A.

You do not need the buffer for any Ameritron amplifier. In particular the 
AL-80 schematic shows the Relay jack connected to the 12V bus.

Leave the K3 key out jack connected directly to the AL-80 relay jack, and 
enjoy life   : >)

73, Guy

----- Original Message ----- 

From: "Alfred Frugoli" <ke1fo at arrl.net>
To: <Elecraft at mailman.qth.net>
Sent: Tuesday, June 02, 2009 9:55 PM
Subject: [Elecraft] K3 Ground Loop Issues using Ameritron ARB-704


> I've just gotten my K3 built and integrated into the shack about a week
> ago.  Operated WPX CW this weekend with GREAT success.  Was very happy.
>
> Tonight in setting up FSK, I was getting a lot of "AGN?" after my cq's.
> Listening to my signal on a 2nd receiver, I realized that my signal had a
> hum on it - basically sounded terrible. Tested in CW mode as well, and the
> hum was also there (haven't dug out the mic yet for the dreaded SSB mode 
> to
> know if the hum was there as well, but I would suspect it would have 
> been).
> Tried changing a bunch of menu settings to no avail.  Then I disconnected
> everything from the back of the K3 except for the antenna, power and FSK
> input.  Beautiful clean signal.  The hum reappeared when I connected the 
> amp
> keying line.
>
>  I've been using the Ameritron ARB-704 Amp Keying buffer, and even though
> the K3 can handle the relay voltage on my AL-80 (the key voltage is not in
> the AL-80 manual, but I believe it's 125v), I've kept in in line.  However
> this seems to be the item causing the hum.  When I take it out of the 
> line,
> and connect the rig directly to the amp, no hum.
>
> My shack is NOT well RF grounded, and things are not bonded together at 
> this
> point (that's a needed project - but the ARB-704 doesn't have a ground 
> post
> to connect to - I'd have to go directly under one of the case screws to
> ground it).
>
> Anybody else experience this?  Am I correct in my deduction that the K3 
> key
> out relay will handle the relay voltage on the AL-80?  If so, I'll just
> ditch the ARB-704 for now.
>
> Thanks.
>
> 73 de Al, KE1FO