[Elecraft] K3: interfacing with AL-811 amp and buffering...

[Don Wilhelm]

John,

I am not going to give you a specific yes or no answer, but will give 
you and everyone else an answer that will tell you how to check any 
amplifier to see if the K3 will key it without harm.  All you need is 
your amp and a DMM capable of measuring voltage and up to about 10 amps 
of current.

The K3 KEYOUT is rated for +200 volts at 5 Amps.

Turn you amp on and connect it to a dummy load (just for safety to the amp).

Put the positive lead of your DMM into the center connector of the KEYIN 
commector for the amplifier and the negative lead to the shell or 
chassis.  Is the voltage DC positive and less than 200 volts?  If so, 
the voltage rating is OK. If it is AC or is negative, then you will need 
a buffer of some sort.

Next, change your DMM (disconnect one lead from the amp first) to 
measure current - I suggest using the 10 AMP scale (usually you have to 
change the plug on a DMM lead) - again connect the DMM lead you 
disconnected from the amp - the amp should go into transmit mode - read 
the current indicated on your DMM.  Is it less than 5 amperes?

If both those tests pass with Yes answers, then the K3 KEYOUT can handle 
that amplifier.

All that says nothing about the speed of the amplifier relay.  If that 
AL-811 has the original open frame relay, it will not keep up with the 
K3 QSK without 'hot switching' which will burn relay contacts and 
possibly damage the amp's output tank.  Plan to use PTT or install a QSK 
kit in the amplifier.

73,
Don W3FPR

On 8/27/2012 6:32 PM, zendoc at netspace.net.au wrote:
> Hi All,
>
> I would value some advice. Is it necessary to use a keying buffer between my K3 and my old AL-811, or is the K3 keying circuit robust enough not to need this interfacing arrangement?  I currently have an ARB 704 buffer in the keying line, but I'm simplifying my shack wiring and wonder if it's safe to get rid of it. Somewhere in the past, I read of keying line transients and the like and what they could do to sensitive transceivers, but I wonder if that concern is valid in the case of the K3 / AL811 combination.
>
>