K3: interfacing with AL-811 amp and buffering...

[VK7JB]

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.  

Thanks and 73,

John
VK7JB

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[Don Wilhelm-4]

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, [hidden email] 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.
>
>

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[vk4tux]

The K3 will handle it direct no issue, with no interface required.