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

[zendoc at netspace.net.au]

Don -

Thanks - that 's exactly what I needed to know.  I've  measured an
open circuit voltage of 16.2VDC at the amp keying RCA jack and current
of 116mA when the relay is closed.  These parameters are well below
the limits of the K3 keying circuit, so I'll remove the buffer
interface unit.

I see from the AL-811 schematic that there is a 1N4007 across the
relay, which is there to block any back EMF pulses from being applied
to the keying line, I guess.  That was my other concern, whether
these transients would damage the K3, but I guess the amp designer put
the diode there for that.

I'm only using this amp for SSB phone, so QSK is not needed.  My amp
is nearly 25 years old ( 3 owners now) - it has the original open
frame relay:  slow and noisy, but still reliable.

What I'd REALLY love, of course,  is a KPA 500 :)   But this old
AL811 is humming away perfectly on a set of 572b tubes and I don't
have the heart to get rid of it until something expensive goes wrong.

I'm off to rationalise my shack wiring - one less black box!

73,
John
VK7JB