[Amps] Tuned inputs

[Phil Clements]

> Roger, I've never personally had that problem with anything other than the
> 3CX3000 amp with that Henry un-un in the circuit, so put it down to some
wierd
> effect from the un-un.  Both the FT1000 and IC7800 do the same thing but
are fine
> into other non-perfectly-matched loads.  Theoretical explanation, anyone?

Henry 8K/3K Ultra Operating Manual; page 40:
"With some transceivers, particularly those with built in antenna tuners, we
have found that some of them cannot get a good match in AUTO mode. If you
turn off the automatic antenna tuner, and run the transceiver directly to
the 3KU or 8KU, you should have no problem."
This should be obvious why the AUTO tuner does not work; unlike a fixed
load, as an antenna or dummy load, the input impedance of the tube is
constantly changing during operation, and the tuner searches for a match
every time the impedance changes. This is like a dog chasing its tail. Henry
guarantees an input vswr of 2.0:1 or less. Typical is 2.0 to 1.8:1. The
tuner on AUTO is constantly trying to seek a 1.1- 1.5:1 vswr. By the time it
succeeds at this, the tube input impedance has already changed to another
value, and away the tuner goes again, trying to do its job; a never-ending
exercise in futility.

Your experience with other "non-perfectly matched loads" is just a matter of
luck!

(((73)))
Phil, K5PC