Hi Bob,
IMO, The Henry 3K Ultra is a poor example for remote control to follow. I
own one of these amplifiers, and it is a pain to tune - unless you use the
presets.
The problem is the archaic circuitry to achieve remote control. Ultimately,
it come down to lack of proportional control. Picture this:
Both Load and Tune controls (knobs) on the Control Deck are shafted to a
10-turn potentiometer. At the RF deck, the tune coils and the load cap are
turned via chain by DC gear motors. Each gear motor also turns a 10-turn pot
(also
via chain). The wipers of the two 10-turn pots are sent to a split voltage
comparator (741). When the two pots are the same value, the comparator has 0 V
output. When you turn a potentiometer on the Control Deck, the 741 becomes
unbalanced and either outputs a positive or negative (with respect to chassis
ground) depending upon which way you rotate the pot. A classic H-Bridge relay
circuit provides power and direction to the motor(s). The 741 remains
unbalanced until the pot shafted to the motor catches up.
A very simple plan to implement, but hard to use in practice. Suppose you
are tuning up with no idea of where the controls should be - you aren't even
in
the ball park. You turn a Load or Tune control and watch the meters. Nothing
seems to happen, or it does not happen fast enough because the gear motors
turn at one, slow speed - like a slug. If you have turned the control too far,
the gear motor will continue on, to catch up with your setting. So, to
compensate, you turn the control the opposite way, ultimately overshooting
where
the motor currently is, and so the motor now reverses again. Trying to get the
motor to stop on a dime is an impossible process.
The only way to load and tune with any control over the motor is to bump the
Tune or Load control a bit at a time and wait for the motors to catch up.
The whole time the tube is groaning.
The Henry 3K Ultra has an option for Presets. This is basically more 10-turn
pots (one for each Load and Tune preset) that is switched in place of the
manual, front panel Load and Tune controls. This is very effective once set.
So, if you are looking for predetermined (preset) settings, the Henry
approach is an easy alternative (although the cost of 10-turn pots may become
excessive). If you are looking for a remoted manual-tuned amplifier a
PIC/stepper
motor-controlled solution ala the EZ-Tuner by W8ZR may be the answer.
In any event, I have schematics for the 3K Ultra I can scan and email to you
if you so desire. Contact me of list.
-John, N9RF
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