[Amps] Amplifier with Remote Capability

[JMLTINC at aol.com]

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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