[Amps] Auto tune conversion using stepper motors?

[MU 4CX250B]

Markku,
Stepper motors will work just fine for your application. Yes, one
initializes the motors at power on, and then there is no need for
additional control feedback. Initializing is easy with air variable
capacitors, but a bit tricky for a multi-turn vacuum variable. I'm not
sure current sensing will work effectively with stepper motors.

Size 23 stepper motors should be strong enough to turn a vacuum
variable, but commercial amps (eg Alpha 9500) generally use a smaller
size with gear reduction. it is obviously necessary to remove the
detent on rotary switches.
73,
Jim W8ZR

Sent from my iPhone

> On Apr 25, 2014, at 1:24 AM, Markku Oksanen <ww1c at outlook.com> wrote:
>
> All
> I have a home brew GU-84b amp that I don't seem to be able to sell so perhaps I keep it and upgrade a bit.
> The question is: Do stepping motors, properly used, big enough, etc. keep their position information accurate so that they can be used to tune the amp?  I already have the band switching done with the B1B and B2B Russian RF relays and both the tuning caps are vacuum so stepper motor step size will not kill the idea.  The conversion gets a lot more complicated if I need position feedback such as potentiometer.  I was just thinking perhaps at every power up running the caps to the limit with current sensing on the motors so that the limit is detected (or is it?).   What is the proper way to do this?
> I was searching the net for multi-turn (more than 10) hobby servos but didn't find any.  Naturally a proper pair of servos would solve this nicely.
> Thanks!
> MarkkuOH2RA/OG2A/WW1C
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