Something Tomm might not know: The Russian vacuum variable caps may have a
diffrent turns ratio(Less turns for more/less C) than other brands like
Jennings,etc.This could affect the final gear ratio used with the stepper
motors.I have a 20-1200pf Russian cap here that requires only 7 or so turns
from low to high C. Jim..
----- Original Message -----
To: <KD7QAE@ARRL.NET>; <email@example.com>
Sent: Thursday, September 15, 2005 12:34 PM
Subject: Re: [Amps] stepper motors
> Hi Tom,
> I've commented on this before... don't recall whether in public or
private e-QSO but, ...
> I've built amps with both stepper motors and gearhead motors. The
gearhead units are easier (less parts) to drive and adapt to autotuning
should it be desired. Though, I will confess to overcomplicating the
stepper implementation by employing sine drive for quiet operation.
> 73 & Good morning,
> Marv WC6W
> -- KD7QAE <KD7QAE@ARRL.NET> wrote:
> I am (still) in the process of designing my dual gs35b amp and would
> like some advice on stepper motor selection. I have 2 Russian vacuum
> variable caps that I want to motorize and wonder if anyone on the list
> has found just teh right stepper to turn these babys. the tougher one
> is the 10 to 1200 pF unit. I can design the controller and drivers and
> will be linking them tothe vacuum relay coil tap selector on the PI
> inductor. The L section taps are selected by a manual switch which also
> sets the gross tuning position of the capacitors and the proper PI tap
> relay. I intend on using rotary digital pots to make the fine capacitor
> adjustments from the front panel and then having the option of storing
> the exact setting as read out from shaft encoders for quick setting in a
> particular rig / amp / antenna setup. Not autotune, but close.
> Tomm, KD7QAE
> PS, the plate choke is now done, removed 20T from one end and replaced
> w/ 5 wide space helical turns. I need some power FT caps for the AC
> wiring section to keep RF off the line cord as much as possible, anyone
> got some?
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