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 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? _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps ___________________________________________________________________ Try Juno Platinum for Free! Then, only $9.95/month! Unlimited Internet Access with 250MB of Email Storage. Visit http://www.juno.com/value to sign up today!