Hi,
I would guess the Glentek servos are DC motors and the drives are transconductance amplifiers. That would have been common in the 80's or thereabouts.
The drives require an analog input, and that is derived from the control. The number of controllers on the market with analog outputs has severely diminished over the years with really only the expensive ones
like Galil still in the hunt.
Most modern controllers which are both much cheaper, and a much wider choice of makes and models are Step/Direction output (in the main), but such controllers would require you replace the old servos.
Is it your intention to retain the old servos and drives or would you consider swapping the old servos and drives for modern AC servos?
To replace the servos with modern ones is obviously expensive, say $600 to $700 per axis, but that is offset somewhat by a cheaper controller. The advantage is that the Step/Direction controllers are pretty straight forward
as a hobbyist refit.
To reuse the existing servos and drives obviously saves having to buy new ones, so I know that would appeal, but then you'd have to get an analogue controller. Jim has a long and fruitfull history with Galil controllers,
but they are expensive to buy new. There are less expensive brands, but they all (including Galil) have the complication that you need to program and tune PID control loops....not for the faint hearted.
You need to ask yourself whether you have the technical inclination to program and tune analogue servos, as I say, not for the faint hearted. If that sounds overly difficult then new AC servos look like a good solution
but could easily cost 2k.
Craig