David Jensen wrote:
I did a search for Mortronics in Google and found nothing helpful. Could
you be more specific or give me a link to a site that sells the products
that you are talking about? Thanks.

Mortronics made (and pretty much originated IIRC) stepped autoformer wall mount volume controls. Instead of a resistive pad (crunching noises, heat, etc.) they used a rotary switch with tapped autoformer(s) behind it. Sonance, Niles, and others now sell nicer packaged variants of the design but Mortronics used to be the only source for 25V and 70V flavors.

I still have a bunch in the garage, not sure how many are 70V models.