I just replaced my transmitters/receiver with a Genie from Home Depot.
It has rolling digital codes. It comes with a wall-wart transformer
if you need it, but I powered mine directly from the 24 VAC from the
opener itself. BTW, this is the 2nd full replacement since 1972. This
time, the previous receiver got his by a lightening induced spike. I
think it was about $50 for the receiver and 1 transmitter. The 2nd
transmitter wasn't cheap, about $25 or so.

Peabody wrote:
I have a 1972-vintage Sears garage door opener, model 139.654000
which still works great. But the only remote I have left is
falling apart, and is no longer dependable, particularly in very hot
or very cold weather.

The transmitter/receiver system is the old analog type - no digital
codes at all, just the specification of "carrier frequency" and
"modulation frequency", and the receiver is powered by 24VAC
provided from the main chassis. In fact, it appears that the
receiver actuates the opener mechanism by at least partially
shorting out its own power supply temporarily.

I have been unable to find any direct replacements for either the
transmitter or the receiver. In fact, I don't really see any total
replacements for the transmitter/receiver system that would operate
using the 24VAC power supply.

Does anybody have any suggestions for what to do? I'd like to avoid
having to replace the entire opener.