Mono Tuner output into Stereo Input

It should work fine.

Or rather than use a y-adaptor, you can buy a y-cable that will do the same thing with one less connection. It isn't something you need to spend a lot of money on.

Depending on the out-put of the tuner and the in-put of your pre, it should work fine. Of course, you'll have two channels of mono, not true stereo.

Thanks guys. I figured that was the way to do it.
I will probably search for some Y-cables rather than
use the adapters, cleaner, & less connections in the way.
the Tuner is an old HH scott LT10 (tubed) & is in prestine
condition. I changed out the multi Cap, & may change some of the smaller caps since the unit is so old.

I gave up trying to find a Stereo multiplex (Tubed) unit,
they are kind of elusive to find. So I will just go with
Mono for now.

You shouldn't need a scott multiplexer. Find a Heath, fisher, pilot, lafayette, realistic or ???