Speaker sharing between Home Theater & Tube amp

What Tube Pre-Amp do you have? Does it have unity gain?

I have two Dynaco ST-70's (L & R), each has the 8 ohm outputs and the two inputs in parallel to give me an almost 60 watts/channel output and a Yamaha RX-A3010 home theater receiver driving a pair of Martin Logan Quest hybrid electrostatic speakers for the front.

What pre-amp are you using for the vinyl?

Are you willing to run the HT through the vinyl pre-amp and amp also? That would be the simplest solution, but it depends on how often the HT system is used versus the 2 channel and how much you are willing to run the Dynaco. You could run front channel pre-outs from the receiver into the vinyl pre-amp. If it does not have home theater bypass, you can put it into another input and just change the volume to a fixed position that balances the levels. Essentially, make your own home theater bypass, with the added step of adjusting the volume to the right level. You can determine that level from the normal volume setup in the Yamaha.

I have the Dynaco PAS-3x for the vinyl preamp going direct to the ST-70's.

Running the HT through the Dynaco is a good idea. The Yamaha does have a pre-out I can feed into the pre-amp. I have to give it a shot.

The only concern I have is that I want to keep the two systems separate. The HT system for movies and all the surround sound effects are needed to have the receiver for them. The receiver's power rating is 120w/ch which is considerably higher than even the paralleled Dynacos at 60w/ch.

Since my family watches a lot of movies and TV, it will no doubt double the usage of the tube equipment.

Maybe I can talk my boss (wife) into a higher powered tube amps to achieve the same level of SPL (Sound Pressure Level) for the action movies that we're used to.

As I was writing this, a Eureka idea popped into my head (first one this week :-). What if I switch the speakers between the two amps with a relay? When the ST-70 is off, there is no power to the relay, so the off position the Yamaha is connected. When I power on the PAS-3X preamp and have the relay coil AC power plugged into the switched AC socket, the relay will activate and it will switch the ST-70 to the speakers. I think this will solve the problem.