Passive volume control and line switch, looking for advice

In an earlier thread, I asked about remote volume control of my valve amp system, and two routes were suggested: put a remote controlled pot into the amp, or add a passive volume control.
I'm a little nervous of the electronics work inside the amp, being a complete novice, so I'm exploring the passive volume control first.
There is another ideal requirement, that the amp can be turned on and off remotely. My husband is terrible at leaving it switched on all night.
I'm looking at a 2 channel device on EBay:
https://www.befr.ebay.be/itm/125984...wpu5/e89DsLEHbEL5gUSvJyeU=|tkp:Bk9SR8KPg86WYw
I'm just wondering if I could use the second channel to control a mains switch to turn the amp on and off.
What do you guys think?
 

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It should work as long as the second relay can handle the voltage and current load you're planning on switching. The numbers on those relay cases are very blurry on the listing photo. Worst case, you might need to either add a second relay or find one with the same trigger voltage that can handle line voltage and needed load to replace the one that's on there. You could even move that relay off the board and nearer to the line input to keep the line voltage away from the signal components, a generally desirable aspect of design.