[richidoo]

Two of my SS amps both measure 8kOhms @DC when powered off. Neither has output protection.
I don't understand the physics of transistors, but I know someone who does and I will ask him what happens when you give a unpowered transistor amp a 20V enema. 

My tube amp's OPT secondary winding measures 0.5 ohms.

[rajacat]

I wonder if a heavy duty battery switch would work? They have large contacts and the best ones (marine rated) probably use good copper.

https://www.amazon.com/Blue-Sea-Systems-Circuit-Battery/dp/B00DY88WZK/ref=zg_bs_3398691_1?_encoding=UTF8&refRID=JKWHAM44HEVXJGSWHCND&th=1