Help me identify an amp

Carlsbad2 - Absolutely Not!!! Never ever do that with vintage tube gear unless you want to risk replacing an expensive and hard to find transformer.

Bring up the voltage slowly on a variac is the right thing to do.

so it may be a GSI modified Dyna Stereo 70 that uses 8417 output tubes

+1 on the variac and nice and slow you don't want to fry the amp especially transformers which are the best part.

connect some speakers, any load, when you power up tube amps

+1 variac - to bring up power slowly/safely to see if working, especially for tube type amps.  

@dungen 

I bet it will sound great.  People are still making mods for the ST 70.

let us know.