kevzep
Its all about the Music
If you can't test it reliably on a meter, how do you know if the STV has failed? How difficult is it to make the replacements you reference?
You can test them, with you meter in the diode test setting, if your meter wont respond to measuring one, then you most definitely need a better meter, especially if you are working at this level.
I have never seen a STV3 go bad in the 20 odd years I have been doing this. This includes whole power amps which have completely detonated and fried themselves.
Assumption is the mother of all F ups....
I just measured one with my Fluke 115, they are 1.47V