there are many
but george meyer av is a very good one
you can also try scott richardson - he works on older tube amps, see if he will look at yours
Recommend repair tech in so Cal
My Icon st 40 mk4 has died. Power tubes still glow but input tubes don’t and light in bias meter not working. No sound at all. Checked fuse on back near power cord. I would rather not have to ship this thing so I’m looking trusted repair techs in So Cal, preferably near Riverside but willing to drive further.