Repairs for amps an preamps

I'm new to Audiogon but have been in the hobby since 1973. I have, among many other things, two legacy pieces that need repair and am looking for references. One is my Dynaco 400 that was twice modified by Frank VanAlstine. First was the double dyna 400, then, a year later, Frank did his circuit modification. The left channel went out. I see no visible damage. Second is the GAS Thaedra. Every few seconds there is a tick or pop. One buddy said it could be a bad cap. Anyway, I'd appreciate any recommendations regarding repairs. Also, I' be willing to sell either/both to someone who can make the repairs. Thanks!Rich in TN