I have yet to need a re-tube in my svt-3 although I have experiment with different types in a Hartke 3500. Bottom line - I found little discernable difference in the 3500. However the same tubes in my Marshal vs-65 produced much more noticeable differences. For selection I was relying on the advice of a repair tech at a local store - telling him what I had and what I wanted to achieve with the change.
Sovtek, Marshall, Groove tubes happen to be the 3 tubes I had experimented with, and of them, the Sovtek seem to break-up / distort the easiest giving me a nice smooth distortion - not quite as 'grainy' as the original Marshall tube. Consequently the Sovtek has a permanent home in my Marshall. All that said, I later came across this website
www.tubestore.com/index.html - likely someone in this AGB turned me on to it. If your going to be replacing 5 tubes this is the place to get them. Also a lot of great information on how to select tubes.
I have never been under the hood of my SVT-3 but would be interested in knowing who manufactures the tubes Ampeg uses.
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