Albertk, is your ST-70 stock, with no mods or updates of parts? How old are the tubes? Their are a lot of things that could be wrong here, but should be fairly simple to fix as long as you can isolate the real problem. It could be a combination of things as well. The hiss may not have anything to do at all with the fact that the tubes don't bias. Give me a bit more to work with if you can.
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