You are thinking of the old 444 solid state amp. The 411 Centaur uses 3x 811A
tubes. TT states on their website that they can no longer repair the 444.
Concerning the history of the 422..the original model had Eimac 3-500Zs and the
tubes were biased "On" even in standby. TT later offered a mod to change the
bias circuit and added this to later versions. I have done this to a friends
422 along with new black panels/case to match the Orion.
Just sold my 422 to make way for more Elecraft equipment, great amp. Know where
a 422 is with Eimac's in the local Colorado Springs area that is for sale.
Also have an L-4B with the original tubes, still get full power and another
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