I've got a late 1960's amp designed to run 7027A's and it runs very high plate voltages to get 75-80W. I've seen a scan of a fax of a photocopy of the circuit diagram and there is a handwritten indication that the plate voltage when new was 575V. Measured recently my amp was 623V. Modern 7027A's are 6L6's in disguise and 623V is way above max. spec. for any modern 6L6 I've seen. Short of rewinding the OT, is there any other way to reduce the plate voltage? Currently it is running a pair of JJ 7027A's that I fitted this year and it is running quite happily, although I have only been using it at low volumes at home at the moment.