Bottom line,... use the specified tubes. Yes RealZap, there are reasons
for that. I could get into a long dissertation on that, and a list of examples
of what has come across our benches. The consequences are that these
amps end up on our benches.
-It has to do with characteristic curves of the tube specs.
-The way Bogner designs the amp sections.
-Spider Valve, Alchemist and the DT series have a digital section for processing,
so these are basically hybrid amps.
-Since these are hybrid amps, you can't get away with the same kind of tube
swapping like we used to do back in the 1960's and 1970's.
-You can't use the same bias on other tubes as you do with the EH's.
-EH's go through more scrutiny.
Consequences are red plating which damages tubes and surrounding circuitry,
blown digital boards and other such failures. Bottom line,... use the specified tubes.
And RealZap,... keep up the good work.