These are not the analog tube amps from the 1960's and 70's, where you can swap between tube types.
This is a hybrid amp with digital and analog sections.
"YOU CAN USE THE 6CA7 TUBES IN A DT50 I AM USING 2 MESA 12AX7 TUBES AND 2 JJ 6CA7 TUBES AND IS RUNNING FINE"---
I might be now, but I see way too many DT50's come across my bench just for that reason. Incorrect tubes and incorrect bias levels, I see this way too much. It will damage something eventually, running it like that. Do not use Mesa, JJ, Ruby Tubes or Groove Tubes in this amp.
The characteristic curves between these tubes may be close, but not close enough.
These are Bogner hot rods, don't hot rod the hot rod or something will fail.
The characteristic curves are not close enough, and using the specified bias on these other tubes would be the wrong bias.
I see way too many DT50's come across my bench just for that reason. I'm trying to keep that from occurring. Please don't do that.
For those who say that EH's are just Sovteks with EH painted on it,... EH owns the Sovtek factory.
The EH labeled tubes go through extra scrutiny.
Use the specified Electro-Harmonix 12AX7's and EL34's. For those who ask soft, medium or hard,...
... I'm told by an EH person that we get the mediums.