Jadis JA 50s power tubes

I contacted Jadis in France regarding the possibility of using KT-120 power tubes for my JA 50s. I received a response from Patrick Calmettes saying only KT-90s should be used in the amps due to high voltages. However, my amps have been using EH KT-88s, which they were supplied with upon purchasing them used from a very knowledgeable Jadis technician in NY. The amps are self-biasing....anyone have any experience using these amps?