Vajra SE/PP pot

[Maurizio]

Hi all, I was wondering if anyone could help me understand this SE/PP pot that I have seen in the Vajra. I understand that the signal to one of the 2 output valves is gradually switched off, leaving with a pseudo-SE amp. How would this work in a fixed bias amp? I mean, would it affect the biasing of the 2 valves? How would the cathode current change with the pot in an amp say like an Express? And if it changes the bias point of the valves, would it be detrimental to valve life?
Sorry if the questions are daft and thanks in advance for your help.
Maurizio

[VacuumVoodoo]

You answered yourself in the first sentence. Only the signal to one of the power tubes is affected, bias doesn't change whether it's fixed or cathode.

However, for this thing to really work properly the bias on both tubes should be varied towards hotter while the signal to one tube is reduced. This is to keep the tube receiving full signal longer in class A mode of operation.