@jslateiv the gain adjustment is only possible on the 300b something I wish Mick had informed me about before I decided to buy, buyers should be made adware of that I feel.
I am certain it is the switch that is the problem, but unfortunately I live in the North Atlantic Ocean with no real tube experience person to help me with this problem, really don’t want to send the pre back to Mick one more time.
it’s unfortunate as I feel only half of the amp works as intended, but I paid full price.
Anyway, the sound from the 6SN7 is great, even if I have to use 12db attenuators
to match better with my power amp.