I'm glad you discovered the SS diode feeding each of the rectifier anodes trick. I had the same problem with my Sixties B15NF. The diodes increase the PIV of the rectifier system to prevent flashover and blowing of fuses. This was my reason for asking my question. Member @beans-on-toastgave me the tip.
Enjoy your amp.
Back in the late sixties I used a Marshall 4x12 driven by a Leak TL50 Plus and a small single valve preamp I built to control the Leak.. it worked well but the cabinet WAS more than a little awkward to load in and out!
In this day and age, considering the power available from amplifiers, no one should still be using 1/4" phone plugs to connect between amplifier and cabinet. Never ever use an instrument cable for this duty!!
I've been using rack pre-amps since the early eighties when I built my first SS power amp. Since then I've enjoyed a few different units, some of my own build.
My current amp is a 2KW capable Class D stereo power amp. I built a three tube two channel pre-amp to drive it. It has served me well.