Quote:Rectifier is fine but also flashed before regulator went off.
The regulator needs both high voltage and a load to light up. When a rectifier tube shorts (the flash) there is no longer any high voltage so consequently the regulator tube won't stay lit.
A common mistake is to think that a rectifier is good when the heaters are still working. Most shorts happen in the high voltage plates of the tube which will always take out the internal fuses usually instead of or in addition to the mains fuse.
Sometimes the fuse board itself shorts in pre 2019 models when the rectifier arcs which results in the board sacrificing itself instead of the rectifier. This has only happened 3 or 4 times in the past two years so it is not common, just possible.
Most likely just get yourself some new fuses and a new rectifier tube and you'll be fine. Rectifiers can arc without actually failing, but the arc can blow a fuse. When you try the rectifier in a different amp it seems to work fine.
Anyone having even a small arc in a rectifier tube should immediately order themselves a New Old Stock 5U4G as a replacement. That will end the whole pre-mature rectifier tube failing problem and make your life less stressful, not to mention have the bonus of improving the sound by as much as 20%. A New Old Stock Rectifier tube should last easily 5000 hours and often well surpass that figure in these amps.
Steve