I think you found your problem , once you fix your PT in a secure and permanent way, I bet you'll find your 240V or so volts between the 80's filament and chassis and, important thing, you'll find the negative voltage generated across the 235 ohm will be quite less than your -31.6V, it should be roughly -17V.
With that dead short, no wonder you heard a pop/arc!
Ok also about the 5.25V on the rectifier's filament, much much better!
Best regards
Giulio