[Techman]

As regards the valve mismatch, I have to admit that the results are a bit confusing. Badly out of match valves will certainly cause some hum, but I now think that some of the problem is with that failed reservoir capacitor - you've been a bit unlucky with that, as I said, Keep feeling them for any signs of heating up. I've found that when these particular valves are far enough out to be causing the non-cancellation of hum, it's usually down to the heater of one of them not working to full potential, but you've visually checked and shown a picture of the heaters glowing and they looked the same. I would advise checking them again, just remove the rectifier valve so that there's no HT to blow up that faulty capacitor. You could measure the heater current on each one, but that's getting a bit complicated, although it may come to that in the end.