The main thing is we need to figure out what caused R15 to explode. It could be dangerous to use the amp until we figure out what happened. If you are not 100% confident in your solder joints then please take out the board and re-solder them…it’s much better to be safe than dead…or have more components blow up. Also, try tightening your tube socket pins just to make sure everything is making good contact.
All the current the amp uses goes through R15, so something in your amp must have been drawing a lot more current than it’s supposed to. It makes me think that something is shorted….like a bad solder joint or something.
Are you sure that TP6 and TP9 are correct? The bias voltages on those parts of the circuit seem solid, so those test points should be higher. It concerns me that TP5 isn’t giving you a voltage…that’s pretty important to know what that voltage is. Like I said, try tightening your tube sockets, especially pins 8,4, and 9, and re-measure these voltages. Make sure you have the amp plugged into an 8 ohm load (speaker) at all times, even when you take these measurements.
Let me know what you find.
Good luck.
-Brach