I've really enjoyed playing the Champ Micro for the last several weeks. It's a sweet practice amp. But I'd been bummed that I was getting a fairly strong hum when powered up, even without any input. I saw on this thread that a solution to the problem is to add an additional filter cap and that @robrob has changed the schematic for the Deluxe Micro accordingly. So I bought a JJ 50+50 uF at 500V can capacitor. This morning I disconnected the original 47 uF. You can see it sticking up in the photo but it is completely out of the circuit, and I clipped in the new 50+50. I followed the Deluxe Micro schematic for this since it is very similar, at this point, to the Champ. The good news is that it works! I'm happy to say that the hum is hugely reduced. I wouldn't say it's "dead quiet" but it is nothing to worry about anymore. The resistor between what is now B and B+1 was measured to be 462 ohms. New voltages: B: 395V B+1: 386V (used to be 399V) B+2: 275V (used to be 279V) Now I just have to figure out where I'm going to mount the can cap, solder up the connections, and put it all back together.