Crack+Speedball Voltage issues + smoke [SOLVED]

[Codeine]

I received the parts today. I soldered in the missing LED on the big board. Before installing the big board I checked the mounting of the TIP50s. To my surprise, the metal contact on one of the TIP50s was shorted to the heatsink and therefore shorted to ground! I desoldered it and took it apart. The plastic lock washer was melted around its shoulder. I straightened it so it could hold the screw without letting it come in contact with the heatsink. I threw in a new TIP50 and put them all together but without the flat washer to let the lock washer's shoulder completely secure the screw. I hooked it up and the voltages all checked out. This might explain the spark on the first run. The 270 Ohm resistors still get very hot and the heatsinks too. Any ideas on how to make the mounting more reliable around that part? Because the washer might melt again after long use and short the metal side to ground.

The amp runs great with my optical Modi. No hissing or noise so far

Edit: I also got a 10W 270 Ohm wirewound resistor to replace the long 5W resistor later.

[Paul Birkeland]

The shoulder washer on the TIP50 would melt from the short, not from general operation.  We can pop a replacement in the mail if you'd like, as that part is quite important. 

[Codeine]

Ok, so I did some modification to the TIP50 mounting, and I think it'll work fine. So I replaced the screw with a Nylon screw and a nylon flat washer in the back with a nut. Also replaced the 270 ohm resistors. Put in a 10W as the long one and a 7W as the other one. They run cooler now I think (at least the 10W resistor). Also did a temp measurement:

10W 270 Ohm (longer one) = 55 C
7W 270 Ohm = 95 C
6080 Tube = 104 C
12AU7 Tube = 60 C
 

[Paul Birkeland]

I would be a little concerned about the long leads on that 10W resistor.

Also, were you able to get enough tension on the nylon screw?  If the TIP-50 isn't tight against the heatsink, it will overheat. 

-PB

[Codeine]

I'm planning to cover the leads with some heat-shrink wire covers. I used an 8-32 screw which turned out to be a tad bit wide for the heatsink hole, so I had to "screw" it in with a little force. Overall, with no room to play and the nut pulling it on the other side, it pushes the transistor very tightly against the heatsink.