left channel dies after 5 minutes

[Paul Birkeland]

I'm not getting a voltage reading at terminal 2. How long should I wait?

There should be a number on your meter, what is it?

How about the voltages at 21, 15, and 13? Where are you grounding your meter?  Is the solder joint where the black wires meet on the headphone jack nice and solid?

[denti alligator]

T2: 0.002

T13: 0.005

T15: 88

T21: 178.2

Black is attached to the ground right at the power input.

[Paul Birkeland]

Yeah, you have a short.  Can you post some build photos?  Having the TIP50's installed improperly will give this same issue, but not when the 6080 is removed.

[denti alligator]

Here are some pictures. Let me know if there's anything you need to see close-up, or if there's anything I should check.

[Paul Birkeland]

Lift the connection between the big Speedball PCB and terminal 2, then recheck those high voltage terminals (with 12AU7 installed).

[denti alligator]

T21: 238.5

T13:  232.7

T15: 235.8

[Paul Birkeland]

Hmm, now we are getting somewhere.   What voltages do you see at terminals 1 and 5 under these circumstances?

[denti alligator]

T1: 230

T5: 76

[Paul Birkeland]

Well, there's a fault on your big speedball PC board.  You can order up a replacement, or take a lot of very detailed photos of the board out of the amp and perhaps we can spot the problem.

-PB

[denti alligator]

Thanks. Will these help?

[denti alligator]

Any chance to troubleshoot the board as is?

[Paul Birkeland]

I would replace the whole board.  The only connection from the high voltage DC to that board goes through some high impedance resistors to the LED's, then to ground.  Having the high voltage section short out is almost always an issue of proper mounting of the TIP50 transistors, which can be confirmed by pulling the 6080 tube and observing that the problem goes away. 

In your case, that doesn't happen.  That leaves us with a wiring or component installation mistake that has never been made before in the history of the Speedball, or potentially the wiring of the 8 pin socket is such that the original build would've produced the same problem.  There's also the potential problem that the base guiding pin has broken off of your 6080 and it isn't being properly inserted, which is creating the short.

Sending the amp in for repair is also another option in this scenario.

[denti alligator]

Thanks, will do. Any advice on what to do once I've installed the new board? Should I fire it up right away or test voltage without the 6080 in first?

[Paul Birkeland]

You could test without the 6080 to see if the B+ is still being dragged down.

[denti alligator]

OK, new board installed. I'm still getting strange voltages.

1: 174.5
2: 181.1
3: 0
4: 181.1
5: 77.4

6: moves about 0.02 or so (not steady)
7: 171.8
9: 89.6
10: 0.02 (unsteady)

12: 0
13: 180.5
14: 0
15: 203

18: 90.5
19: 91.1
20: 0
21: 218.6

A1: 77.2
A2: 0
A3: 1.575
A4: 0
A5: 0
A6: 173
A7: 14.23
A8: 0

B1: 172.6
B2: 181.1
B3: 172.1
B4: 77.1
B5: 181.1
B6: 89.5
B7: 0.015

main board
B+: 180.7
O: 171.7

left small board:
O: 192.7
I: 200.6

right small board:
O; 77.2
I: 200.6

Note: I did install the silver, round transistors with only about a millimeter gap from the board. I know I should I have given them more. Hope this isn't a source of the problem.