Speedball Voltage Check Issue [resolved]

[Paul Birkeland]

I would pull the Speedball and put the resistors back. There's an issue with the underlying build that needs to be resolved first.

[M42]

I reinstalled the two resistors. I could not find the identical value (22.1 kohm), I've used NTE 1/2 watt 22 k ohm, 2% in their place.

Resistance:                                        Voltages:

1     .378 m ohms                               91.5                     
2     .342 m ohms                               229
3     0                                                0
4     .329 m ohms                               228
5     1.06                                            26
6     2500                                           0
7     3050                                           26
8     0                                                 26
9     2.95                                            0
10    2508                                          0
11    n/a                                            0                                         
12   0                                                0
13   .635 m ohms                               0
14   0                                                0
15   n/a                                             233
20   0                                                0
21    n/a                                            238
22   01.5                                           a1   26                                     b1    90.6
b3   2950                                          a2    0                                      b2    230
b6   2953                                          a3    1.45                                 b3    26
rca ground jacks:                               a4    0                                      b4   26
ground lug    0                                   a5    0                                      b5   230
center pin     2502                              a6    90.7                                 b6   0
                                                         a7    0                                      b7   0
                                                         a8    1.56                                 b8   0
                                                         a9    0

[Paul Birkeland]

5     1.06                                           

The amp should not be powered on again until we can determine what went wrong here.  Your last resistance reading was 3,000 Ohms, now it's 1 Ohm.  Neither resistance reading is correct.

I would be interested in seeing more photos of the build, as I might be able to spot the issue.

-PB

[M42]

Thanks Paul...I'll put some up this evening.

[M42]

A few more photos of the amp...

[Paul Birkeland]

Pull the 6080 and power up the amp with just the 12AU7, then measure the voltages at 1 and 5 again.

-PB

[M42]

Measured once more before pulling the 6080 tube:

led still out on 9 pin socket
terminal 1   92.4v
terminal 5   26.8v

6080 removed:

both led's lit on socket
t1   92v
t5   94.6

replaced 6080:

both led's lit
t1   78v
t5   80.5v

removed 6080:

both led's lit
t1   92.6v
t5   95.4v

6080 in:

both led's lit
t1   78v
t5   81v

I had the big tube out of the amp prior to this issue, but am certain it was correctly seated/oriented at the time of the voltage checks for the small board. It would appear I can reinstall the small board?   

[Paul Birkeland]

If your keyway has broken off the 6080, and the tube was inserted off by just one pin's worth of rotation, that would explain 100% of the issues that you're having.

-PB

[M42]

I do have an index mark on the tube, but despite that I must have reinstalled the tube incorrectly??? This appears to be the only logical explanation...a humbling lesson to be sure. I installed the large board without incident. Voltages measure:

OA  103.9V
OB  101.6V
G    OV
B+  174.5V

The 6080 tube now appears to be microphonic...I have ordered replacement tubes. I've had little time to listen to the amp, but I'm very happy with what I hear so far! Thanks very much for your help with this.

[Tom-s]

Leave Crack on for a while (a day continuous), might get rid of the microphonics.

[M42]

Thanks Tom, I'll give that a try.