Speedball Voltage Check Issue [resolved]

[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.