help needed: strange voltage readings

FS · 2873

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Offline FS

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on: January 31, 2011, 04:57:30 AM
Hello,
I am new here, and I am a newbie to DIY audio as well...:-)))
I am turning to you guys for help with my Crack build. The resistance check of the circuit was OK. When I put in the tubes and switched it on, only the 6080 would glow, the 12AU7 would not. My first assumption was that maybe the tube does not have to show a visible glow. Therefore, I proceeded to the voltage checks and got the following voltages:

Terminal   Voltage expected   Voltage measured
1               90                               0
2               170                             0
3               0                                0
4               170                             0
5               90                               0
6               0                                0
7               100                             53
8               0                                0
9               100                             55
10             0                                0
11             0                                0
12             0                                0
13             170                             155
14             0                                0
15             185                             166
20             0                                0
21             206                             175

A1             90                               0
A2             0                                0
A3             1.5                              0.14
A4             0                                0
A5             0                                0
A6             90                               0
A7             0                                0
A8             1.5                              0.14
A9             0                                0

B1             90                               0
B2             170                             137
B3             100                             55
B4             90                               0.1 - 0.3 (fluctuating)
B5             170                             157
B6             100                             56
B7             0                                0
B8             0                                0

I would appreciate any help with this as I have re-checked all wires and they seem OK to me. Should the 12AU7 exhibit a noticeable glow? Could that tube be broken?
Thanks very much in advance.
Falko



Offline Grainger49

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Reply #1 on: January 31, 2011, 06:01:58 AM
Falko,

You have a PM to keep me from embarrissing myself on an amp I don't have the schematic for.

12AU7s don't glow much.  Try a dark room.

Your incoming B+ (high voltage) on the 6080 is low.  It is nonexistent on the 12AU7.

More later, less sooner.



Offline FS

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Reply #2 on: February 03, 2011, 12:12:50 PM
Hello Crack-aficionados,
I would like to close this thread as my headphone amp is working now, thanks to the great help that I received from Grainger, one of the tireless and selfless volunteer support specialists in this forum...:-)))
And I just wanted to repeat my sincere thanks to Grainger for the immediate response to my question and all the help with troubleshooting my Crack build.
His willingness to help and to share his expertise made this a really easy ride for me...Thanks also to the Bottlehead team for the nice kit, which was spot on for a DIY newbie...:-)))
Now I am off to more listening....
Have a great evening!
Falko