Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: monona1 on January 01, 2014, 01:37:20 PM
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So I'm working on my first build -- the crack kit and I discovered a problem during the voltage check. A number of terminals are reading high. Specifically:
Terminal Expected V Measured V
1 75-90 140
7 100 140
9 100 140
A1 90 145
A6 90 140
B1 90 145
B3 100 140
B4 90 140
B6 100 140
Also the LED's are not coming on.
I've triple checked all connections and resoldered any connection that looked questionable and a few more just for good measure. The LED's are oriented correctly (silver band toward center post) and I have verified that the LED's do work by lighting them up with my multimeter set on ohms.
Both vacuum tubes are glowing as they should. I pulled out and reinserted each tube approximately 10 times in case there was a bit of corrosion on a pin preventing a good connection. I wouldn't think it would matter, but in case it does - before the build I broke the stock 12au7 tube so I replaced it with a JJ electronics brand 12au7.
Any advice would be most welcomed.
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Thanks!
ps I have photos to upload, but can't figure out how to attach them?
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Do you have the wire from the center post of the nine pin socket to the terminal 3L connected? And is that terminal making good contact where it is screwed to the chassis plate, like no paint or powder coat in the way?
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Yes, that wire is attached.
Also I have continuity from the center post of the 9 pin socket to terminal 3. And the connection from terminal 3 to ground seems to be ok because I have continuity from the center post to the chassis plate.
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You can upload the photos by hitting the "+" that says "Attachments and other options" next to it. You could also host them at a site like imageshack.
Your voltages suggest that nothing is drawing any current, I think the issue will probably pop right out from the photos.
-PB
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here are the photos
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Nicely done. Nothing jumps out at me in the pics. Can we see a close up of the 12au7? Maybe there is something wrong there.
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this is the jj electronic 12au7 i'm using
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I can't quite see in the photo, but are the two lugs of the volume pot that have black wires going to them connected together?
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I can't quite tell from the photo, but does it say ECC83? That's not right. A 12AU7 is an ECC82. ECC83 is a 12AX7, which would glow but not draw enough current. Is that the tube we supplied?
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Zooming in, it does read ecc83...Try the stock 12au7
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Bingo that's probably it!
The original 12AU7 broke when i was taking everything out of the packaging. I bought a new 12AU7 through amazon. I received a box that said 12AU7/ECC82 - however i didn't notice that the print on the actual tube says ECC83S. Apparently the tube was mispackaged.
I should have the correct tube in a few days :)
I'm highly appreciative of the sharp eyes and attention to detail that found this. Thanks Doc B and Ashneel.
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Old Doc isn't quite ready to be put out to pasture regarding tech support. A lesson for you boys here in the lab. ;^)>
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quick update: I got the right tube in and the amp is working great now :)