newbie needs help
- Thread starter bmurph7
- Start date
After a long delay due to work, I finally got the parts I needed and reassembled my Crack. Testing was good in Ohms tests, and good for voltage until clumsy me shorted an LED. I replaced it, but I dropped the 6080 tube from chair height onto carpet. Now on terminals where I should get 170v, I get 202v, at terminal 7 I get 0v instead of 100v, and at B3 I get 0v instead of 100. All the voltages that should read 170v are at 202v, #9 is 125v s/b 100v, #15 is 217v s/b 185, #21 is 230v s/b 206. Did I break the tube? Or could something else be wrong. I didn't get a chance to check the B voltages before I shorted the LED and subsequently dropped the tube, but #2, #4, #7, #9, #13, #15, and #21 all had correct readings.
As always, I would appreciate any help I could get.
Thanks
Brent
As always, I would appreciate any help I could get.
Thanks
Brent
Hello Brent,
If terminals 1-5 read the correct voltages, then you can be certain that the 12AU7 is functioning correctly.
7 and B3 are tied together, and 0V there indicates that this half of the 6080 isn't drawing current (9/B7 is the other half, which is operating appropriately).
What I would check is to ensure that there is voltage on B1, it should be the same as terminal 2, and voltage on B2 (which is nearly mandatory). Next, measure the resistance from ground to B3 to be sure the cathode resistor is in properly, being aware that you might have to pop the 100uF coupling cap out. Since you haven't mentioned so, I'm assuming you don't have the Speedball.
If all these checks pass, then the 6080 may have been damaged, but this is a super tough tube, so it seems unlikely.
-PB
If terminals 1-5 read the correct voltages, then you can be certain that the 12AU7 is functioning correctly.
7 and B3 are tied together, and 0V there indicates that this half of the 6080 isn't drawing current (9/B7 is the other half, which is operating appropriately).
What I would check is to ensure that there is voltage on B1, it should be the same as terminal 2, and voltage on B2 (which is nearly mandatory). Next, measure the resistance from ground to B3 to be sure the cathode resistor is in properly, being aware that you might have to pop the 100uF coupling cap out. Since you haven't mentioned so, I'm assuming you don't have the Speedball.
If all these checks pass, then the 6080 may have been damaged, but this is a super tough tube, so it seems unlikely.
-PB
PB
Thanks for your help. B1 voltage is 90v, which the manual call for. B2 is 203v. The manual calls for 170. The resistence at B3 is 2.9k ohms, which the manual also calls for. I did not remove the cap. Since it checks OK according to the manual, I wasn't sure I needed to remove the cap. Is there a way to check the tube?
Thanks
Brent
Thanks for your help. B1 voltage is 90v, which the manual call for. B2 is 203v. The manual calls for 170. The resistence at B3 is 2.9k ohms, which the manual also calls for. I did not remove the cap. Since it checks OK according to the manual, I wasn't sure I needed to remove the cap. Is there a way to check the tube?
Thanks
Brent
bmurph7 said:
Well, you could look around for somebody with a tube tester, but you have verified the correct bias voltage, that there is plate voltage, and that the resistor is properly connected and not shorted, so in a way you have tested your 6080.
I'd snag another one and you should be back in business.
-Paul
Sweet success! Bought a new tube and everything is good. Amp sounds great! Thanks to everyone for all the help. I learned a lot, and am looking forward to my next project.
This was my first time for something like this, and I was amazed at all the help I received. Again, I can't thank everyone enough!
Brent
This was my first time for something like this, and I was amazed at all the help I received. Again, I can't thank everyone enough!
Brent
