Tube question
..., Thu Aug 03 2006, 03:18AMI was going to try to make a vttc last night, but I ran into a problem... I couldn't get my tube to do anything. I was givng the filament its rated power, had plenty of b+ (+600v) on the anode, the cathode was grounded, but I couldn't get the tube to draw any current
Am I mistaken in thinking that a triode (or tetrode for that matter) will draw current when you put +voltage on the anode and ground the cathode, until you give the grid a negative voltage which will cause it to stop drawing current?
Re: Tube question
dan, Thu Aug 03 2006, 03:59AM
If you left the grid floating it's probably picking up electrons and thus giving it a negative charge. This would repel the electrons from the cathode and limit the number of electrons getting to the anode. You need to bias the grid to a fraction of b+. If thats not the problem then your tube probably has a bad vacuum.
Edit: w00t my 100th post!
dan, Thu Aug 03 2006, 03:59AM
If you left the grid floating it's probably picking up electrons and thus giving it a negative charge. This would repel the electrons from the cathode and limit the number of electrons getting to the anode. You need to bias the grid to a fraction of b+. If thats not the problem then your tube probably has a bad vacuum.
Edit: w00t my 100th post!
Re: Tube question
Steve Ward, Thu Aug 03 2006, 04:15AM
I think it depends on the type of tube, some of them need a negative bias to turn them off, but i think some also are off with 0V on the grid. Did you leave the grid floating or did you ground it to the cathode? I would think if it was floating, it would act much like a diode.
Steve Ward, Thu Aug 03 2006, 04:15AM
I think it depends on the type of tube, some of them need a negative bias to turn them off, but i think some also are off with 0V on the grid. Did you leave the grid floating or did you ground it to the cathode? I would think if it was floating, it would act much like a diode.
Re: Tube question
Steve Conner, Thu Aug 03 2006, 09:28AM
What you said is correct for a triode. But if it's a tetrode or pentode, it won't do anything unless you connect a few hundred volts to the screen grid too. Not too much though or you might melt the screen and trash the tube.
Steve Conner, Thu Aug 03 2006, 09:28AM
What you said is correct for a triode. But if it's a tetrode or pentode, it won't do anything unless you connect a few hundred volts to the screen grid too. Not too much though or you might melt the screen and trash the tube.
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