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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I 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?
Registered Member #223
Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125
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.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
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.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
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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Tube question
