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Banned on 1/22/2011 for repeated rule violations after multiple warnings. Registered Member #3299
Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
So say you have a tube has a filament voltage of 6.3 volts, you power the filament up, put one probe of a multimeter on one filament pin, and the other probe on the pin for the grid and the multimeter reads about 3.3 volts, does that mean there is a grid to filament short?
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
It's probably some amount of current generated by the grid picking up the electrons ejected by the cathode and collected by the grid. To check if there's a short, remove the tube and measure between all the elements. You should see no connections between them (unless... of course, there's an intentional connection shown in the datasheet). To test if the tube is good, set it up like it's supposed to be and see how closely the transfer characteristics match the datasheet.
Banned on 1/22/2011 for repeated rule violations after multiple warnings. Registered Member #3299
Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
the tube is an 811a remake, i checked this with nothing else wired up, it never worked on my vttc
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
Take the tube in your hand and measure for a short between the filament pins. You should see one.
Now, measure for a short between one of the filament pins and the HV pin. It should not read a short. Now, measure for a short between a filament pin and the grid. Again, there should not be a short.
Of course, the best test is to see if it works. You could also build a tube tester
If you want to get more technical: 1. Connect your DC filament voltage 2. Connect your DC HV to the plate-filament. Have a DC current meter set to read the current going through the plate. As you increase the plate voltage the current will go up.
3. Now you can test the grid. If you have a negative DC voltage source, connect it to the grid-filament (filament is ground for the plate and grid). As you apply more negative voltage the plate current will go down.
Don't worry about testing the transconductance at this point.
The tester I am referencing on Youtube works closely to this description.
Banned on 1/22/2011 for repeated rule violations after multiple warnings. Registered Member #3299
Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
what is a simple circuit a can build with an 811a, maybe drawing arcs with it, apply -dc to the grid and if it doesn't arc its, tube in series with mot.
Banned on 1/22/2011 for repeated rule violations after multiple warnings. Registered Member #3299
Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
I think i'm gonna screw the whole 811a tube idea and go with this
Banned on 1/22/2011 for repeated rule violations after multiple warnings. Registered Member #3299
Joined: Sat Oct 09 2010, 08:11PM
Location: Bantown, USA
Posts: 220
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