The 5AM8 tube is identical to the 6AM8A tube except for heater rating. This tube is primarily used in television receiver applications. It has 3 grids, which makes it a pentode. The diagram shows that the tube actually has two different options for use, as a pentode off the left path, or a diode off the right path. For studying saturation, the path should not make a difference. The usual operating conditions are 6.3 volts across the heater and 125 volts potential difference across the plate. (RCA)
|This is a diagram of the 5AM8 tube.|
In order to produce the saturation current, I used a plate voltage between 0 and 20 volts again, and a heater voltage of 3.09 volts to start with. 3.09 volts potential across the heater produced the graph shown here. With that heater temperature the maximum current appears to be around 2 milli-Amps. When I tried the same tube with a hotter cathode, the effect takes place at a greater maximum current level. For the trial where the heater was run with a 3.8 volt potential the maximum current was close to 12 milli-Amps, and when the heater was raised to 4.4 volts the maximum current went up to around 17 milli-Amps. This is of course what I expected, since a hotter cathode will be able to release more electrons and support a higher current level.
These are plots of the current produced as described above. The filament voltages are noted in the titles. In the graphs you can see that as the fillament voltage increases, the maximum current increases as well, as more electrons are pulled off of the cathode.
Saturation on the 6X4 tube
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