To test for emission, it would seem that the grid voltage would need to
be
zero or even positive to simulate the effect of the peak driving voltage.
If the emission is normal this would cause a very high cathode current,
maybe too high if left for more than a few milliseconds. So, some kind of
pulse test would be safer and less stressful on the tube.
Emission can appear normal until the cathode current reaches a level of
saturation. If this happens at a level too low, then we call that weak
emission. A tube characteristic chart will show these currents and can
be
used to
evaluate cathode emission.
Use of AC on the screen and plate will certainly allow a pulse test of
sorts. You might try the test with no grid voltage and see how that
plays.
The
lower voltage you are using seems a good idea as well.
Also, the AC cycle needs to be in the same phase for both the screen and
plate. Otherwise peak plate voltage will happen when there is reverse
polarity on the screen and visa versa. High positive screen voltage with
no or
reverse plate voltage is not good for the screen as it will try to
accept
all
of the electrons emitted from the cathode and that can be a bunch.
This is a very interesting subject and I hope you test further and let us
know what you discover.
73,
Gerald K5GW
In a message dated 9/27/2010 3:11:23 P.M. Central Daylight Time,
rj3819@yahoo.com writes:
This tube is on ebay ..
Worried about getting an older gassy tube .
The seller states ..
This auction is for One 4-250 / 5D22 Transmitting Tube. The labeling
on
this
tube has been worn other than the tube number that you can see in the
pics. I
am not sure of the manufacturer, but I am quite sure that it is either
Eimac or
Amperex. The visible labeling on the tube reads:
JAN-CIM-5D22
Made In USA
There is a stamp inside the tube also that reads:
Q8-9034.
This tube is tested for emission from a High Voltage Transformer:
460 VAC through a 15K @ 10 watt resistor to screen
920 VAC to plate
6.3VAC @ 8 amps to filament
-40 VDC to grid
This tube tested at 200 MA.
I have no idea about testing and if that is good to determine tube
emission or
not.
I have one already and thought I could have a pair for spare tubes for
my
4-400A amp ? I know .. not exactly the same .. is just plate dissipation
the biggest diff? would Be able to use them as a lower power set of
spare
tubes? or just make another amp with these?
I hope replies go to me as well as the list as the auction will be over
in
4
hours..
Randy - N2CUA
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