[Amps] 4-250A testing

[TexasRF at aol.com]

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 at 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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