[Amps] 4CX1000A

[Ron Youvan]

   Carl KM1H wrote:

>> I'm not mike, but I think the reverse screen current is not strictly normal, in a perfectly built
>> tube you should see none.
>> These tube are built with the screen grid components hiding in the electron shadow of the control
>> grid elements. When the alignment isn't perfect the electron beam strafes the side of the G2
>> elements which produces emission via secondary emission.
>> I suspect most new good tubes of this kind show negotiable emission. Those that do emit
>> significantly may find their way onto the hands of HAMS more easily.


> I suggest reading page 4 and 5 in the below link.
> http://www.g8wrb.org/data/Eimac/4CX1000A.pdf

> And then tell me its not perfectly normal. Most external anode tetrodes I'm familiar from the 4X150A
> to 4CX1500B can exhibit negative screen current.

   I stand by my statement, "in a perfectly built tube you should see none" and "is not strictly normal"
You say: "Most external anode tetrodes I'm familiar from the 4X150A to 4CX1500B can exhibit negative 
screen current."

   I agree, "Most" and "can exhibit" but not in 100% of them, in a beam power tetrode or pentode the 
screen grid is supposed to be in the shadow of the control grid and when it is not completely out of 
the stream the electron beam strafes the screen grid a glancing blow, the is prime angle to create 
secondary emission, which is the reverse screen grid current.  (emission)
I have worked with many RCA (now Burle) (like 4CX5000R) and Thomson beam power tetrodes (like 
TH-331) that did not exhibit any noticeable screen emission.
   I am sure lining up the screen "cage" with the grid "cage" properly, is the hardest part if 
constructing this kind of tube.  (to make as many as possible that work well)
-- 
    Ron  KA4INM - Did you know ...
                  ... that no-one ever reads these things?