[Amps] Tetrode tuneup

[TexasRF@aol.com]

Hi Bill, if by "floating the screens" you mean no voltage applied and no  
path to the cathode, then this is not a good thing! The screen voltage will very  
quickly rise to the plate potential and with no grid bias, the plate current  
will jump to a very high value. The result will be a very sudden and loud  
"KAPOW". To prevent this a current path between the screen and cathode has  to 
be present. I have not used this tube so not sure what the resistance value  
should be but probably several K ohms.
 
73,
Gerald K5GW
 
 In a message dated 3/14/2005 3:09:52 P.M. Central Standard Time,  
n2bc at stny.rr.com writes:

Adding a  "tune" mode to an AM RF PA with a pair of 4-400s.   What's  
better...  floating the screens or grounding the screens.  Does  it matter?

To round out the picture:  no bias supply (grid leak  bias only),  screen E 
derived via dropping R from plate B+

I  have a relay that will easily handle the screen voltage and plan to switch 
 
in a suitable R in place of the screens to keep the voltage coming into  the 
RF deck near normal screen value. I don't foresee it ever being 'hot  
switched' - It probably wouldn't last too many cycles at 3KV.  I  don't want 
to mess with a clamp tube.

THX & 73,  Bill   N2BC  


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