[AMPS] one side of heater to ground...

[2]

>
>-
>While constructing 80 & 170Mhz triode amplifiers 
>for a research project (some time back), I had 
>reason to contact Bill Orr with questions. One of 
>said questions was to ask why one must tie the 
>heater and the cathode of the 3cx400a7 triode to 
>one side of the heater.  From memory, this was 
>suggested in a data sheet I had at the time. 
>-
>Other than "smart practice," he wasn't able to give me a 
>concrete reason. Memory of that moment has been in 
>my noodle for some years.  
>-
Dispite the fact that Mr. Orr was well liked, he seemed to lack a 
concrete understanding of RF amplifiers.  Terry Gaiser, W6RU apparently 
came to the same conclusion after a number of conversations with him.

>I made the amplifiers (of which I still have right here) 
>trying both the separate and tied heater - cathode 
>combinations.  
>-
>I used common Omite chokes and some home brew 
>chokes in the circuits. Both amplifiers did their tasks 
>and are now in standby storage.  
>-
>I didn't notice much operational difference using 
>the heater/cathode connection combinations.  

The difference is when there is a HV arc to gnd.  ,  

>Might 
>be the power level I was working with, the type of 
>tubes or I just got lucky.  So why is it a common 
>must-do to tie a side of the heater and cathode as 
>one in some types of tubes..?   

To prevent breakdown of the cathode-heater insulation during a major 
glitch.

>...

-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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