[Amps] Protecting the control grid of a tetrode

[2]

>Let me start this over.
>
>Typically it is imperative to not apply drive to a grid driven tetrode 
>unless anode voltage is applied. 

**  In grid driven, Class AB1, there is zero grid current and zero 
grid-dissipation whether anode V is applied or not.  The critical thing 
is that screen V not be applied unless anode V is present.  

> This is usually accomplished by 
>interlocking the T/R switching.
>
>I have a Harris RF-110A which uses a pair of 8122s. When operating, the 
>8122s are Class A.  However there is no protection against applying grid 
>drive at any time (power on / power off / anode on / anode off / filament 
>on / filament off)  - the input is completely unswitched.
>
>Simple question:  Will application of 20 or 30mW of RF damage the tubes 
>when they are not "ready" ??   

**  The rated grid-dissipation is 2w each, so 30mW of drive should be 
safe.  

>It looks like the 8122s can handle a couple 
>watts of grid dissipation each - is this relevant if they are driven when 
>not "ready" ?
>
>I can add a drive interlock if necessary - it's going to be a pain - 
>though not as much pain as toasting the tubes.
>
>Thanks,  Bill
>~~~~~~~~~~~~~~~~
>Bill Coleman    N2BC

-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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