[AMPS] Re: Parasitics

[Jon Ogden]

>Nonsense Rich. You only "claim" the bandswitch was damaged by VHF. 
>You have nothing more than a guess or personal opinion what happened.
>
>In a less than 360 degree conduction angle PA, if plate load 
>impedance is raised with a high Q tank, the anode and tank voltage 
>can soar.
>
>The peak anode voltage can swing below the zero rail of the 
>chassis (negative), as well as greatly exceed twice the dc HV.


This anode and tank voltage is obviously the voltage of the HF signal.  
And it is an AC signal, not the DC like the anode supply.

>
>It is possible, by unloading a tank in a conventional PA, to generate 
>voltages of many times normal operating voltages. Underloading of a 
>tank is the single largest cause of tank circuit arcs, and is a 
>repeatable and measurable cause source of damage.

If the HF tank voltage can vary wildly and do what you say, which I 
belive it can, what would prevent the VHF voltages in an oscillatory 
condition from doing the same thing?

If the tube has gain at VHF (which it does, we are all in agreement on 
that) then what would prevent the tube from generating voltages high 
enough to arc or discharge across the bandswitch in a runaway oscillation?

Why is it possible at HF and not at VHF?

To me, it doesn't make sense to claim that in one operating frequency 
region an amp will do one thing, yet in another region where it can 
easily operate, it will do something completely different.

Please explain why HF energy can cause arcs and huge voltages while VHF 
energy cannot?

I am ignoring the presense of the VHF parasitic suppressor.  I am 
assuming that it is either not working properly or is blown.  IMHO, a 
properly constructed supressor will effectively limit that VHF voltage.

Thanks!

Jon
KE9NA





-------------------------------------
Jon Ogden
KE9NA

http://www.qsl.net/ke9na


"A life lived in fear is a life half lived."


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