[AMPS] tube compatability

[w8jitom@postoffice.worldnet.att.net]

Hi Bob,

> My copy of Bill Orr's Radio Handbook shows one version of a grid 
> over-current protection circuit designed, as I recall, by W8ZR.  
> Some years ago, a fellow (might have been ZR) was selling printed-circuit
> boards for his own flavor of circuit.  
 
> What's the latest wisdom on creating a suitable circuit?  Any source
> of PC boards or other short cuts to getting the job done?

You might contact Ten Tec and see what they did to the later units.

Otherwise, Ameritron can sell a timer-overload board that is easily 
modified for any rig. It responds within a few milliseconds of the 
overload, much faster than you can see a meter move.

When I was testing a PA with 3CX800's, I had no overload system 
installed. I had a few "woops" that lasted only long enough to see 
the grid meter get near the pin for a few brief instants. I ruined a 
new pair of 3CX800's in one day, after about five hits on the grids 
with a few hundred ma for a very brief period. When I cut open the 
tubes, they had gold "melt balls". 

Adding the overload circuit is a must with any low dissipation grid, 
since a 100 watt exciter can easily and  quickly trash a "few watt 
rated grid".



73, Tom W8JI

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