[AMPS] Heath SB-230

[w8jitom@postoffice.worldnet.att.net]

> From:          Rich Measures <measures@vc.net>
> Date:          Tue, 2 Sep 97 21:00:45 +0000

> >1.) It has no grid protection circuit, making it possible to easily 
> >overdrive and damage the grid.

> Over-drive is most likely to strip the oxide coating from the cathode.  
> [see photo in "Parasitics Revisited" (9/90 - 10/90 QST)    All of the 
> 8873/4/5 grid damage that I have looked at under the microscope has been 
> due to the gold plating on the grid boiling away.  Gold boils at 2966 
> degrees C.  The idea of being able to raise the grid to such an extreme 
> temperature with over-drive is amusing. ........ 

The claim it is a "parasitic" is sad, not amusing.

The grid dissipation is FIVE watts. Rated grid dissipation is reached 
at about 60 mA of grid current in the SB-230.

Since the grid heating is caused by kinetic heating of the grids 
outer layer by electrons, and gold melts at a lower temperature than 
the tungsten base material, the soft gold goes first.

Anyone in their right mind would know a 100 watt exciter could easily 
cook a five watt grid if the PA is underloaded. Anyone doubting that 
should ask Eimac, and not take any strangers word...especially if 
that stranger sells "magic cures".

73, Tom W8JI

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