[Amps] AL-80B "Optional" Grid Protection circuitry - identify?

[R.Measures]

The only grid protection that seems to protect a  3-500Z reliably is a 
fusable element --such as a 0.5A, 3AG fuse or a 20 - 39 ohm 1/4 or 1/2 
watt carbon-film R.  While transistor-type protection circuits look 
good on paper, they tend to fail C-E shorted when presented with the 10 
or so ampere spike in grid current during a parasitic event at 95 - 
120MHz.  .  .  Sometimes mo' simple is mo' betta.

On Jan 17, 2005, at 4:48 PM, Charlie wrote:

> The AL-80B manual and web site discuss an "optional' grid protection 
> board I believe they call it. I am the new owner of a used AL-80B and 
> would like to know how I can check if this "optional ' grid protection 
> is in place or not. As best I can tell this amp was new in 1997.
>
> I have several photos of the inside on my site listed below. If anyone 
> can spot it or tell me what to look for I would be very appreciative. 
> I got on this matter after the amp kicked off a couple times on 40M 
> phone.  After several moments it was OK again. I am guessing it was 
> this optional circuit. TY  73
>
> Charlie
> Ham Radio - AD5TH
> www.ad5th.com
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org