[Amps] Grid Protection Circuit for Titan 425

[Ian White GM3SEK]

Jim Brown wrote:
>On Tue, 20 Nov 2007 09:09:02 -0500, Pete Smith wrote:
>
>>Is this possibly the dreaded power spike that has been discussed from time
>>to time here?
>
>As I read the doc for it, Ian's board offers protection for several faults.
>But the one I am most concerned with is overdriving the grids, which is a
>well known failure mechanism on 3CX800A7 tubes. This can easily happen in the
>heat of battle, as you forget to tune when changing bands or QSYing, or when
>something breaks. More modern amps include such circuitry, but the Titan is
>an older design (late 70's).
>
Have you received my diirect e-mail, Jim? (It was queried by your 
firewall service.)

For an existing amplifier that only needs a few specific improvements, I 
usually recommend the owner to borrow ideas from the circuits in the 
user manuals for my boards. The grid trip circuit will do everything 
possible to prevent major damage from the scenarios that Jim describes.

A more positive method of protection would to compare the band data from 
the transceiver against a similar output from the PA bandswitch, and 
keep the amplifier offline unless the two settings agree. It still 
doesn't fully protect a manual (non-autotuning) amplifier, but at least 
it would make the operator reach across to the amplifier controls.


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek/boards