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Date: Mon, 27 May 2002 10:11:54 +0200
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Decca component
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>The dead Tx unit still works but not very well. A component across one of
>the transistors burnt out. I have a diagram but do not recognise the symbol
>(perhaps a temperature variable resistor?). It is called R31V and the symbol
>looks like a preset potentiometer, but it looks just like a red disc ceramic
>capacitor.

Hi Mike,

it's most likely a varistor. These components have a very high resistance 
that sinks rapidly once a certain voltage is exceeded.
They are often used to avoid overvoltage (spikes etc...) over 
semiconductors. The important thing you need to know is the breakdown 
voltage of the varistor. Typical this is about 70 .. 90% of the max. 
allowed voltage over the semiconductor, but in rugged equipement (as the 
decca units) it might be less (50% or so) to be on the save site.

73, Rik  ON7YD