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[AMPS] Zener screen supplies

To: <>
Subject: [AMPS] Zener screen supplies
From: (Steve Thompson)
Date: Sat, 14 Apr 2001 09:13:44 +0100

-----Original Message-----
From: measures <>
To: Ian White, G3SEK <>; AMPS <>
To: <>
Date: 14 April 2001 03:39
Subject: Re: [AMPS] Zener screen supplies
big snip

>>There's nothing inherently wrong with current limiting, or any other
>>design features. They can all be made to work.
>With a zener-string screen regulator, operated through a high resistance
>from the anode supply current limiting is automatic.

A clarification - my original comment about current limiting referred to the
sinking capacity of a shunt regulator, so that the regulator didn't have to
handle arc current, and the screen meter got protected.


>> The foolishness is in
>>*assuming* anything, when we should be *designing* everything!
>>Everything needs to be designed twice over, once for normal operation
>>and again for a range of fault conditions.
>>Good flashover protection for the screen requires at least four separate
>>design features:
>>1. B+ surge resistor to limit the maximum possible current. This gives
>>you a basis to design the rest of the protection features.
>>2. Something to protect the screen itself (and the bypass capacitor)
>Why protect the screen in a bad tube?
>>against overvoltages when the flashover connects the screen to the
>>3. Protection for the screen supply against (a) the overvoltage coming
>>back from the screen, and (b) any actions that screen protection circuit
>>takes (eg applying a short to ground).
>>4. Shutdown circuits (fuses, breakers etc) to impose a cutoff on the
>>whole scenario.
>>Note: this is AND logic! To prevent a microsecond arc from turning into
>>a soldering iron and checkbook job, the amplifier needs ALL of the
>>So maybe it isn't so simple, after all...
>Why would an arc stop after one microsecond?  If the tube is gassy,the
>party is over.
>cheers, Ian
>-  Rich..., 805.386.3734,
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