[AMPS] Zener screen supplies

[g8gsq@qsl.net (Steve Thompson)]

-----Original Message-----
From: measures <2@vc.net>
To: Steve Thompson <g8gsq@qsl.net>; AMPS <amps@contesting.com>
To: <amps@contesting.com>
Date: 12 April 2001 16:48
Subject: Re: [AMPS] Zener screen supplies


>
>>
>>A different aspect to consider - what happens when there is anode-screen
>>flashover. I inherited a PSU (with 10x33V/5W zener screen supply) from a
>>friend. A dud tube caused a flashover and lots of damage.
>
>?  My guess is that the zeners shorted.  In such a case, shorted (0
>volts) zeners cause no damage.   (10) 5w zeners only cost around 11
>dollars.

Shorted zeners need replacing - I don't want to have to re-build the PSU
every time.

>>After some
>>investigation, I came to the conclusion that 375V VDR clamps on the screen
>>didn't protect anything, as their clamping voltage at 10s Amps is around
>>600V+.
>
>?  The 10 x 33v zeners would have shorted at far less than 600v.


They surely did.
>
>>The arc current went through the screen meter and shunt ...
>
>?  No glitch diodes for the meters is hardly good engineering practice.


Agreed - my point was that a screen circuit designed to run at 10ish mA
isn't an obvious place to need it.

Steve



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