This is the URL that works Ian.
http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-1.htm
BTW, is anyone stocking them in theUS? I called DEMI recently and they have
nothing left.
Carl
KM1H
----- Original Message -----
From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
To: <amps@contesting.com>
Sent: Sunday, January 29, 2012 3:36 AM
Subject: Re: [Amps] tetrode reverse screen grid current
> Hsu wrote:
>>I have a thought about shunt bleeder resistance ,If we use a HV MOSFET
>
> seial a resistor to replace it, when the negative screen current
>>happened,
> control the total resistance so the screen voltage still
>>constant, Is
> it a good idea?
>
> It works for me... and about 800 others, so far (shameless plug :-)
>
> <http://www.ifwtech.co.uk/g3sek/boards/tetrode-1.htm>
>
> Negative screen current happens in many of the tetrodes that we use for
> amateur-sized power amplifiers. Whether this is a practical problem will
> depend on many factors: the tube (not only the type, but also each
> individual example); the tuning, loading and drive level; and the screen
> voltage regulation.
>
> 'Negative screen current' forces current backward into the screen
> supply. This will tend to drive the screen voltage upward, which
> increases the screen-grid dissipation and the temperature of the grid
> structure, and thus causes even more secondary electron emission. If the
> screen supply fails to control the situation, it can quickly lead to a
> dangerous runaway - often ending in an anode-screen flashover.
>
> An active shunt regulator will hold the screen voltage far more constant
> than a passive bleeder resistor could, but it does need to be designed
> correctly. The voltage regulator also needs to be backed up by a current
> trip, to take the amplifier safely offline before any dangerous
> condition is reached.
>
> For more details about tetrode screen supplies, please see my QEX
> article:
>
> <http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-3.htm>
>
>
>
> --
>
> 73 from Ian GM3SEK
> http://www.ifwtech.co.uk/g3sek/boards
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>
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