[Amps] 50 watt stud mount zener diodes

[Mike Tubby]

  On 11/08/2010 15:45, Carl wrote:
> ----- Original Message -----
> From: "David C. Hallam"<dhallam at knology.net>
> To:<dezrat1242 at yahoo.com>
> Cc: "Amps reflector"<amps at contesting.com>
> Sent: Wednesday, August 11, 2010 10:03 AM
> Subject: Re: [Amps] 50 watt stud mount zener diodes
>
>
>> It's good that NTE can still supply them if needed, but their prices
>> take you breath away.
>>
>> David
>> KW4DH
>>
> Just another reason for 1N5408 or 6A10 strings. A tube arc will take out a
> 50W zener as fast as a 10W version.
>
> Carl
> KM1H
>

Carl, et al -

50W Zener diodes are now "hard to get" items in the UK - they are 
expensive, never quite the right voltage, noisy, and drift with temprature.

Have you considered making a "programmable Zener" using a TL431 and a 
TIP147 as per Ian G3SEK's "Triode Board" design (circuit attached).

The full Triode Board info can be found here:

         http://www.ifwtech.co.uk/g3sek/boards/triode/triode-manual.pdf

the grid bias circuit is on page 11 (and attached) and can be built on 
its own.  I have substituted one in to a 50MHz 3-500Z amp (the QST 1970 
design) and it works great.

This circuit is protected (assuming you have glitch resistors) by the VDRs.



Mike G8TIC








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