K2AW Frank has excellent prices on 50 watt zeners...Also for those wanting
an adjustible bias for the common ham triodes see: http://gs35b.com/bias/
Tony has developed this small board and the price is right too..I`m using
one with a 8877 and it works great...Jim...K7RDX..
----- Original Message -----
From: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
To: <amps@contesting.com>
Sent: Tuesday, November 07, 2006 3:37 PM
Subject: Re: [Amps] FW: Zener Bias Replacement
> Steve Thompson wrote:
> >
> >
> >Larry Carman wrote:
> >> OK... you all have sold me on the idea of using zeners instead of
standard
> >> diodes. At least by using standard diodes I have determined the bias
voltage
> >> I need. Now I have to find a zener supplier that will accommodate a
poor
> >> mans budget.
> >> Regards to all and thanks for the info.
> >How does a smaller diode with a big transistor fare (for example, see
> >the very bottom of http://i5uxj-2.cln.it/amp/schemi/w6sai/w6sai.html) -
> >or a big transistor with a TL431 as in the G3SEK 'triode board'? Either
> >will likely be a lot cheaper than a high power zener.
>
> Sorry, I'm pushed for time at the moment, and unable to reply in great
> detail.
>
> The circuit for a high-power 'adjustable zener' comes straight from the
> TL431 data sheet. Both WD7S and I have used it in our triode control
> boards, because it gives a highly stabilized bias voltage that is also
> fully adjustable.
>
> The schematic is in my Triode Boards manual, downloadable from the
> website below.
>
> Somewhere in the AMPS archives is a cost breakdown that showed this
> circuit works out cheaper than a 50W zener at new-parts prices (try
> searching for "TL431").
>
> On the road again tomorrow...
>
>
> --
> 73 from Ian GM3SEK
> http://www.ifwtech.co.uk/g3sek
>
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