Re: [Amps] 2879 biasing

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

Steve Thompson wrote:
> ----- Original Message -----
> From: Gene Bigham <jbigham2@kc.rr.com>
> To: <amps@contesting.com>
> Sent: 22 August 2003 19:18
> Subject: [Amps] 2879 biasing
>
>
> I have ordered a matched quad of these transistors to put into my mobile amp
> and need to build a bias supply for them.  Reading G3SEK on the subject gave
> some good pointers.  I want to use this behind a radio shack 10 meter radio
> that puts out about 25 watts.  Any further pointers or places to look for
> info would be appreciated.
> --------------
> The circuit Ian describes is simple and effective - other solutions I'm
> aware of are either more complicated or inferior, so why not try it? Another
> effective circuit is one used in Motorola app. notes with a 723 feeding an
> emitter follower. There's a selection of Motorola app. notes at:
>
> http://rf.rfglobalnet.com/library/ApplicationNotes/categories/1.htm
>
> For my interest, is there a definitive origin for the two transistor
> circuit? I first saw it in Philips designs from the 60s.

Likewise.

My web article shows why the bias circuits used in most amps are 
inferior and cause unnecessary IMD, and then explains in detail how to 
design this "classic" two-transistor circuit - the simplest one that 
really works.


--
73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
                           Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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