>Make sure to distinguish between grid bias supplies with truly regulated
>output (with feedback) and bias supplies with low output impedance. It's a
>lot simpler to make a stiff supply by resistively loading the bias supply
>output it is to actively regulate it.
>
** amen. Sophisticated electronic regulation in high RF fields is
definitely not a piece of cake.
>If one does choose to regulate the grid supply make sure it can handle some
>grid current, analogous to the screen supply having to handle reverse
>current. This probably means a shunt regulator
** The circuit at:
http://www.somis.org/D.a.04.GIF
can easily handle 10mA of grid current, it switches electronically in
>10uS, and it is not regulated because it does not need to be for AB1 because
zero-current is drawn -- provided of course that a competent operator
tunes up the amplifier. The good news is that if an unethical operator
decides to run the amplifier in AB2 in hopes of getting an extra tenth of
an S-unit or so of P-out, he/she will not be able to get enough grid
current with an unregulated grid bias supply.
>
cheers, Jeff
>----- Original Message -----
>From: "Ian White, G3SEK" <G3SEK@ifwtech.co.uk>
>To: <amps@contesting.com>
>Sent: Tuesday, December 30, 2003 5:46 PM
>Subject: Re: [Amps] 3.5 kV 2A REGULATED Power Supply: Schematic ?
>
>
>> R. Measures wrote:
>> >** The grid does not and can not draw current when a competent
>> >operator sets the grid potential just above the level where it can draw
>> >grid-current with the max PEP drive that's available.
>>
>> That is only true if the grid input circuit is guaranteed to be able to
>> soak up all possible levels of drive without allowing grid current...
>> but that also has disadvantages: either the exciter runs flat-out and
>> generates unnecessary IMD of its own, or else the exciter runs at a
>> lower level and the amplifier is seriously under-driven.
>>
>> I truly cannot see why anyone should design (or defend) a high-impedance
>> bias supply whose voltage regulation will collapse at the first trace of
>> either normal or negative grid current. What's the point, when a
>> better-regulated supply is just as easy?
>>
>>
>> --
>> 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
>> Editor, 'The VHF/UHF DX Book'
>> http://www.ifwtech.co.uk/g3sek
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|
