[AMPS] G2DAF and super cathode

[Ian White, G3SEK]

Skipp wrote:

>OK, I missed the start of all this again.  Is the G2DAF design just
>another super cathode drive amplifier? ...  or is the hook for the
>circuit a positive potential on the screen grid..?  Someone please tell
>me "the hook" about the daf amp circuit. 

The G2DAF is grid driven across a load resistor, with grounded cathode.
The unique feature is that it has neither grid bias nor permanent screen
voltage. Instead, the screen voltage is derived by voltage-doubling the
RF voltage developed across the grid resistor. At peak drive there is
significant grid current - obviously so, because there is no negative
control grid bias.

The grid resistor in the original was about 300 ohms IIRC, so it was
only suitable for tube-type exciters with a versatile pi-network output. 

The original tubes were two 4-125As in parallel.

There have been various amplifiers described as "G2DAF", but it is not
known whether these truly followed G2DAF's prototype in all important
details. For that matter, it is not known what the important details
really *are*.

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

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