[Amps] Re: matching network

[Ian White, G3SEK]

R. Measures wrote:

>>you can safely operate *any* tetrode in class AB1,
>>cathode-driven. The requirement is that the control grid has the correct
>>negative bias, and the screen has the correct positive voltage. These
>>voltages are exactly as recommended by the manufacturer for class AB1,
>>grid-driven.
>>
>>For cathode drive, both grids must be grounded to RF. But in order to
>>apply different DC voltages, at least one grid cannot be connected
>>direct to chassis - it has to be RF-grounded through a bypass capacitor.
>>Because the recommended voltages are measured relative to the cathode,
>>all three power supplies (anode, screen and control-grid bias) generally
>>have to 'float' relative to the chassis potential.
>>
>>The correct DC bias voltages ensure that all the DC "grid" current goes
>>to the screen, and *none* to the control grid... in other words, correct
>>class-AB1 operation.
>
>**  Ian --  Is the power gain with cathode-driven and  no g1 current the
>same as with 'super-cathode' drive -- i.e., c. 5?

No.

In 'Single Sideband Principles & Circuits'  by Pappenfus, Bruene and 
Schoenike (aka the Collins company) they first describe GG triode 
operation, and quote typical power gains of 7 to 20.

They then continue: "Tetrode tubes can also be used in cathode-driven 
operation. The power gain is considerably higher, and is in the 20-to-50 
region."

They then consider semi-cathode-driven, super-cathode-driven and the RF 
feedback arrangement used on the 30S-1.

It's well worth reading.

>-  If g1 is never to be driven more positive than the cathode potential,
>why not connect it to the cathode?

It's all in that book.



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