>
>
>Before talking down the G2DAF circuit I may ask has anybody measured the
>distorsion in it? Where and when was this published?
>
>There is much about the G2DAF in Pat Hawkers TECHNICAL TOPICS SCRAPBOOK
>1990-94 and in other RSGB technical publications such as their older RADIO
>COMMUNICATION HANDBOOK. The new 1999 edition is just send out - as soon as
>I receive my copy I will let you know more about it. RSGB = Radio Society of
>Great Britain.
>
>The super cathode version of the grounded grid has been discussed by W6SAI
>and WA6BAN in QST 7/67: SEMI and SUPER-CATHODE-DRIVEN AMPLIFIERS. The same
>authors analyzed the GG: THE CATHODE DRIVEN LINEAR AMPLIFIER in the QST
>6/67. Very interesting basics.
>
>They gave an example of a 4CX300A with the grid tied to the cathode and
>screen grid tied to ground. The no signal grid voltage was of course = 0 and
>the no signal anode current = 15 mA. With 75
>watts of drive they got 375 watts out at -46 db 3rd order products. Screen
>voltage was 330 volts peak delivered by the driver. They did not publish
>how
>much anode dissipation, but it should have been low. Small fan needed then?
>
>What is the practical use of such a low gain circuit? Well, in a single
>frequency linear amplifier, where the tune up of many tuning circuits is no
>problem, you could use a number of cascaded super cathode stages for a real
>simple low distorsion linear. Very clumsy solution but the distorsion
>figures are impressing, are they not?
>
>I also remember also an old CQ article by a guy running a 4CX1000A as a
>super
>cathode linear. All electrodes had normal DC voltages except maybe the
>screen grid voltage which had lower DC voltage because the rf cathode
>voltage added.
>The grid was tied to the cathode with a couple of noninductice caps. As far
>as I remember the tube was run in AB1? In order to get a large output, you
>had to use up to 150-200 watts driving. And
>that is exactly what you have in some modern transceivers. As far as I
>understand, and I may be wrong, this circuit should have very low
>distorsion. If you then drive it with a transceiver with 28 volt final
>transistors, you get lower distorsion there too than in one with 12 volt
>transistors in the final? You never need any external ALC and best of all:
>you have not to bother about any grid
>current because there aint any, hi ( the 4CX1000A has a v e r y l o w
>max
>grid dissipation )!
>
>Nothing new under the sun then and again: let us scan old articles on
>linears into a CD disc or let it be avaiable on the net. A good start would
>be if someone please sends me the email adress of Reid Brandon/ EIMAC to get
>permission to copy EIMACs Amateur Service News Letters to be distributed
>on the net. I send a mail to Bill W6SAI but no answer so far.
>
>Now, waiting for the storm to break out from the G2DAF haters club,hi!
>
>Hej daa de Hans SM5KI
>
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