Tom Rauch wrote:
>> Note also that the input loading resistor was 300 ohms, not 50, so the
>> original G2DAF design was only suitable for tube exciters with a flexible
>> pi-tank output. Some people have modified the circuit for a 50 ohm load
>> using a step-up input transformer, but that may not develop enough screen
>> voltage, especially at 30MHz where stray capacitance may be a problem.
>
>Let me ask another question.
>
>The rectifiers heavily "load" the exciter in order to supply screen
>power.
>
>Was his original circuit as bad as the later offshoots where a peak
>storage system was used?
>
>What was the time constant of the screen source?
I don't know anything at all about the offshoots. The original circuit
was <apply visual imagination here>:
* 300 ohm grid resistor
* 0.005uF coupling cap to the junction between two 6U4GT's connected in
series as a voltage doubler
* 22k load resistor and 0.005uF smoothing
* screen current meter
* two screen bypass caps of 0.001uF each, also providing some smoothing
By the way, I do agree with G3VBL about G2DAF having been a very
knowledgeable guy and also a consummate craftsman. However, we also have
to remember that G2DAF was knowledgeable by the standards of 35 years
ago, when amateurs were still learning about SSB. Therefore the original
design was published as an idea for experimenters rather than a
completely proven concept - and then G2DAF died suddenly in early middle
age.
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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