Finding the G2DAF thread great entertainment.
Never built one myself, but like lots of the guys, I was around when amateur
SSB was being pioneered big time on the ham bands.
Great days.
Some observations on technical standards.
Yes, in those days some hairy signals were tolerated as people
experimented,but the majority of sigs were if anything cleaner than today.
People listened carefully and regularly asked for checks for splatter etc.
Incidentally, many of the the receivers were no slouches, either.
Something like, say, a Superpro with a Collins IF filter, or cascaded xtal
lattice filters, had an IF shape factor and skirt selectivity to die for.
Great front end selectivity, too . (Better than nowadays). Great signal
handling with the two rf amps throttled back.
Incidentally, the G2DAF receiver, strongly influenced by Collins 75A4, is
one of the best ham band receivers, ever.
Then as now, spectrum analysers were not thick on the ground, but people had
ears (used them more than generally the case today) and were quite capable
of telling the difference between -20 and -40 dB IMD even if they could not
put numbers to it.
The G2DAF linear has been published many times in the RSGBs "Radio
Communication" magazine. Almost always as 2x813. The users universally
report it to be a tractable and fine performing amp.
Radio Communication is a superb publication with high technical standards.
So far as IMD is concerned:
The British Isles are crowded, and many of the inhabitants love to complain
given minimal (or zero) provocation. (Out here there is a stereotype of what
is known as "the snivelling Pom).
There is absolutely no way that an amplifer design which characteristicly
puts out IMDs of the order of -20dB would have survived in that environment.
Now for some real excitement:
Who remembers the ZL linear?
Of and by Lester Earnshaw, of Kachina (and other) fame, plus other nameless
Kiwis.
Take an 813 (or two) or even a 4-1000.
Give it LOTS of plate volts. Big dropping resistor to an audio tetrode as
screen clamp tube. Clamp tube grid to the grid resistor of what just before
was a Class C rf amp and you have a ZL linear.
If you got it right, low distortion, low drive, put out loads of
power.....cheap and cheerful.
Dreadful if not set up right, and it was this aspect that led to its demise.
cheers
Baz, ZL1DD
end
Barry Kirkwood PhD ZL1DD
Signal Hill
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
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