SV: [AMPS] Re: SV: G2DAF

[Rich Measures]

>
>Lars Harlin wrote:
>
>>
>>-This is a plot from HP Spectrumanalyser taken about a year ago, and using 
>>speech - not
>>-two tone. Lower curve is for exciter alone....
>>
>>-Sorry for the bandwith, but guess a picture says more than a thousand 
>words....
>>
>>-73 de Lars/SM3BDZ
>>
>>Well, this did not seem to work - fileattachment. After another thought,  it 
>>might be just as good, especially
>>here on the reflector.
>>
>>So, anyone of you guys who find interest in seeing these plots, drop me a 
mail 
>
>>and I will mail you directly!
>
>Yes, please send me a copy, Lars.
>
>Can you also say what tube, what anode voltage, and how the screen
>voltage was generated (voltage doubler/tripler? solid-state rectifiers
>or vacuum tubes? Value of DC smoothing capacitor?)
>
>Something tells me that all of these details could be important...
>
>One risk with the G2DAF configuration is that a screen rectifier with
>poor efficiency would tempt the user to overdrive the whole amplifier in
>order to generate sufficient output. Thus there could be a lot of
>variation between a good G2DAF linear and a bad 'un. 

There should be little difference if the screen potential is not 
constant.  
>
>The choice of tube could also make a big difference between good and
>bad. As far as I know, all the original published work was done with
>813s and 4-125s.
>
813s and 4-125s have screens that follow the 3/2 power law.  

>In the late 1960s I had my education about SSB from listening to G2DAF's
>80m net, whose members were bitingly critical of poor-quality signals -
>so much so that like many other listeners I didn't even dare to check in
>for a report! Certainly there were several G2DAF amplifiers in use on
>that net, and if they hadn't generated a clean SSB signal the owners
>would have been flamed to a crisp after the first transmission.
>
>Later I met Dick Thornley a few times, heard him talk to clubs, and saw
>his construction work. He was a perfectionist in every detail

-  -  except one.

>and he owned his own spectrum analyser which was a real rarity in those days.
>Certainly he was the first to ask for criticism about his own signal
>quality. He also wrote a regular magazine column on SSB techniques when
>this was all new, experimental stuff. 
>
>So I am in two minds about his amplifier. Part of me says "This should
>not work." 

It isn't that it doesn't work, rather it does not deliver on the 
seemingly-miraculous promise of Class-C efficiencies And good linearity.  
 By supposedly delivering the miraculous, a guy takes on prophet-like 
status, whereupon groupie types will symbiotically follow and sing his 
praises for crumbs of approval.  .  We see a similar mechanism in 
religious cults.  The silent Bhagwan drove a fleet of Rolls Royces whilst 
his groupies swooned.  Meanwhile, back at the Rolls Royce dealer in 
Seattle, the salesmen said that the Bhagwan had plenty to talk about 
during his frequent purchases.  

>But having been around at that time, and known some of the
>people involved, I also feel that G2DAF would not have given his name to
>anything that put out a poor-quality signal.
>
The G2DAF-amp.  signals I listened to on the air had tolerable distortion 
levels on frequency.  The problem was the -22db/-23db adjacent splatter 
level when recommended amounts of grid current were being used.  However, 
when zero grid current was used, splatter understandably decreased.  
After complaints of splatter, I observed that G2DAF proponents would 
Temporarily lessen grid current to make peace.  
-  later,  Ian


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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