SV: SV: [AMPS] Re: SV: G2DAF

[Lars Harlin]

G3SEK:

>>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. 
>


AG6K:

>There should be little difference if the screen potential is not 
>constant.  


G3SEK:
>>
>>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


AG6K:


>-  -  except one.
>


G3SEK:

>>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." 
>

AG6K:

>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.  
>


G3SEK:

>>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.
>>


AG6K:

>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...
>


SM3BDZ:

Brilliant comments Rich. Somehow I feel Ive read you saying the same things before....

Pse excuse my bad humour Rich, but here in Sweden we have a special word when cows tjew and tjew
and tjew their food over and over again. I dont know the english word for that syndrom, but somehow - cant help it- it gives me associations to your argumental technique....;)

If you have two doors to your house, I´m quite sure that you have never ever used more than one and perhaps
cant even find the other door - cause you dont bother to look.....

Absolutely nothing personal Rich, I´m just not that good to express myself....

By the way, any comment you want to share with us regarding the plots I sent you last x-mas?


73 de Lars/SM3BDZ




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