SV: [AMPS] G2DAF and super cathode

measures measures@vcnet.com
Fri, 17 Dec 1999 06:27:18 -0700


>
>Here we go again....;-)
>
>
>SM5KI:
>> >Before talking down the G2DAF circuit I may ask has anybody measured the
>> >distorsion  in it? 
>
>AG6K:
>> Yes.  In two units the total IMD was c. -22db below peak envelope power.  
>> One DAF amplifier used 813s.  The other used 4CX250Bs.  
>
>SM3BDZ:
>And from what I understand, measured by listening for the bandwidth, on 
>air. That will give you an idea of the quality ofcourse, but I would not 
>consider that methode to be acurate when it comes to precise IMD figures. 

Quite the opposite.  With a two-tone standard test, the DAF config. 
operates the screen at constant potential, the distortion looks ok, and 
there is no clue about what will occur during voice modulation.  During 
voice modulation, the screen potential varies at an audio rate from 
virtually 0 to hundreds of volts.  This is 'whole nuther ballgame'.  

>You cant be sure if you observe bad IMD in your own RX?  

hardly.  The guys that were getting splattered on at the time had 
receivers that were like mine.  [my receiver was a double filter type 
with a shape factor of 1.4,  6db-60db].  I used HP step attenuators to 
measure relative signal strength, so  S-meter accuracy was not a factor.  

> The other guys 
>TX?  Or both !? On the other hand, IŽve heard some amps with 4CX250 over 
>the years. They all had a very ugly distortion - and regulated 
>screen...;-) I should not blame the tubes, my guess is that most hams can 
>not handle those creatures....
>
>Myself, I also did some measurements on G2DAF circuit using HP Spectrum 
>analyzer/plotter and voice sample as signal source. I like what I see! 

But of course.  You could have DAF fever.  I saw a rather similar 
phenomenon in both of my pals who built DAF amps.  I saw pretty much the 
same phenomenon when three of my friends joined Kip McKean's Los Angeles 
Church of Christ, which is undoubtedly one of the cleverist and baddest 
religious cults on the West Coast.  The happy ending is that the three 
bailed out of the cult and the two converted their DAFs to regular amps 
that were only slightly less efficient, but way cleaner.  .  .  
>
>SM5KI: 
>> > Where and when was this published?
>
>AG6K:
>> It was published live on the 40m band whenever people were being 
>> interfered with by a  DAF amplifier. .  I was the publisher.  
>
>SM3BDZ:
> I ve published the results as email and imagefiles to interested people, 
>among them AG6K.
>With some exception, I ve also received positive response from these guys.
>
>The exception is AG6K....;-) You didŽnt say a word Rich....

True.  I try not to talk much.  When my three friends joined the 
nasty-cult, they were the happiest that I have ever seen them.  I told 
them this  "keep your eyes open and your ears open".  Fortunately, they 
did.  When the two DAF builders ran two tone tests, they were happy guys. 
 When I told them what the voice distortion level was they pretty much 
wanted to lynch me.  I never told them that the DAF was a daft design at 
any time.  
>
seasons greetings, Lars

-  Rich..., 805.386.3734, www.vcnet.com/measures.  


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