From: info@turneraudio.com.au   
      
   On Saturday, 13 October 2012 16:12:47 UTC+11, Alex Pogossov wrote:   
   > "Alejandro Lieber"  wrote in message new   
   :k5aemj$11pc$1@adenine.netfront.net... > Alex Pogossov wrote: >> "Alejandro   
   Lieber"  wrote in message >> news:k54s5k$2   
   6g$1@adenine.netfront.net... >>> Very    
   interesting. Do you know if it has been done in practice ? >>> Will the final   
   valve still work in class C all the modulation cycle ? >>> >>> I also remember   
   seeing a rig using 2 6W6 (or 6Y6) in parallel in the >>> cathode of the RF   
   output valve. >> >>    
   Cathode modulation has more advantages. >> >> 1. It is a sum of control grid   
   modulation and partly screen modulation. >> As >> the cathode voltage rises at   
   the troughs of modulation, voltage >> difference >> between the screen and   
   cathode reduces. Thus    
   the "pull" of the screen >> grid >> reduces which cooperates with the effect   
   of the cutting of by the control >> grid. Thus the cathode voltage excursions   
   are smaller than control grid >> excursions if it were purely grid modulation.   
   >> >> 2. Modulation    
   is not affected by variation of excitation voltage. In a >> common grid   
   modulation, if the excitation voltage say is modulated by >> 50Hz >> hum,   
   output will also be modulated. With the proposed cathode current >> modulation   
   output will not be affected.    
   Cathode voltage might be >> modulated >> by hum, tracking it like in a cathode   
   detector, but since the current is >> stable, the anode RF component will be   
   almost unchanged (ignoring cut-off >> angle effects). >> >> But the greatest   
   advantage is no need    
   for any adjustments of bias, etc. >> The >> only thing to be set is the   
   cathode current. It is done by adjusting bias >> on >> the gate (base) of the   
   modulator series transistor. >> > Very interesting. > Where can I look for a   
   practical circuit ? Nowhere.   
    The whole fun is to create this circuit and experiment. Patrick has done   
   similar thing (cathode current modulation) in his low distortion test AM   
   modulator. You have a chance to try in a higher wattage range. I did it many   
   years ago with a smaller tube,    
   similar to 6BW6, for a 10m band transmitter. Regards, Alex > > -- > Alejandro   
   Lieber LU1FCR > Rosario Argentina > > Real-Time F2-Layer Critical Frequency   
   Map: > http://1fcr.com.ar > > --- news://freenews.netfront.net/ - complaints:   
   news@netfront.net ---   
      
   One small tube which might be good for G3 AM modulation could be the small   
   mini 7 pin 6DT6, because it was common for an FM demodulator using quadrature   
   detection, but fairly simple, and 6DT6 was made to have good G3 gm character.   
   Once the RF is AM modulated, it can just be amplified by a following RF output   
   tube, maybe 1 x 807 is good.    
      
   Patrick Turner.   
      
   --- SoupGate-Win32 v1.05   
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