From: apogosso@tpg.com.au   
      
   "Alejandro Lieber"  wrote in message   
   news:k5aemj$11pc$1@adenine.netfront.net...   
   > Alex Pogossov wrote:   
   >> "Alejandro Lieber"  wrote in message   
   >> news:k54s5k$2r6g$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:   
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   >   
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