From: info@turneraudio.com.au   
      
   On Monday, 27 October 2014 08:45:00 UTC+11, jurb...@gmail.com  wrote:   
   > Is there something special about electrons going through a vacvuum instead   
   of a piece of silicon or germanium ? (there are avtually other materials   
   possible but not widely used)   
      
   All devices have differences, which make them different but not necessarily   
   special which is an emotional term, no?   
   >    
   > Noe thing I seee about tubes in the output, which is where "it" happens, is   
   that no matter how many elements a tube has, it is still a rectifier. It is   
   still a diode.    
      
      
   Tubes with only anode and cathode are diodes. They are used to rectifying,   
   unless used as slow turn on resistances after heating up. Tubes with one or   
   more control grids *could* be used as a diode but since about 1903 have been   
   used as switches or    
   amplifiers, so the use defines what the tube is, and most tubes are   
   amplifiers, and never considered to be a diode.    
   >    
   > What that means is that when the tube conducts into an induxtance, there   
   might be a freewheeling effect of sorts. The voice coils of the speakers are   
   inductive, as are of course the windings of the transformer.   
      
   There is no "free wheeling effect of sorts" as defined in any text books.    
   To know what you are talking about, you need to fully study LCR theory and   
   behavior of combinations of L, C, & R in such things as speakers.    
   The free wheeling you are talking about is not like momentum in moving objects   
   but is being confused as the release of magnetic energy when current in an L   
   is cut off. When a tube anode has an L to B+ and the tube current, Ia, has   
   steady level, say 50mA,    
   then a low voltage is across L. If tube turns on more so Ia = 60mA, and speed   
   of Ia change is fast enough, then anode voltage Ea goes negative with only   
   10mA change in the inductance. If 60mA is maintained, the change of voltage   
   reduces and L has only    
   the low Vdc across the coil, and Ea has hardly changed from when you started.   
   If the 60mA is reduced to 50mA, then you see a rise in Ea going more positive.   
   How can this be because Ea rises above the B+ supply? Its counter intuitive,   
   because common sense    
   can't explain it, so YOU need to abandon all your common sense ideas when   
   considering electronic phenomena. Now when Ia is reduced, the reduction of   
   current in L causes the voltage across it to change phase, goes + instead of   
   -.    
      
   Now this sort of observations plus hundreds of other is what you ought to be   
   doing in a workshop with meters, R, C L and some old tubes and a PSU and then   
   by observation you get to understand behavior which absolutely baffles all   
   those who never study    
   anything, ie, most of the population.   
      
   > I think the effect of this is most pronounced at or near clipping, as not   
   only this inductance comes into play, but possibly even the inertia of the   
   speaker cone(s). I believe that this largely accounts for that special sound   
   of certain guitar amps. In    
   fact, while it doesn't happen much, they used to take and mike a little Fender   
   amp in a box at a concert because they could not duplicate the sound.    
   >    
   > Well, I have been thinkiong about this for a time and come to a few   
   conclusions.    
   >    
   > When you use negative feedback, most of that tube sound that was due to   
   nonlinearities etc. is gone, or near gone. You didn't want that anyway.    
      
   >    
   > The effect is not necessarily limited to at or near clipping. I am not sure   
   now to demostrate it but describing it mechanically might work here. Consider   
   an automatic transmission in a car. In the 1970s, some of the best of the were   
   developed. What    
   they did was to have the first and second gears on a one way clutch. Thisa   
   means that taking your foot off the gas does not slow the vehicle down like it   
   would in a stickshift. It would freewheel.    
      
   Cars and Fenders cannot be compared to understand electronics.   
   Each are what they are, and I am asking what am I learning here?   
      
   Clipping when you see it means the amp has no voltage gain when wave line is   
   flat, and the harmonic content of the wave rapidly increases after clipping   
   begins from say 3% to 40% if the tube is over-driven 10 times the input   
   voltage needed to make the    
   amp clip. So the Fender becomes a mere switch when over driven, and simply   
   passes square wave signals to the speakers. The speakers   
   have some L combined with R so if you examine the wave form at speaker the   
   waves are not nice clean square waves, but have undulations and ring   
   frequencies, and many ppl like the sound of such high THD. Notes have edge and   
   power, and the rock'n'roll    
   industry would be fuckt without this THD, all would sound dull, but before   
   rock, much more subtle H were wanted in music notes, and we had hundreds of   
   years of evolution of instruments, all of which produced a range of notes,   
   some clean, like a flute,    
   some dirty like a saxophone, and then came ppl who used clean notes fed though   
   amps which were over-driven, and ppl liked the range of note quality. Well   
   before gross clipping occurs, tubes can impart warmth to notes, as in quietly   
   played jazz guitar.   
   But I digress,.......    
   >    
   > The advantage to this was that it could simply shift into the next higher   
   gear without worry ing about the engine RPMs. In later cars with front wheel   
   drive, they usually do not have the one way clutches which makes the shift   
   points critical. In the    
   1990s etc., those shift point were controlled be a cable from the throttle   
   among other things, and if not set right it would clunk hard when slowing down   
   to a red light or sometning.    
   >    
   > In the old THM trannies, or Ford C6 and Chrysler A-727, they could set the   
   shift points wherever because it would shift smooth anyway, because of the one   
   way clutch.    
   >    
   > Now think of this with a speaker cone. It is only pulled, one direction as   
   well as the other, but always pulled, never "stopped" or damped. the only   
   damping that would happen would be if it is driven hard and the oppossite   
   outpuit tube conducts.    
      
   Speaker cones are subject to magnetic forces at all times during the wave form   
   applied to it and with a square wave, the flat part STOPS the cone movement.   
   The voltage change ceases, magnetic force change ceases, but speaker is HELD   
   tight for an instant    
   before voltage change returns.    
   >    
   > Of course the characteristics of the OPT and speaker system are at play, but   
   the major difference in the amp is that the tube is a rectifier. If the plate   
   voltage wants to go lower than the grid voltage calls for, it can. In fact it   
   can go negative.    
      
      
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