f622856c   
   From: apogosso@tpg.com.au   
      
   "Patrick Turner"  wrote in message   
   news:2169d98c-5935-4e7c-   
      
   When you have measured and demonstrated your technique and analysised   
   it all with maybe 10 detailed pages on a website with photos of the   
   amps, then ppl might say you have something to offer. People here are   
   very difficult people. We cannot agree with anything anyone says   
   unless they offer the truth, the whole truth, and nothing but the   
   truth, so help them in the eyes of the God Of Triodes :-)   
      
      
   > At LF one lag subtracts from two leads and in combination we have only   
   > +90deg below 10Hz. Therefore, 0dB line at about 3Hz (typically) will be   
   > crossed safely at only +90deg!   
      
   I'll believe works when I see it.   
   >   
   > Killing many birds with one stone:   
   > - perfect transient with no peaking;   
   > - natural low cut off in the whole amp (sort of built-in anti-rumble   
   > filtering);   
   > - reduced error signal at VLF as more feedback is applied;   
   > - no need to use two identical shelving circuits in push-pull amps -- just   
   > one extra electrolytic.   
   >   
   > A drawback - a despised electrolytic as a shaping component.   
      
   Perhaps there are other drawbacks you have not thought about.   
      
   I suggest you embark on a course of soldering in your laboratory to   
   prove your idea works. We all look forward to results.   
      
   Alex:   
   I am not into building audio tube amps, because it is crazy to do while SS   
   works (or can potentially work) much better in all respects, apart from   
   creating a warm fuzzy feeling. But I restore and improve radios, and use   
   this feedback increase at LF technique. Of course there is no rumble in an   
   AM receiver, but fadings, beating of two stations on close but not   
   synchronised carriers and simply skimming the band makes lots of VLF.   
      
   As you know to minimise AF load on the AM detector, it is not uncommon to   
   have grid leak in the first audio stage of 10M with 0.05uF of coupling cap.   
   This huge time constant makes the first tube (6SJ7, e.g.) virtually open to   
   DC. VLF undulations result in 30V swings on the plate of the 1-st stage   
   bringing it close to saturation. Part of this reaches the grid of the power   
   stage (say, 6V6) unnecessarily swinging its bias and plate current. The   
   later in turn cause undulations on the lightly filtered +B rail, and even   
   might fall into resonance with the supply CLC filter.   
      
   I am not very impressed with the shelving approach, because it is only an   
   attenuator. While it would cut off 6V6 grid excursions, it will not prevent   
   from 6SJ7 front overloading.   
      
   Instead I use a circuit which helps reduce VLF voltage applied between grid   
   and cathode of the first stage 6SJ7.   
      
   You would say: Use a low cut-off filter. But it is a complication. Much   
   better is to turn the amp into an active high pass filter by means of the   
   NFB.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)