From: apogosso@tpg.com.au   
      
   "Phil Allison"  wrote in message   
   news:97qci7FeldU1@mid.individual.net...   
      
   > ** Cos the usual RC network suppresses the spike sufficiently, along with   
   > the load.   
      
   If a load is connected -- correct. If no load, then as I have mentioned you   
   need microfarades + several kiloohms to absorb it, not a few nanofarades   
   usually connected to dump HF ringing of the leakage inductance.   
   >   
   >   
   >> Or is the assumption that no one will be changing tubes on a working amp?   
   >   
   > ** Well, not with no load connected.   
      
   What about an amp being fool proof then?   
      
   >> Or occasional arcing and sparking is not a problem?   
      
   > ** The Aussie made  6V6GT  used in my first valve amp liked to spark   
   > internally with no load. Never did it, the A&R OP tranny or the socket any   
   > permanent harm. But if you wanna go belt and braces -  fine with me....   
   >   
   > BTW  -  how much HT have you got ??   
      
   Only 250V. But I do not want to risk any possibility of insulation breakdown   
   in an old lousy OPT.   
   Probably a small varistor rated at 350...400Vdc and with less than 500pF of   
   capacitance will be OK.   
      
   The tread is also of  general nature -- why do not we see varistors in the   
   tube amp circuits. Probably you are right -- no one suffered serios damage   
   of this particular stress mode.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)