From: not.here@invalid.invalid   
      
   On Sat, 09 Jul 2011 21:25:39 +1000, Alex Pogossov wrote:   
      
   > "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.   
      
      
   It's probably traditional. :-)  Small, effective varistors are a newer   
   invention than valves. The two would never have met when the circuits   
   were being developed. That, and engineers having it hammered into them   
   that you *never* run a valve amp without a load.   
      
   --   
   Mick                      (Working in a M$-free zone!)   
   Web: http://www.nascom.info   
   Filtering everything posted from googlegroups to kill spam.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)