Dear All,   
      
   I am seeking practical advice, further I am not a knowledgeable electronics   
   guy, tube or otherwise -- to say the least.    
      
   A few years ago I was fortunate enough to find and purchase a Sherwood S5000   
   II; I am into 50s cars and hot rods and just wanted the aesthetics and joy of   
   tube hi-fi ownership. A Sherwood expert here in the KC area completely   
   refurbished the unit with no    
   shortcuts taken. He only charged me for parts, not labor. Until recently my   
   5000S has provided excellent service for about two years of moderate use.    
      
   A couple of months ago the amp began generating some sort of signal spike that   
   resulted in conspicuously loud crackling noise through the speakers. Since I   
   do not use the amp's metal dust cover I was able to observe bright light   
   flashes emitting from one    
   of the four identical "power" (??) vacuum tubes situated at the rear of the   
   amp.   
      
   I pulled out the offending vacuum tube, which unlike its counterparts showed   
   discoloration at the "top" of the glass, presumably plasma vapor deposited   
   metal.   
      
   The tubes, I now know, are Russian built electro-harmonic 7591A units. I was   
   unable to contact the fellow who refurbished the S5000 II, so I went online   
   and found multiple vendors for the Russian 7591A tubes. I bought a "set" of   
   four, which I received    
   and which appear identical to the my "original" electro-harmonic tubes.    
      
   Now my reason for this query: The cross-sectional diameter of the   
   electro-harmonic 7591A units are too large to fit properly in the Sherwood   
   sockets. What gives?   
      
   A brief search online suggests to this novice that these modern aftermarket   
   tubes are (duh) fatter than the original electron tubes. I see mention of   
   aftermarket pin adapters so that tubes with similar electronic properties, but   
   different pin patterns,    
   can be substituted. Does such an adapter exist for my Sherwood sockets?   
       
   Alternatively, because the shape of the electro-harmonic 7591A glass housings   
   are slightly tapered cones (thinner toward the top) if one had a half-inch   
   tall adapter 7591-to-7591 the Russian tubes would then fit without   
   side-to-side glass contact,    
   assuming I alternated adapters at every other socket position. Does such an   
   adapter exist?   
      
   As it stands right now the four "new" tubes contact their respective neighbor,   
   with the outermost (2) tubes unable to fit squarely into their socket. Am I   
   correct in thinking that such glass-to-glass contact is not good for electron   
   tube lifetime? This    
   mechanical interference has to be putting stress on the glass, right? Should I   
   pay big bucks for NOS tubes that fit properly?   
      
   Any advise or suggestions will be sincerely appreciated. I guess it's not the   
   end of the world if I have to replace tubes often, but the present arrangement   
   seems pretty lame to me.    
      
   Thanks,   
      
   Charlie   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)