From: maschuckert@gmail.com   
      
   On Sunday, September 6, 2015 at 3:00:42 PM UTC-4, cli...@kumc.edu wrote:   
   > 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   
      
   Hi Charlie,   
      
   Glass to glass contact is not great idea. Beyond NOS 7591A's, there are other   
   options. Right up front, I do not have any personal experience with the new   
   production 7591A's, just NOS- but these days, that can be a crap shoot as   
   well. Anyway, JJ makes a    
   7591A that is the same diameter as NOS so they should fit better. Also, the   
   same company that makes the Electro Harmonix 7591A's (New Sensor) also   
   released a so called "re-issue" Tung Sol 7591A. I believe these are the same   
   diameter as the JJ / NOS but    
   appear to be 2x the price of JJ's. If I were going to new production, I would   
   probably go with the Tung Sols.    
   The spacer idea is neat but you may have to make those yourself. Use a tube   
   socket and tube base. There was a time when the 6GM5 was an NOS 7591A   
   alternative but had a different base so an adapter was needed. The price of a   
   6GM5 is up there now an NOS    
   7591A anyway so the climb might not be worth the view.   
      
   BR's,   
      
   Mark      
      
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