On Monday, September 7, 2015 at 7:45:24 AM UTC-5, MarkS wrote:   
   > 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   
      
   THANKS MARK   
      
   Just the focused spot-on information I needed. If you ever need any info re:   
   old hot rods give me a holler.   
      
   Charlie   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)