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[email protected] clittle@kumc.edu is offline
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Default Restoring a Sherwood S-5000

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, 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 old hot rods give me a holler.

Charlie