I would like to ID the US maker of a quad of identical 7591A Fisher tubes I have. They all have tan bases, like some Westinghouse I have seen. THE FISHER and address printed on glass. Right of that is code ED. Date code 64-22 on glass. Etched on top of glass envelope is 7591A, above that in smaller case, is Made in U.S.A. and there are random dots above and below the type number, also. I am thinking maybe Westinghouse or Sylvania? Mulling over what to do with my free attic find X-101-B amplifier, which I have not touched since I got it and stored it. Pondering cost/benefit, I decided that one thing, is a quad of those tubes is $$$ so I tested them first, and they are all very good. Without taking the case off, I can see that one of the Fisher 12AX7 tubes is made in Holland, so I assume maybe Amperex. I may want to fix this up and use in a second system in here and for some reason have been shy of messing with it. Shows age but is not ate up or rusted at all. Cosmetically decent and would be near excellent with a little effort. Electrically is ? I find schematics for 101-C online but not the -B. Owners manual has no schematic.

7591s with the tube number printed on the top of the glass bulb usually are made by Westinghouse. Is there a "337" printed anywhere on the tube base or glass? That's the manufacturer code for Westinghouse.

There are no markings whatsoever on the sides of the base. And the bases are that light tan color like some Westinghouses that I saw for sale, but I was not assuming that they were necessarily the only makers that made that color base. No 337 seen anywhere.

Okay. Sounds like someone cleaned the tubes, removing the labels. In any case, the top-bulb labeling is pretty much a dead giveaway that they're Westinghouse tubes.

Here's a photo of some Westinghouse tubes for comparison:
http://audiokarma.org/forums/showpost.p ... ostcount=4

Yea that pretty much clinches it. The only diff on the top is that mine are A's and have more than one dot above the numbers. I doubt they were cleaned off at the base. Unless that was left off when they applied the Fisher trademark to the glass. There is a quad of these for sale on ebay right now. There is 1964 written on my manual and the tubes are dated 64 so I think they are 99% likely the original tubes in it. And they all test strong. So next is to take it out of the case and see what might need to be done to make it useful.

If memory serves, the 7591 was a Westinghouse development. I'd suspect that most 7591's branded by amp/receiver manufacturer trademark (i.e., Fisher, Bogen etc) came from Westinghouse, especially the ones with the tan bases.

Larry

Yes, W is listed as the registrar and with GE, RCA, SYL, TS also producing.

Carl

TS = Toshiba? I know that they made 7591s. But I've never seen anything suggesting that Tung-Sol did. Or RCA for that matter -- although they certainly did re-label GE/Sylvania tubes.

TS = Tung-Sol.

L

Tell it to Lud

Carl

Lud? Are you referring to Ludwell Sibley? That's all I could find via a quick Google search.

Yup

Unfortunately his 'Tube Lore' book seems to be out of print and unobtanium.

"Tube Lore" (pg 83) lists the 7591(-A) as a Westinghouse tube with GE, RCA, SYL, and TS as alternates.
The -A has the same specs as the non-suffix type.

Variants are 6GM5 and 7868.

7868 is listed (pg 87) as an RCA and GE variant of the 7591-A.

The ED code would be January 1973 if the tube follows the RCA date code pattern for that era.

IIRC, one if the issues of Tube Collectors of America monthly publication gave the data on the dots as to the plant & mfg. Altho I may remember wrong on that.

Well the quad of identical used Fisher output tubes on ebay(exactly like in mine) went for 255$, add to that the bunch of Fisher/Amperex 12AX7 tubes and I may have 400$ worth of tubes in the thing! THen if I parted out the chassis for the faceplate, knobs, case, and transformers, that could be another 300$ or more. So I could make alot of money off my "free" Fisher amp without even doing anything to get it going again! But that gruesome end is not the plan for it right now. Still I wonder if in working condx. it would sell for as much as the parts.

You could likely get more at $300 American dollars than 300$ of whatever youre using

Carl

When tubes were cheap, nobody thought twice about changing them every few gigs, and kept us in pretty good employment serving them. Kind of like tires and brakes, we expect them to wear out. That was long ago.

Tame down load on otherwise OK 7591 sets and they might outlast all of us.

I've been urging this for years with any of the large-cathode output tubes (7591, 7868 etc). The great weakness of these tubes is their tendency toward grid emission and subsequent runaway. Overheating is the culprit. It seems that in almost every case, they're installed in equipment designed to run them to redline, and that was on AC line voltages generally lower than they are now.

For their sake and the sake of your equipment, gear back such tubes to run them cooler. You'll be sparing your transformers as well. Raise the bias, insert cathode and screen safety resistors. Run the equipment itself on no more than 110v (via bucking transformer, Variac, or whatever). You won't lose any performance that you'd miss anyhow; instead, you'll dodge any number of service nightmares (and costs).

Larry

+1 Slow it down voltage wise so you need not scrounge for replacement tubes very often. New ones are not as good as old ones, no surprise. Reworked properly and in conservatory manner new ones can give very good service indeed. Price point prevails.