7591 Opinions Needed

[joel27]

I have a Fisher x101c that's cathode biased. If the price were the same would rather a matched quad of EH7591s or westinghouse tubes measuring at 48, 48, 58, & 56 with minimum good @36? Any thoughts will be helpful.

 

[BmWr75]

Matched E-H quads sell for about $90 delivered in the U.S. Closely matched vintage Westinghouse quads don't sell for anything near that price in my experience. Matched pairs appear to be selling in the $80-100 range on eBay. Guess I'd go vintage if the price was the same.

I have an X-101C running new E-H 7591s and it sounds great.

 

[joel27]

So you're saying the vintage are a close enough pairing to work as a matched set then? I guess that should have been my original question.

 

[Tubologic]

At the same price I wouldn't hesitate a second and go for the Westinghouse's.
As far as matching is concerned, the values given are useless If the measuring conditions are not specified. Are these real plate mA , transconductance , or some arbitrary "quality" values taken from an unknow tube tester ?
Remember the EH 7591's are electrically and structurally different from the original 7591 design and your amp may need some modifications to bias correctly the EH's. Also,they're taller and doesn't fit amp's with low profile cases. Even (moderatly) used N.O.S 7591's will give you longer and more reliable service than any currently produced replica's.
BTW, the X-101C circuit is not pure cathode bias but use the clever Fisher "mixed" bias scheme with an adjustable grid return path. Bias must be checked and adjusted for 40VDC at the 7591's cathodes after replacing the tubes.

 

[Bluelobster]

So you're saying the vintage are a close enough pairing to work as a matched set then? I guess that should have been my original question.

You need to first of all decide what it is you want to call matched. Getter shape? Date codes? Gain? Trans conductance? The criteria you decide matters plays a huge role. Life expectancy would be bottom of my list. Face it... tubes out production 30 years or better are going to be difficult at best to find matched pairs in parameters that matter, let alone a quad. These were getting scarce 15 years ago. I was buying old amps just to salvage the tubes then.
Maybe that quad of EH is looking better if your tossing money around. Find a reputable dealer that can give a good description of what and how he is deriving his numbers. They don't cost much more and the dividends are worth it.

 

[joel27]

The tubes were tested on a TV-7A/U tester if that helps. The price for the 4 westinghouse ones is only $100.

Thanks everyone.

 

[jaymanaa]

Go WH, it's a no brainer.:yes:

 

[tchuck]

I've had "matched quads" (I use quotations there because that's how they were sold, not because I tested any of them) of JJ and EH 7591s in my x-101-d for about a year each give or take. They were alright. Nothing to write home about and not really a staggering difference between them, but then again the amp sounds fantastic with everything I've used thus far. The amp came from the previous owner with tubes from four different brands (I can't recall what they were anymore) and aside from a slightly louder left channel it sounded good then as well. I'm currently running a NOS set of Sovteks that were tested and "matched" by a friend of mine. To be honest they are probably my least favorite.

One noteworthy detail regarding reliability - I had a defective tubes in the first JJ set and had to return them. Luckily I bought them locally and the guy was extremely accommodating, giving my another set of his shelf on the spot. The second JJ quad worked great until I started itching to try something new...

 

[skriefal]

$100 for the Westinghouse quad? Grab it! That's about half the going rate.

 

[Jailtime]

You can get those Westy tubes and give them to me.

Good vintage 7591s just aren't that common, grab them when you can.

 

[bhamham]

Those WHs are two matched Gm pairs. Matched on a TV-7 at around 150v no telling what they'll be with 400v on the plates and pretty slim that all four are matched for current draw. For that Fisher you'll need a matched quad for current. If it were an individually biased Fisher it's a no-brainer for the WHs or if you got a bunch more to pull from to match a quad.

Contrary to popular opinion I'd go for a matched quad of EHs (if they'll fit your case) from a reputable seller who matches Gm and current at operating conditions. Otherwise, you're going to probably drive one or two of those WHs to a very short life.

 

[Tubologic]

As bhamham rightly pointed out above, the X-101 doesn't allow individual bias adjustment for each ouput tubes, thus ideally the tubes must be matched in plate current at real operating conditions. The TV-7 (and about 99% of old tube testers of the repairman/shop variety) can't do such tests,only laboratory tube analyzers do.
Nevertheless, at $ 100 for the Westinghouse quartet I would not hesitate too much. If the tubes are of the same production and were removed from the same set chances are good that plate currents will be close enough, even if not perfectly matched. (a few mA difference doesn't matter here) . If you opt for new (EH) tubes you must ask the seller to match the tubes for plate current (mA) at real operating voltages, with no less than 350VDC plate voltage. If your tube seller can't do such tests better to look elsewhere...

 

[mikey5967]

I agree, go for the Westinghouse, unless you see a quartet of 7591s on ebay branded as EICO. Those will work great, and may be Westinghouse anyway.

 

[jaymanaa]

The only place matching really matters is in the circuit where the tubes will reside, and even there, I'll take close on WH units over new production in this particular tube number.

 

[joel27]

I got the WH tubes today. They happen to be Eico branded and bias well and stable in my amp. I think it was the right purchase. Thanks for the opinions.

 

[kvflyer]

I got the WH tubes today. They happen to be Eico branded and bias well and stable in my amp. I think it was the right purchase. Thanks for the opinions.

Great. I have zero experience with JJ or EH 7591 replacements so you will never hear my comments (as if they were valuable?). But I was fortunate enough to have acquired enough NOS and good used USA manufactured versions that I don't have to worry. I just know that in my equipment (properly restored and maintained) they just work and work daily with no issues.

They cost $1.61 in a mid 60s Allied Radio catalog (in mid 60s $$$ of course). Much has been said that both Fisher and Scott (and most likely others) drove those tubes very hard because they were an easy, inexpensive replacement. Today, that is not the possible. If one is not into cosmetics, the "coin base" version of this tube (talking vintage USA manufactures) is often much less in price because we all (myself included) prefer the look of the original Bakelite base. But the performance is the same.

I have and use the Soviet Military version of the 7189; the 6pi14pi-ev (6П14П -ЕВ) and have purchased but not used the Soviet Military version of the 6L6GB; the 6P3S-E ( 6П3С-Е), often stated to be a 6L6GC. But I don't think they are quite up to that standard. These guys may have been the re-pinned tubes that were initially sold as the 7591XYZ or some number like that. Just a guess though.

You can't beat a good pair (or quad) of Westinghouse 7591/7591A tubes. They designed the tube; they manufactured the tube and it was done right. Please, enjoy your tubes, "You done good!"