4 7591 power tubes...

[Tom Phillips]

I've has good luck with the JJs.
I have not tested all the characteristics of the JJs but they do seem to bias up similar to old USA 7591s.

It's a shame that current distributors take such liberties with the tube models they market. A pet peve of mine is how they ignore things like such as size requirements which, after all, are one of the specifications for a given tube type. This really comes to light with the 7591 when you try to replace the power tubes in something like a Scott receiver. The JJ will fit even though it is oversize but the Sovtek is way too large.

[soundmasterg]

Interesting. Anything can happen; obviously we have technology today that was simply unavailable in 1965, so it is possible that EH and JJ could do this.

However, the 7591 was a very refined bit of tubemaking art. So it would be interesting ( if one was going to use 7591s on more than a onesy basis ) to get some of these and really do the comparison against the old 7591 specs.

In particular, EH didn't make any tubes back when I was tracking this; they bought Russian tubes and custom branded, this from the "sovtek" era. Maybe they have bought their own tube making capacity by now. I haven't followed it. The "slightly too big, may not fit in all spaces for the 7591" was the hallmark of the re-pinned 5881 in the day, so some caution is needed. Before I believed anything on the internet about a slightly too big 7591, I'd do the testing.

JJ does have the technology to make a 7591, perhaps even to make a consistently good one.

Anything is possible; but verify the "internet facts" before you bet any money or reputation on it.

EH/Mike Matthews owns the Reflector factory that makes about 60% of the world's tubes, ((Sovtek, EH, Tung-Sol, Mullard, Genelex, (Svetlana in US and Canada)) and quality of the tubes, and tube types best suited for the guitar amp market have gone up a lot since that happened. Unfortunately like most of the other tube makers both vintage and modern, there are shenanigans that go on with relabelling and what not that do make it hard to get to the core of the truth sometimes, and that is true in EH's case too. Having said that though, they do make excellent tubes these days, and while their 7591 is larger than vintage types, it is supposed to be very similar as far as it's other specs, according to some tube dealers I respect a lot like Jim McShane for instance. The JJ 7591 is supposed to have the same size and specs as vintage ones. I have a couple here of the JJ's but haven't compared them yet in a circuit. Bottle size does appear to be the same. I don't have any of the EH's, but once I build an amp I was going to compare all types as I do have a lot of vintage ones.

Greg

[Prairie Dawg]

Interesting. Anything can happen; obviously we have technology today that was simply unavailable in 1965, so it is possible that EH and JJ could do this.

However, the 7591 was a very refined bit of tubemaking art. So it would be interesting ( if one was going to use 7591s on more than a onesy basis ) to get some of these and really do the comparison against the old 7591 specs.

In particular, EH didn't make any tubes back when I was tracking this; they bought Russian tubes and custom branded, this from the "sovtek" era. Maybe they have bought their own tube making capacity by now. I haven't followed it. The "slightly too big, may not fit in all spaces for the 7591" was the hallmark of the re-pinned 5881 in the day, so some caution is needed. Before I believed anything on the internet about a slightly too big 7591, I'd do the testing.

JJ does have the technology to make a 7591, perhaps even to make a consistently good one.

Anything is possible; but verify the "internet facts" before you bet any money or reputation on it.

The problem you have to a certain degree with anything that is not new old stock or is imported from the Combloc is lack of standardization.

Time was when the EIA was the RMA and they were issuing standard specifications, if a tube maker wanted to put a part number on a tube it had to be qualified and substantiated that it met a given RMA specification-and that's why nobody had any heartburn in, for example, Sylvania making up an order with GE tubes that were relabeled. That's why you could drop an RCA in a socket that was built with a Hytron and never have a moment's doubt about the propriety of what you were doing.

However, RG, standardization to achieve equivalency is not the same thing as "It'll work OK and the pinout's right."

And unless a tube is qualified and traceable to a standard specification like an RMA/RETMA/EIA published specification, any label you put on it such as "STR" or "Special low noise 12AX7 Gold Series" or 7591X etc etc etc-well, all you know is that they're close enough to work in a socket.

And that's ALL you know.

Let's consider the dimensional aspect of tube pins, for example, and what that meant when a certain offshore manufacturer shipped a load of tubes with undersize pins a few years ago....although the military specification for octal tube sockets and pins is commonly available.

Lack of standardization and conformity to anything more than "Mike says it'll work-ship 'em out."

Now...the situation has improved over the past few years but it's still not the same thing.