4 7591 power tubes...

[Bmxbarspin724]

I have 2 amps that both use a pair of 7591 power tubes with various preamp tubes. I was wondering if there were any amps that have been made that use 4 7591 power tubes. I looked and all I found was some old fisher hi-fi stereos that used them.

I really like the sound of the 7591 tube, as opposed to a 6L6 quad, or an EL84 quad. But the amps that I have found that use 7591's seem to put out at most, like 30 watts, and I really would like to have like 50+ watts.

Is there something inherent about the 7591 tube that disallows it to be used in a quad?

what's up with that?

[Jazz P Bass]

I would not think the tube itself would care how many you use in parallel The circuit itself would.

[Tom Phillips]

There is nothing inherent about the 7591 tube that disallows it to be used in a quad. It is just from an era where the designer would change to another tube type if power output in the 50 watt region was desired.

[Prairie Dawg]

Originally Posted by Tom Phillips

There is nothing inherent about the 7591 tube that disallows it to be used in a quad. It is just from an era where the designer would change to another tube type if power output in the 50 watt region was desired.

Another thing is whether the RCA salesman or the Sylvania salesman stopped by shortly before the particular production run and offered product at sale prices.

[Rhodesplyr]

Originally Posted by Tom Phillips

There is nothing inherent about the 7591 tube that disallows it to be used in a quad. It is just from an era where the designer would change to another tube type if power output in the 50 watt region was desired.

Exactly. I think the target application for the 7591 was integrated Hi-Fi amps where it frequently superseded the EL84/7189 in amps by H.H. Scott, Sherwood, Fisher, etc... It allowed designers to get 30-35W from a pair of fairly small power tubes that required only 800mA of heater current per tube and that were easier to drive than, say, a 6L6 or 5881. Though I've never owned a 7591-based Hi-Fi amp, those who do seem to like them a lot.

Hammond use them in a few of their later designs.

[Jazz P Bass]

I have two pairs of these 7591 tubes in my Fisher 800-B.
I think it is a synergy thing. Fisher- 7591. This amp sounds awesome.

[capnjuan]

Originally Posted by Bmxbarspin724

I was wondering if there were any amps that have been made that use 4 7591 power tubes ... I really like the sound of the 7591 tube ... but the amps that I have found that use 7591's seem to put out at most, like 30 watts ... is there something inherent about the 7591 tube that disallows it to be used in a quad?

Hi; Panaramic / Audio Guild amps from the mid-60s used quads of 7591As (one is missing from its socket):



The power output of tubes is a function of the ability of tube to handle voltage on its plate and current. Link to the Tube Data Sheet for the 7591A:

http://www.tubezone.net/pdf/7591.pdf

The tube was very popular in the mid-60s because of increased power handling / cleaner tone v. 6V6s; Ampeg, Gibson, Guild, Audio Guild ... many others made 7591 amps ... usually 25-30 watts for push/pull twins. I don't know of any other quad 7591 designs. CJ

[ivan100000]

From my experience, the 7591 is not a great choice for a guitar amplifier; it's a hi-fi tube. My McIntosh 225 sounds fantastic running a quad of the 7591, but my Ampeg J-12 (2 x 7591) sounds too clean & simply won't break up like a 6V6-powered Fender will.

[Tom Phillips]

Originally Posted by ivan100000

From my experience, the 7591 is not a great choice for a guitar amplifier; it's a hi-fi tube. My McIntosh 225 sounds fantastic running a quad of the 7591, but my Ampeg J-12 (2 x 7591) sounds too clean & simply won't break up like a 6V6-powered Fender will.

Understood but it's not just the power tube itself but the whole amp circuit that determines breakup.

[JerryP]

I love the 7591 in a guitar amp. Hilgen used them and they sounded like a cranked Marshall at low volumes. Gibson used them too and they had a pretty sweet tone. I'm in the process of building an amp based on that tube.
Jerry

[soundmasterg]

Originally Posted by ivan100000

From my experience, the 7591 is not a great choice for a guitar amplifier; it's a hi-fi tube. My McIntosh 225 sounds fantastic running a quad of the 7591, but my Ampeg J-12 (2 x 7591) sounds too clean & simply won't break up like a 6V6-powered Fender will.

That isn't due to the 7591...it is due to the circuit around it not driving them enough. The 7591 is a sensitive power tube and it is easy to overdrive them, yet most of the Ampeg stuff that used them is very clean because they didn't drive them hard enough. 7591's can be made to sound fantastic in a guitar amp.

Greg

[Baxtercat]

Cap'n Juan: neat to see an Audio Guild.

I found one up here in Aptos about 15 or 20 years ago.

I played it around town in No SD County for a while....really liked it. I remember it had an extra 'chamber' in the cab [since some models had another speaker], a wonderful tremelo, and those softer 'toney' 7591s.

I eventually sold it down in Escondido, where I lived then.

[R.G.]

The 7591 was a late-design tube, intended for more compact hifi equipment, which it was designed into, the biggest user being Fisher.

It has the power abilities (mostly) of 6L6, at least the smaller-envelope ones, and a high transconductance/sensitivity. Nice tube.

There is a gotcha. There were never a lot of these made, as the solid state revolution happened before they could ever get cranked up into lots of equipment and fill the service market lines. As a result, they are rare-ish. Worse yet, the Japanese hifi market liked them, and the new/old stock got bought up from the USA in the 70s and 80s. So they're harder to find. The Russian factories made "7591s" which were re-bottled 5881s; lower sensitivity, but it fit the same socket. They do NOT fit the same socket as the other power tubes we normally use.

Be very aware that if you find "NOS" 7591s, they may be counterfeit, or the rebottled 5881s.

Or real. You never know. It could happen, I guess.

[soundmasterg]

Originally Posted by R.G.

The 7591 was a late-design tube, intended for more compact hifi equipment, which it was designed into, the biggest user being Fisher.

It has the power abilities (mostly) of 6L6, at least the smaller-envelope ones, and a high transconductance/sensitivity. Nice tube.

There is a gotcha. There were never a lot of these made, as the solid state revolution happened before they could ever get cranked up into lots of equipment and fill the service market lines. As a result, they are rare-ish. Worse yet, the Japanese hifi market liked them, and the new/old stock got bought up from the USA in the 70s and 80s. So they're harder to find. The Russian factories made "7591s" which were re-bottled 5881s; lower sensitivity, but it fit the same socket. They do NOT fit the same socket as the other power tubes we normally use.

Be very aware that if you find "NOS" 7591s, they may be counterfeit, or the rebottled 5881s.

Or real. You never know. It could happen, I guess.

I haven't tried them yet but EH and JJ both make new 7591's that are supposed to have the same specs as vintage, with the caveat that the EH bottle is bigger than vintage which may cause it to not fit in some equipment.

I heard somewhere....maybe it was VTV....that at some point RCA took a whole warehouse of 7591A's and dumpstered them....since they were a cheap tube back in the day and the solid state revolution was in full swing, and this did a lot to make the prices go up.

Greg

[R.G.]

Originally Posted by soundmasterg

I haven't tried them yet but EH and JJ both make new 7591's that are supposed to have the same specs as vintage, with the caveat that the EH bottle is bigger than vintage which may cause it to not fit in some equipment.

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.

[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]

Originally Posted by R.G.

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]

Originally Posted by R.G.

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.