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]

Parallel tubes

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]

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]

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 I think the target application for the 7591 was integrated Hi-Fi amps where it frequently superseded the EL84/7189 in amps by H.H. Scott, Sherwood, Fisher, etc...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]

7591 heaven

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]

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]

7591

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]

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]

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]

Audio Guild

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]

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.]

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.