Current Production 7591As

[Ted]

Do any of the current production 7591As actually comply with the original data sheet?

I've just tried a pair of Harma branded valves, which looked very much like button base 5881s.

Their bias point in a cathode biased 64 Ampeg Reverbrocket was about 30V - a good few volts higher than NOS.

[edit]

Just realised I should have put this in Tubes, b ut can't seem to delete...

[imaradiostar]

Harma is a relabeler if I'm not mistaken.

If they look like button base 5881's they're likely the Russian made 7591A. I've used a pair for MANY years. Mine test very close to datasheet values for cathode bias and regardless of whether or not they sound like "real" 7591's they sound excellent and have given a hard 5 or more years of use, at least a day a week for several hours at a time. They're biased pretty hot in a small amp that gets used with a THD Hotplate every time I plug it in. Only recently have they started to sound ratty and I'm considering purchasing a new set.

In my experience it may be helpful to adjust the cathode resistor to get them to idle at a current you're comfortable with. They may not be identical in that regard but I'd imagine different golder era US 7591's were similar that way.

Here's an endorsement for them- the aforementioned amp was on an old Bogen chassis that I've used for prototyping since 1998. When I built the 7591 amp I liked them so much that I put the amp in a crappy head cab and haven't built a new prototype with it since then. One of these days I'll transfer the circuit to a proper turret board and chassis but I'd have to stop playing it first!

Jamie

[tubeswell]

If you're talking about these:



They do look exactly like Russian 6P3Se from the outside (except for the 'fine print' on the label )

[Steve Conner]

Well, to be utterly pedantic about it, the 6P3SE has two large oval holes in the plate, the tube shown has three smaller round ones.

[tubeswell]

Well just for that I'm gonna delve into my stash of 6P3Ses and see ;-)

[EFK]

Those russian 6p3s tubes have a standard 6l6 type pinout. In fact, I think I remember reading somewhere about people using them as replacements for 5881 and 6l6gb type tubes. The 7591 has a completely different pinout, so I can't see them being interchangeable. I know JJ makes a true 7591 tube, although lately I've been having some issues with them when driven hard. Going to give the EH a try next (or maybe try to find the russian surplus they're probably based on! hahahaha)

[imaradiostar]

I'm sure we'll find people that disagree but I believe the EH 7591 is a modern design, not a relabeled and repinned Russian design. Mine do not act like 6L6's at all- with 400+ volts on the plates they require very little grid bias, probably about half of what 6L6's require. I can't say if they're exactly the same as true 7591's but for musical instrument use they're quite good.

I believe Mike Matthews was answering the need for 7591's by producing them in his Russian factory!

Jamie

[Steve Conner]

Yes, a true 7591 has higher transconductance than a 6P3SE or 6L6GC or even an EL34. This means very close tolerances on the cathode and control grid, so extra care in manufacture. You won't find any Russian surplus tube that matches it.

[tubeswell]

You won't find any Russian surplus tube that matches it.

What about a New Sensor tube? (LoL)

[soundmasterg]

The 7868 is supposed to have the same electrical characteristics as the 7591, and the EH 7868 sounds as good or better than the vintage 7868 and holds up well, so maybe the EH 7591 is also a good tube and vintage correct? I haven't tried them yet myself. I do know that they come in a non vintage correct larger bottle so they won't fit in many old hi fi's.

Greg

[jrfrond]

I can honestly say that the EH 7591A just SUCKS in terms of tone and response as compared to the originals. "Lifeless" is the best way to put it. If you want something that is much closer to the tone of the original, use the JJ 7591S.

The EH is just a repinned three-hole 6L6, NOT a 6P3SE. The JJ is a true power-pentode, not a beam-tetrode, so the characteristics are totally different. I object to this almost as much as I used to object to 6CA7's being called American EL34's. NOT even close, except for the bias voltage requirement.

[imaradiostar]

I can honestly say that the EH 7591A just SUCKS in terms of tone and response as compared to the originals. "Lifeless" is the best way to put it. If you want something that is much closer to the tone of the original, use the JJ 7591S.

The EH is just a repinned three-hole 6L6, NOT a 6P3SE. The JJ is a true power-pentode, not a beam-tetrode, so the characteristics are totally different. I object to this almost as much as I used to object to 6CA7's being called American EL34's. NOT even close, except for the bias voltage requirement.

It makes me sad to hear that. I've always thought mine sounded quite good and my Nashville studio engineer friends agreed. I wonder what I'm missing!

Jamie

[imaradiostar]

I can honestly say that the EH 7591A just SUCKS in terms of tone and response as compared to the originals. "Lifeless" is the best way to put it. If you want something that is much closer to the tone of the original, use the JJ 7591S.

The EH is just a repinned three-hole 6L6, NOT a 6P3SE. The JJ is a true power-pentode, not a beam-tetrode, so the characteristics are totally different. I object to this almost as much as I used to object to 6CA7's being called American EL34's. NOT even close, except for the bias voltage requirement.

Wait, I'm confused. Are you saying they're BOTH wrong- EH being a 6l6 derivative and JJ actually being a pentode?

And furthermore you're saying the EH sounds like crap while the JJ sounds decent even though it's not a beam power tube?

Jamie

[soundmasterg]

I can honestly say that the EH 7591A just SUCKS in terms of tone and response as compared to the originals. "Lifeless" is the best way to put it. If you want something that is much closer to the tone of the original, use the JJ 7591S.

The EH is just a repinned three-hole 6L6, NOT a 6P3SE. The JJ is a true power-pentode, not a beam-tetrode, so the characteristics are totally different. I object to this almost as much as I used to object to 6CA7's being called American EL34's. NOT even close, except for the bias voltage requirement.

Thats interesting because EH's 7868 sounds as good or better than the vintage ones, and they seem to hold up well. I've been using a quad in my main amp for quite awhile now with no issues. The 7868 is supposed to be electrically the same as the 7591, at least with vintage examples. I have some JJ 7591S's here that I have not tried yet, but will at some point. I also have some vintage ones to compare them with. I don't have any of the EH 7591's, but I will probably get some to compare with the others at some point.

Greg