New Tung Sol 7581a power tubes

[pfschim]

well, at least new to me

I have a Fender Studio Bass amp that uses a sextet (2x3) of 6L6's. I have the NOS Sylvania/RCA 6L6GC's that came with the amp when I bought it (a whole additional score in that transaction), and I currently running a set of Ruby 6L6GG-STR's in it now - which sound fine.

A fellow TBer johnk_10 did a restore on another Fender Super Twin amp (basically the same amp as the Studio Bass) and had some NOS 7581A's (pretty rare) that he put in it. He reported very good results with these tubes over the originals and felt they gave the amp a bit more headroom (which makes sense). The original 6L6GC's have a plate dissipation of 30W (giving the amp about 180w). I understand that "real" 7581A's are completely compatible in amps designed for 6L6 power tubes, but they are rated at a plate dissipation of 35w, which would push an amp with 6 of them to a bit over 200w. Not a huge deal, but I remain interested in the idea.

I have been looking around for NOS 7581A's, and have found them on occasion, but usually at very lofty prices.
I recently saw that the Tube Store is showing a Tung Sol 7581a (www.thetubestore.com - Tung-Sol 7581A Audio Tubes new production, that advertises 35w plate dissipation - not a 7581 at 30w as I have seen in the past. This got my attention as the price is shown as $29 per tube (for reference the NOS 7581A's I have seen are all in the $89-100+ per range).

If the new production Tung Sols are truly a 7581A design at that price point, I will probably go ahead and get six and try them out. But I'm wary of new production tubes with specs that may be a bit questionable.

Anyone have a point of view that they would share on this topic ?

 

[pfschim]

hey, a topic on TB that no one has an opinion or POV on.
a first ?

 

[beans-on-toast]

It's an interesting tube. No question that the original is a good 6L6GC substitute. It's a commercial version of that tube, built better.

It might be a good substitute for the 7027A, as used in some older Ampegs, as well.

The problem with so many of the current production tubes is that they are not the same as the originals. In some cases it is a new design. Other times it is something close that they label as a US tube.

It will be interesting to see what people think of these tubes.

 

[B-string]

I suspect the same cage is being used for several "different" types in the line like EH does.

 

[pfschim]

I suspect the same cage is being used for several "different" types in the line like EH does.

Thanks for posting B, I'll take your word on that, but does that mean these are really not 7581A spec tubes ?
As I said in the OP, this is really not a huge deal for me, the 6L6GC-STRs I have in the amp now work and sound fine. I just keep remembering johnk_10's comments about the NOS 7581A's he put in his, and when I saw these new Tung Sol's it got me thinking about it all over again.

darn you johnk_10, you and your NOS 7581A's

geez, from the prices they ask for those tubes, you'd think they were made of pure unobtainium by the unstained hands of virgin's or something like that.

 

[pfschim]

It's an interesting tube. No question that the original is a good 6L6GC substitute. It's a commercial version of that tube, built better.

It might be a good substitute for the 7027A, as used in some older Ampegs, as well.

The problem with so many of the current production tubes is that they are not the same as the originals. In some cases it is a new design. Other times it is something close that they label as a US tube.

It will be interesting to see what people think of these tubes.

B0T, they say in the copy that they have the 35w plate dissipation of the original 7581A tubes. In the past I have seen 7581 (not A's) and they seemed to honestly indicate they were just a 6L6 alternative with basically the same 30w plate dissipation. I don't want to sound naive, but it seems like they would not be able to get away with listing specs that were not real .. surely someone would test them and let the world know. right ?

I mostly just don't want to be the proverbial fool, easily parted from his hard earned $$

 

[B-string]

I seriously doubt it is built to 7581A design blueprints. Do I believe it may be a 35 watt plate dissipation tube? Yes, but like EH and JJ I think they are re-bottling. JJ's 7591S for example does not meet plate dissipation, but will fit the same height as the originals where EH's are taller and do not fit physically in many cases but are 35 watt units.

New production is not held to the same standards as when tube manufacture was in its prime. How do you enforce an expired US patent from Soviet block countries anyway?
Be happy they are still manufacturing.

 

[beans-on-toast]

B0T, they say in the copy that they have the 35w plate dissipation of the original 7581A tubes. In the past I have seen 7581 (not A's) and they seemed to honestly indicate they were just a 6L6 alternative with basically the same 30w plate dissipation. I don't want to sound naive, but it seems like they would not be able to get away with listing specs that were not real .. surely someone would test them and let the world know. right ?

I mostly just don't want to be the proverbial fool, easily parted from his hard earned $$

They claim all sorts of things. Reviewers don't perform destructive test on tubes as far as I've seen.

A tube can be run hotter or cooler than the spec. There isn't a magic number. Many NOS tubes could dissipate more than the specs indicated. Fender used to run tubes hard in some amps, above spec. The specs were published based on studies that they did to provide a long service life. Run them a bit over spec and they may not last as long. Some tubes were conservative in their design.

If you look at the metal plates in this tube it is built pretty well. An indication that it may be able to dissipate more heat than a standard 6L6GC.

 

[webmonster]

35w dissapation if true would be good for amps that run 7027a hard at 600+ volts, so I am interested in these.

 

[coreyfyfe]

Probably not many who have tried them personally hence the limited opinions. I know a few people who have used them as substitutes for 7027As in ampeg V4/B24 amps. Not sure how well that's working out long term since a true 7027a would have a higher plate voltage maximum than the 7581a but similar specs otherwise.

 

[beans-on-toast]

I've been doing a bit of digging and have come across some conflicting information.

-Some places rate the plate dissipation of the reissue Tung Sol 7581A at 35W, others at 30W. Note that plate dissipation is not the same as how many watts a tube can put out. It is how much heat the plate can dissipate.

-The data sheets that resellers post with these tubes are a copy of the original 7581A ones from Tung Sol. This comes from New Sensor, they didn't create a new data sheet.

- According to the data sheets, both the Tung Sol 7581A and the JJ 7027 have a maximum plate voltage of 500V. I know that the JJ can take higher voltages. A lot of people use them in their V4B's.

-Looking at the JJ 6L6GC and the JJ 7027 below, they look the same.

- Looking at the image of the Tung Sol 7581A, it has a large beefy plate.

- Below are the JJ 6L6GC, JJ 7027A, Tung Sol reissue 7581A, and NOS GE 7581A/KT66. Also included are data sheets for the JJ7027A and the New Sensor Tung Sol 7581A.

​

 

[Passinwind]

hey, a topic on TB that no one has an opinion or POV on.
a first ?

OK, for starters: read this blog.

One thing to consider in your case is that those amps already run pretty hot, so higher plate dissipation may be good for the tubes but bad for other bits like the transformers.

 

[coreyfyfe]

I've been doing a bit of digging and have come across some conflicting information.

-Some places rate the plate dissipation of the reissue Tung Sol 7581A at 35W, others at 30W. Note that plate dissipation is not the same as how many watts a tube can put out. It is how much heat the plate can dissipate.

Just a guess but this could be because they're marketing both a 7581 and a 7581A and some people may not be properly differentiating between them.

 

[beans-on-toast]

Just a guess but this could be because they're marketing both a 7581 and a 7581A and some people may not be properly differentiating between them.

That interesting. I wonder if the 7581A is a newer revision that they will be selling till the 7581 is gone. That would explain the 30W vs 35W difference in the reseller descriptions.

It is confusing. Often they say 6L6 when they mean 6L6GC.

 

[Passinwind]

That interesting. I wonder if the 7581A is a newer revision that they will be selling till the 7581 is gone.

See post #12. The Google+ post I lifted the link from is dated Feb 2015. Link Removed

 

[coreyfyfe]

OK, for starters: read this blog.

One thing to consider in your case is that those amps already run pretty hot, so higher plate dissipation may be good for the tubes but bad for other bits like the transformers.

That's a pretty solid review, covers the differences in structure/manufacture and even mentions them as a replacement for 7027As in ampegs.

Interesting indeed.

 

[Passinwind]

That's a pretty solid review, covers the differences in structure/manufacture and even mentions them as a replacement for 7027As in ampegs.

Interesting indeed.

Yep. I have a friend just up the street who's a New Sensor dealer and he also has a large NOS stash. I trust him a little more than any online vendor and I'll go have a chat later today, but Doug certainly has a very good reputation too.

 

[beans-on-toast]

Yep. I have a friend just up the street who's a New Sensor dealer and he also has a large NOS stash. I trust him a little more than any online vendor and I'll go have a chat later today, but Doug certainly has a very good reputation too.

I'd be interested in hearing what you conclude once you've talked to him.

This looks like a good alternative to the JJ 7027. It is getting very hard to find a properly matched quad of NOS 7027A's.

 

[coreyfyfe]

I'd be interested in hearing what you conclude once you've talked to him.

This looks like a good alternative to the JJ 7027. It is getting very hard to find a properly matched quad of NOS 7027A's.

Definitely. I picked up two matched quad of sylvannias, one from TC tubes and one from Brent Jessee Audio Tubes, along with a mixed-brand matched set from AES a while back. Each of these purchases cost me about double what a matched quad of these 7581As appears to run. I should be good for a while, but it's nice to have options. I haven't been thrilled with JJ power tubes in general of late, and the sovtek 7027As didn't last long in my V4 for one reason or another.

 

[Passinwind]

I'd be interested in hearing what you conclude once you've talked to him.

This looks like a good alternative to the JJ 7027. It is getting very hard to find a properly matched quad of NOS 7027A's.

My friend has a stellar resume and pretty top notch test equipment, so he can generate and document characteristic curve sets fairly easily. I'm diving back into the tube guitar amp pool pretty deeply at the moment and getting just the right 6L6 variant into my just-rebuilt Fender is on my radar anyway, so hopefully I won't just be a time waster when I go visit. I'm a bit more interested in the softer side, and I've always loved 5881s for that. Many of the same confusing/obnoxious "reissue" labeling issues have existed in that context for many years now, as I'm sure you know.