6L6 vs. 5881 in a Fender-style amp

[solderstain]

Requesting input from the collective here...

For all the Fender-style builds and tweaks I've done since 1979 or so, I've never done anything with 5881s. I'm fortunate enough to have multiple friends with real, original late-50s tweed Bassmans, and I can see why they're so well-thought of.

I have both a '66 Bassman (output stage converted to AA864), and a Pro Reverb that I converted to a 2x12 Bassman 'combo'. I love them both.

Right now, I'm using Philips JAN 6L6GC tubes in the power section of both amps. I'm a 'rock' guy - I suck as a blues player - so those tubes sound great to my ears. I play through British-style speakers versus Jensens or clones there-of.

Since I can never seem to leave well-enough alone, and member 'hired hand's' thread got me thinking about the early Bassman circuit again, I'm starting to think about popping a set of 5881s into one of them as an experiment.

Questions:

Are 6L6s and 5881s different enough that I'd hear a difference? I haven't made any kind of formal study about it, but I've kind-of related to 6L6s as just a higher-voltage 5881 (and vice verse). Is that a mistake?

I can't say exactly why, but since I think of 5881s as low-voltage 6L6s, I worry that the voltages in my Bassman(s) will be too much for 5881s. What kind of voltages can modern 5881s take safely? The plate voltages of the power tubes in the two amps is 420vdc and 436vdc, respectively, when properly biased with a Variac-set 120vac input. Will that cook modern 5881s?

Or are these tubes basically the same thing and the change isn't worth the bother?

[Structo]

Yeah not sure about that, my data shows the 6L6GC has a max plate voltage of 500 while 5881 is 360.

30 watts for the 6L6GC and 23 for the 5881.

In looking over the other specs, there are some differences but the one that sticks out is that VaMax and the Vg2 of the 5881 is only 270v.

Don't know nothing about current produced ones.

[solderstain]

Yeah not sure about that, my data shows the 6L6GC has a max plate voltage of 500 while 5881 is 360.

That's kinda what I've seen too, but if you look at the commonly-available schemo for the 5F6-A, it shows approx. 430vdc on the plates of the 5881s. One of these days, I'm going to take my DMM with me when I visit my local friend who has an original, and see if he'll let me do an anal probe on his amp and see what it's ACTUALLY getting on the plates.

[Structo]

From what I have read and seen, Leo was kind of infamous for applying plate voltages way over spec.

Perhaps he knew that the power tubes of the day were more robust than their specs showed.

After reading several books about the man, he didn't like failures of any kind so it would seem that he did not take risks as far as his amps went.

But like you said or asked, can current production tubes take the heat, so to speak?

[jjman]

I've read that the Sovtek "5881"s are not made to 5881 specs. I believe this since my friend had a set in his 700volt Music Man Bass head with no problems. I'm not sure if 5881s were supposed to be "better" than 6L6 in some way, were "European versions" of 6L6, or something else.

Many tubes are run over specs in guitar amps but it sounds like a real 6L6 has more stamina than a real 5881 regarding higher voltages. At least on paper. As mentioned, looks like the 5F6/6-A Bassman ran them around 425v or so.

Some googlin is probably in order ......

[solderstain]

Some googlin is probably in order ......

Thanks for the responses - I've done some Google work already. There's no such thing as too much information, and I hold the knowledge base here in high regard, so I'm hoping there might be someone here who is already successfully running 5881s at 425v+/-.

Or... someone who's tried both and says 'eh, don't bother'.

[paulster]

I've got a 5E8A build that runs just about 450V on the plates with both rectifiers in and my high (248V versus nominal 240V) daytime wall voltage using 5881s.

I've got resissue Tung-Sols in at the moment and I've had NOS Tung-Sols and RCAs in there with no problems.

I'm a bit weary of the plate voltage which is why I stick to the reissues and keep the NOS tubes for other builds but they're holding up nicely and sound great.

I definitely like 5881s over 6L6s for a Tweed kind of build. 6L6 I'd use in a higher gain scenario when the preamp's doing most of the work and you want a really clean output stage.

[doveman]

Tung-Sol 5881s are running in my rig at 445v and they are fine. Brown Note guys suggested them. They break up a little earlier and don't have quite as much headroom. They seem to be in between the 6V6 and the 6L6 on just about everything. Since my D'lite 22/33 can run all three ... I have tried them all. The 5881s run about 25w in my rig set on the 6L6 setting.

They are the best of the three tubes for me.

The Tung-Sol site shows a lower recommendation but others with experience turned me on to them and they worked great.

The "Crank It Up" tune at my Soundclick site below is with the 5881s if you want a reference.

I had been running 6L6s with my band recently but since I got an EVM12L (more efficient speaker) I have put the 5881s back in.

[solderstain]

Thanks, paulster and doveman - that's the kind of stuff I was hoping to hear. I guess I've got nothing to lose by trying a set of the RI TungSols, since they handle the voltages okay.

Thanks, guys!

[rfgordon]

Originally, there were differences between 6L6 and 5881 tubes. The 5881 was a bit more of a high fidelity tube to start. Often, over the production span of tubes, their characteristics changed, but the published data sheets did not. Some tubes had nomenclature changes, like 6L6 to 6L6G to 6L6GB, etc, and there were different data sheets published as manufacturers introduced new variations. For example, I have some late WWII 6L6 steel bottle tubes, and if you look up a plain 6L6 data sheet, you'll see they want substantially less plate voltage than those produced in the 1950s.

The 5881 did change, but without nomenclature change. I've seen lots of blackface Fenders in which NOS 5881s were quite happy, and sounding great.

In modern production, however, I do not believe there is any difference, other than ink on the glass, between a 6L6 and a 5881.

[doveman]

I have both the Tung-Sol 5881 and the Tung-Sol 6L6GC STR and they are totally different. I think the 5881 may match one of the lower power versions of the 6L6.

The 5881s break up sooner, have less power, less headroom ... I really like the 5881 set better ... the 6L6 are louder and tighter.

So maybe it depends on the 6L6 in question ... seems like I read once that the 5881 reissue is somewhere close to the 6L6GB.

But it's a sweet tube ... my favorite.

[solderstain]

The 5881s break up sooner, have less power, less headroom ...

Hmm... with the stuff being shared here in the last few posts, I'm beginning to wonder if I'll hear much difference with 5881s, compared the the Philips JAN 6L6GCs I'm using now.

I got my first set of these Philips JAN 6L6GCs in a big-box-o-tubes that was gifted to me by a friend. I'd never used them before so I put them in my '66 (modded) Bassman. LOVE THEM! So I started poking around the 'net and bought two more sets.

A couple of the Google hits I got on the Philips tubes described them almost exactly the same way that doveman described his 5881s in the quote above.

Maybe my current tubes are too close to 5881s to make it worth bothering. Only one way to tell, I guess.

[doveman]

You got my curiosity up. I did a bit of research and seemed to find that the Tung-Sol 5881 Reissue that I'm using is closest to the 6L6WGB 25w tube.

I think all of the 6L6GC types are 30w tubes with a bit more power and headroom.

While I found this is several places, I usually buy my tubes at TheTubeStore and I think they have a pretty good description (attached link) of 6L6 types. But for $40 a set, these 5881s are pretty nice.

http://thetubestore.com/6l6templeton.html

[6G6]

The whole point of the 5881 was to produce a "MilSpec" 6L6, that could run continuously for days, without fear of failure, even with vibration, heat, etc. ( Think radio, in a tank.)
They were also used in industrial applications. (Motor controllers, etc.)
They were built better, with the best materials, but also speced to run lower voltages.

I have run original Tung Sol 5881s in my Bassman at 450-460 volts for years with no problems.
Yes, it was more voltage than the specs call out.
It wasn't continuous for days on end, though.

They should give you something between a 6V6 and a 6L6, with greater longivity.
400- 450V ,should work out just fine for you.

[solderstain]

Thanks, doveman - I've been to the Tube Store and seen most of the online references. I think we all pretty much take for granted that tube builders play a little fast and loose with adherence to 'specs'.

And even if all 6L6GCs and all 5881s were directly 'on-spec', I'm not sure that I'd honestly hear the difference between a 30w and a 25w tube. But as I say, there's only one way to tell.

One of these days, I gotta learn to leave well-enough alone...