Power Tubes... Can they cause volume (power) loss as they age?

[Ch0jin]

So I was jamming with a couple of mates the other night, and for the second time (with the same guys) I've been totally drowned out by the other guitarist and drummer. First time I thought I had impedance mismatched my amp and cab (had the amp still on 8 and 16 Ohm cab) but this time I just dragged along the amp with it's built in 12" speaker and same deal.

I'm using a '92 -ish Peavey Ultra 112 (USA Made) which is rated at 60W via a pair of Sovtek 6L6's that have been in there since like '94. The other guitarist was running a racked JMP-1 and 8008 power amp into a Sovtek quad loaded with eminence 12" speakers.

Even with my amp in the corner of the room for maximum amplification, his rig on like "4" swallowed mine whole. I didn't think an 80W solid state power amp would do that, so now I'm wondering if "that sounds about right" or if I should try out some new power tubes.

I have a JTM 45 build "kind of" under way (just yesterday received all my trannies from Marstran) but if 60W cant hack it, the JTM probably wont either.

I've been looking hard at the Ceriatone Yeti in 100W guise as possibly a new jamming amp.

I'd hope I could hold my own over the noise these cats make with a hotrodded 100W plexi (and maybe a 69 basket weave slant cab with 75W Greenbacks. I'm not sure I'd like to throw a 100W plexi into my 1960's era alnico's given I have no idea what their power rating is)

Anyway, thoughts?

I was just a little taken aback, I mean everyone seems to be talking about little amps these days and I'm at jams lying on the ground with my head in front of a speaker trying to hear myself with a dimed 60W amp........

[deeaa*]

60W tube watts should really be plenty. Indeed the tubes may be dying, and with such old tubes I'd definitely change them already rather than risk a catastrophic tube blowout, but it might simply be that the 4x12" yields so much more dB at lower frequencies than your single - not to mention open-back - does that it seems like it's not enough. Closed-back and multiple speakers pump air so much more efficiently. It doesn't need that much extra to sound way overbearing in comparison with a tinny open-back single speaker.

Speaker efficiency after all is way more important for volume than actual wattage. Some 36W like my old Ceria was is quite enough to play along with 100W Marshall rigs when used with a suitable 4x12" with V30's etc. in it that are pretty efficient, but it could hardly be used with a drummer using another 2x12" cab I had.

Also, EQ and gain etc. settings can have a huge impact on volume. Despite I use a 100W tube Marshall head now, my 4x12" isn't the most effective plus my EQ/Gain settings are pretty low, I find that I have to turn the amp past halfway mark to be well heard! I really need to push the lead master volumes to near dimed to really be able to scream over the rest of the band.

So it might also be that you're far from 'unity gain' within the amp structure, i.e. at some point some stage is not feeding full signal to the next stage due to low gain setting or whatever, but I'd first venture it's the cab/speaker inefficiency that is to blame here.

And for devil's sake change those t00bs already :-)

[tunghaichuan***]

It sounds like your power tubes are dying. Loss of volume is a sign that they are on their way out.

Are the Sovteks really 6L6s or are they the 5881s? The Sovtek 5881 isn't a real 6L6 and will put out less power in a circuit designed for a real 6L6, like your Peavey. The Sovtek 5881 needs a different primary impedance on the the primary of the OT and higher plate voltages to produce the same power as a real 6L6.

If they are real spec 6L6s, they are probably on their last legs. Modern production tubes don't last nearly as long as NOS types.

I'd definitely retube with a *real* set of 6L6s, 60W of tube power should bury any 80W ss amp without breaking a sweat. If fact, if you can swing it, you may want to get a set of NOS 6L6s, RCA, Sylvania, and GE are all great. If you can find them, the Sylvania STR-387 and RCA 7581A are excellent choices, but are hard to find and are expensive.

Also change the PI tube. If it is getting weak, it may not be driving your power tubes to full output.

Since the amp is almost 20 years old, I'd check the filter caps in the PS for good measure to make sure the PS can supply necessary current.

In fact, you may want to get the schematic from Peavey and go through it with a scope to see if there isn't some other weirdness going on.

[guitartango]

Solid state amp ----- please do not swear on this forum

[Ch0jin]

Thanks guys, that's pretty much what I was thinking too. I'll sort a new set of toobs and see how I go from there. To answer a few questions...

Are they real 6L6's? I'd always assumed so yeah. At least they are stamped "Sovtek 6L6WXT" and "Made in Russia" Here's a pic..


Clash of the Cold War Rivals I by Ch0jiN, on Flickr

I have the schematic, I repaired some dry jointed filter caps not long ago to fix an intermittent hum problem. I removed and physically inspected the main filter caps and they "looked" fine. I have to recap and older (1970's) Peavey Bass head soon too so maybe I'll tackle both of them.

Nothing sounds particularly "weird" at apartment volume I hadn't noticed anything, it's just when I get it up to 10

Regarding speakers, I totally agree with you Deeaa, however I have tried it with my 4x12 as well and it still sounded wimpy (although I did have the impedance mismatched as I mentioned before)

That said, I have no data on the speakers in my 4x12 other than they were made in the 60's (cause that's when the cab was made) and that they were made locally. They might be horribly inefficient....or not I guess I'll have to A/B the cab with something else at some point.

Here's a pic if your curious..


Fluxing Hi by Ch0jiN, on Flickr

Oh and Tig.... Didn't mean to offend you with my Solid State reference. If it makes you feel better, it wasn't my amp Both my guitar amps have Toobs.

[tunghaichuan***]

Thanks guys, that's pretty much what I was thinking too. I'll sort a new set of toobs and see how I go from there. To answer a few questions...

Are they real 6L6's? I'd always assumed so yeah. At least they are stamped "Sovtek 6L6WXT" and "Made in Russia" Here's a pic..


Clash of the Cold War Rivals I by Ch0jiN, on Flickr

Just as I suspected. Those are 6П3С-EB (In Cyrillic, 6P3S-EV in Latin) tubes. They are rebased Sovtek "5881" tubes. The first 6П3С-EB tubes exported from Russia back in the early 90s had a coin base and were labled "5881." They were nothing like a real Tung-sol 5881. Nor were they like a 6L6GC. Rather they were just similar enough to use in 6L6 circuits. At the time, they were a godsend because GE had shut down their factory in Kentucky and it was the first time a 6L6 type tube wasn't in production since the 1930s. Sovtek then began to have the same tube manufactured with a full-size base (identical to yours) so that the claws in Fender amps could grip them. The coin based tubes didn't fit in Fender amps right. Sovtek relabeled the tube 6L6WXT. The WXT suffix is a tip-off: no real Western-made tube had this suffix, and it is meaningless under the Western tube designation scheme.

The tube is very rugged and long lasting (as the EB/EV suffix denotes). It however does not produce as much power in a 6L6 circuit as a real 6L6. Also, IIRC, you have to bias them really hot to get them to sound good. They require a different impedance to develop full power. The Sovtek amps that use these as the stock tube have both the right OT and very high B+ levels to get them to develop full power.

I ran an experiment with two of my samples (I have a matched quad of the identical tube.) I have a Champ-style circuit that has beefed up transformers so that I can run bigger power tubes. I've run a 6550, EL34 and 6L6s in it. I tried two of my Sovtek 6L6WXT tubes in it and biased the amp to 40W dissipation in Class A. One tube had a hint of red-plating, the other the other none at all. So it's not really a mini 6550, but the 6П3С-EB will take a lot of abuse that would kill a real 6L6GC very fast.

Luckily, there are some real 6L6GC spec tubes being produced today. However, none are particularly robust, or long lasting as NOS/Western. I would bet that your amp was designed for the Western 6L6GC style tube, knowing Peavey.

[Tig***]

Just as I suspected. Those are 6П3С-EB (In Cyrillic, 6P3S-EV in Latin) tubes. They are rebased Sovtek "5881" tubes. The first 6П3С-EB tubes exported from Russia back in the early 90s had a coin base and were labled "5881." They were nothing like a real Tung-sol 5881. Nor were they like a 6L6GC. Rather they were just similar enough to use in 6L6 circuits. At the time, they were a godsend because GE had shut down their factory in Kentucky and it was the first time a 6L6 type tube wasn't in production since the 1930s. Sovtek then began to have the same tube manufactured with a full-size base (identical to yours) so that the claws in Fender amps could grip them. The coin based tubes didn't fit in Fender amps right. Sovtek relabeled the tube 6L6WXT. The WXT suffix is a tip-off: no real Western-made tube had this suffix, and it is meaningless under the Western tube designation scheme...

Wow!

[Ch0jin]

Yeah wow is right! Thanks heaps Tung! I have no idea what the original tubes were (apart from the fact they were 6L6's), as I didn't really check before they died and were replaced with those Sovteks by the store.

If I can ask another question

How do I avoid buying 5881's labelled as 6L6's?

I wasn't planning on going NOS as I was going to save that cash for the tubes in the JTM45 I'm building. Aside from the suggestions you have already offered, I've heard JJ's sound good in this amp (all the way through). Any thoughts?

And thanks again for the read. I'm amazed you got all that from my pic which was designed to be more "arty" than "informative"

[tunghaichuan***]

Yeah wow is right! Thanks heaps Tung! I have no idea what the original tubes were (apart from the fact they were 6L6's), as I didn't really check before they died and were replaced with those Sovteks by the store.

If I can ask another question

How do I avoid buying 5881's labelled as 6L6's?

I wasn't planning on going NOS as I was going to save that cash for the tubes in the JTM45 I'm building. Aside from the suggestions you have already offered, I've heard JJ's sound good in this amp (all the way through). Any thoughts?

And thanks again for the read. I'm amazed you got all that from my pic which was designed to be more "arty" than "informative"

I don't know much about the history of Peavey amps, but I've heard of them coming with real NOS Sylvania 6L6GCs.

It's hard to navigate tube nomenclature these days. Back in the good old days, if you bought a tube that said 6L6GC on it, it was a real 6L6GC spec'd tube. Now we have to deal with a lot of marketing BS and misdirection.

Obviously, I'd avoid anything that was labeled 5881. The Sovtek tube isn't even in the 6L6 family, and a real 5881 is only good for 23W vs 30W for a 6L6GC. I'd also avoid any of the Sovtek tubes in general.

If you look at this page:

http://thetubestore.com/6l65881types.html

The JJ, Winged C, and Svetlana are all real 6L6GC tubes. Not sure about the others. You'd also want to stay away from the 6L6GB as it is only a 23W tube like the real 5881.

I happen to like JJ tubes, love their EL84s, but have not tried their 6L6s. It looks like a real 6L6GC rated tube, so you may want to give it a try. I'd look for a vendor that does extensive testing and has a good return policy. Be aware that nothing made today will last nearly as long as NOS tubes will, so you will have to replace them more often.

Oh yeah, stay away from the run-of-the-mil 6П3С tubes. With out the -EB/EV on the end, it is a very different tube. The EV/EB tube is a ruggedized tube good for 10,000 hours according to the suffix. Without the suffix, the tube is a weak-*** 6L6-like tube. Probably equivalent to the 6L6-G, and only good for about 19W. Groove tubes used to relabel this as a 6V6 back in the 90s when there weren't any 6V6s being made.



The tube on the right is the 6П3С. The one in the middle is the 6П3С-EB aka Sovtek "5881."

Here's an even better picture of the 6П3С



You can see the designation marked on the tube. Avoid these at all costs.

Good luck and let us know how it all shakes out.

[Ch0jin]

Thanks heaps Tung! You sure know your tubes!

[Ch0jin]

Quick update....

I now have a matched pair of SED Winged C 6L6GC's (none of this puny 5881 stuff, thanks again Tung) and a little pile of Tung Sol and Shuguang 12AX7's on there way to me. I even snuck a cheap NOS 12AU7 in there to try out. The Peavey Ultra is a massive gain machine so I figured the lower gain tube might be fun to try, especially considering NOS 12AU7's are WAY cheaper than NOS 12AX7's.

The Chinese Shuguang was chosen not for this amp, but for my JTM45 build, as I've read a number of horror stories about Russian tubes not hacking it in cathode follower circuits (V2 in a JTM45). Luckily the Peavey doesn't use a cathode follower so I can try anything I like in that puppy.

The horribly distressing side story is, last week I was bidding on a pile of (40) NOS 9pin tubes including 15 or so 12AX7's (including Phillips Miniwatt Mullard and all sorts of tasty treats) from a guy in the middle of nowhere in Tasmania. My winning bid up until literally the last second (I was frantically typing in numbers and pressing enter) was $38. Yup. The lot went for like $49. I then checked out prices of English made Miniwatt tubes... around $130 a pop.....

To add insult to injury, I dug out some old 12AX7's that I deemed "dead" 12 or so years ago when I ripped them from an old 60's head and low and behold, 3 English made Miniwatt 12AX7's. Seems they were pretty popular over here back in the day. Needless to say, even though I don't have a tube tester, I do plan to drop them into an amp at some point and double check they are indeed "dead".
.
Sigh..... I could have turned over that pile of tubes for enough cash to buy a couple of whole amps.

Anyway, considering the shipping option from thetubestore was the ultra expensive $70 express service, I should have them by next week. Probably before I receive the tube bases I just ordered to make a bias probe doohicky, so I'll probably just drop them in and see what happens and then check the bias later (amp is fixed bias and designed for 6L6GC, so unless the guy who replaced the original tubes with the Sovteks changed the bias resistor, I reckon I should be in the ball park anyway.)

[Spudman***]

I'm interested in hearing what you think of those 6L6s. I've had 5881s in my Hot Rod Deluxe for a while and want to change back to 6L6.

[Ch0jin]

No problems Spud I'll post up how it all goes when they arrive. I can say that up until recently when the amp just lost all it's grunt, I was pretty happy with the 5881 style tubes I had in there. I have a recording of the amp pretty much dimed on the "crunch" channel that we made in the rehearsal room, just some blues wankery, but to my ears it sounds pretty tasty with the drums and bass. I'd be happy if I could recreate that sound with a bit more power behind it, and I'm thinking going back to the 6L6GC the amp was built for will help me do that. I'm also keen to try and change the sound of the "Ultra" channel too. Being from the same linage as the 5150, the amp has gain for days, but the Ultra channel always sounded a bit "fizzy" to me.

[NWBasser]

Just to add a bit here, if new tubes still doesn't generate enough volume, I'd be looking to add speakers to the equation.

IMO, speakers are a larger part of the volume equation than watts. If the other guy is using a 4x12, that will make a lot of sound to compete with.

[Edit] Oops, a bit tired today. I now see that Deea has already posted a much better speaker discussion than I just did.

[Commodore 64***]

Just another reinforcement of my belief that Tung may be God.

I'm having a hell of a time getting a 12AX7 and 12AY7 that aren't microphonic for my 5E3. I'm actually considering NOS.

[tunghaichuan***]

Just another reinforcement of my belief that Tung may be God.

Hardly. I would bet that Ch0jin has forgotten more about electronics than I'll ever know. I've just been doing this a long time and am OCD/pedantic about minute details.

I'm having a hell of a time getting a 12AX7 and 12AY7 that aren't microphonic for my 5E3. I'm actually considering NOS.

FWIW, I suspect a lot of new production 12AY7s are nothing more than weak-testing 12AX7s. NOS might be your best bet. Look for 6072 tubes, they are industrial-labeled 12AY7s. They'll probably outlast new production tubes by a great deal, and will probably sound better as well. If you find 6072 tubes, be prepared for sticker shock.

[Ch0jin]

[QUOTE=tunghaichuan;221122]Hardly. I would bet that Ch0jin has forgotten more about electronics than I'll ever know. I've just been doing this a long time and am OCD/pedantic about minute details.

Aww shucks, thanks for that Tung.

The reality is that vacuum tube technology (aside from CRT's) was off the syllabus by the time I studied electronics. All I've learned has been from the older guys I worked with like 15-20 years ago, and recently, from the intrawebs.

You could say I was raised "Solid State" and converted to "Vacuum Tube" in my late 20's.

Just received my package from thetubestore ! Man, $70 shipping really does make those couriers hustle. From Ontario to Sydney in 5 days. That's got to be the fastest I've ever received anything from that far away

Now I just have to wait out the rest of today at work.... (or perhaps a few more days until I build a bias adapter so I can see how the new tubes bias up. Working in a 1 Ohm resistor inside the chassis looks far too much effort. PCB's huh.)

[Commodore 64***]

Yes, I 'd be remiss if I didn't mention Chojin too. Luckily, there room for multiple deities in my tube worship

[tunghaichuan***]

Yes, I 'd be remiss if I didn't mention Chojin too. Luckily, there room for multiple deities in my tube worship

It's just a matter of keeping at it and asking questions. If I can learn this stuff, anybody can. I don't come from a technical background, so it was a pretty steep learning curve. And I'm mostly self taught, but I was lucky: I found a local pro amp builder who showed me some stuff that wouldn't have occurred to me otherwise.

Finally there are a bunch of good technical forums to learn from. Don't be afraid to ask questions. Lots of the posters enjoy helping others with their various questions.