Modern EL34 reliability?

[g1]

Sovtek EL34G's were not very good back in the day and they are likely just as bad now.

This was my experience as well.
Perhaps one of the options for troublesome EL34 amps that should be considered is conversion to 6L6, like Marshall had to do in the 90's.
(this would be for those who do not want to spring for real NOS, which I guess I would consider pre-90s)

As far as the discussion about why modern tubes seem so crappy, I will add my pet theory about so many amps modded to adjustable bias; and then adjusted hotter to meet some mythical % figure because the designers didn't have a clue what they were doing with their cold bias.

[bob p]

This was my experience as well.
Perhaps one of the options for troublesome EL34 amps that should be considered is conversion to 6L6, like Marshall had to do in the 90's...

I remember EL34 always being less robust in Marshalls than KT66, KT88 & 6550. Hasn't that always been the case? Isn't that just the beam tetrode vs. pentode thing all over again?

As far as the discussion about why modern tubes seem so crappy, I will add my pet theory about so many amps modded to adjustable bias; and then adjusted hotter to meet some mythical % figure because the designers didn't have a clue what they were doing with their cold bias.

^ Agreed! But I don't think it's really a pet theory. I think your pet theory is FACT.

Modding amps to provide adjustable bias is a definite contributor to the problem. Manufacturers like to bias their amps cold for reliability reasons; they know exactly what they're doing. The standard recipe is to provide cold bias, and maybe balance adjustment. IME under these sorts of operating conditions tubes DO last. But bias them hot and you're intentionally trading away tube life in exchange for tone; it should not be too surprising when tubes burn out. The brightest candle burns out fastest, as they say.

I think that attenuators are another contributor to the problem. Sure, we all like the cranked plexi tone, but very few of us can get away with cranking a plexi into a full stack to get that tone. I'm willing to bet that if we all ran plexis directly into full stacks, then tube lifespan would be prolonged significantly, as the Bleeding Ear Syndrome amounts to a feedback loop that makes us turn down the volume, which in turn prolongs tube life. If you stick an attenuator in between the amp and the cab, things change dramatically.

Ramble:

I don't remember attenuators being all that popular until fairly recently (but then my frame of reference spans several decades.)

I remember when Tom Scholz was one of the first guys to champion their use, and he had to design his own attenuator because there was no option commercially available at the time. He started manufacturing and selling the Power Soak but it wasn't all that common. Marshall Power Brakes, THD Hotplates and TW Airbrakes came along, but their price tended to limit how many people deployed them. We didn't hear as many complaints about tube failures as we hear now, at least partly because attenuator use wasn't all that common in the old days as it is today.

Before Ken Fisher passed on, those of us who knew how he built the Airbrakes were honor bound not to openly publish the information. In the 1990s Kelley had drawn up an Airbrake schematic in OrCAD and that PDF was circulated among a select few Ampagers. (that schematic had a mistake intentionally drawn into it, as sort of a safeguard just in case it got loose.)

What amazed me was that as soon as Ken Fisher died, a few people started making claims about being his collaborator, or his ghost builder, at a time when it became impossible to corroborate or refute those assertions. Some people seemed to be trying to grab a little piece of Ken's coattails to ride on by claiming that they secretly built his amps for him. But I'm digressing.

Back to the tube problem -- prior to Ken's death the Airbrake, like the other attenuators, was not at all common. It was a costly boutique item and very few people had one. At the time of Ken's death it seems that everyone's respect for his intellectual property rights (and the interests of his estate/surviving family members) went right into the trashcan. Although people here still respected Ken's estate and never disseminated the Airbrake schematic, someone released a layout diagram of the Airbrake (I think it was at the Amp Garage). Because the Airbrake was a simple design with a low parts count, everyone and their brother suddenly had cheap access to a high quality attenuator. DIY types started building Airbrake clones en masse.

That was a watershed event. There's not a guy alive at the Amp Garage who has built a TW clone who hasn't also built an Airbrake.

Today adjustable bias and attenuation are ubiquitous. We're seeing lots of hot-rodded high-gain amps that are being run with HOT BIAS into RESISTIVE LOADS. That's a deadly combination for tubes. And everyone is doing it. Maybe the reason that EL34 are getting such a bad rap today is that people just aren't being very kind to them, and because being pentodes they're just not as robust as beams.

It's a sad truth that hot bias and attenuators tend to drive tube consumption in the marketplace. That's going to result in the consumption of a lot of new production tubes, and it's also going to prematurely deplete the supply of NOS tubes from the market. If anyone thinks NOS tubes are too expensive now, just wait ... it'll only get worse. In some respects I think attenuators may be our own worst enemy.

[drewl]

I haven't had as much bad luck with my EL34's.

Guess I better keep my original Mullards, Svetlana's etc. For my own personal use.

I've run my old Marshalls into a Hotplate since THD first made them, and even made my own crude attenuators before the internet and never had any problems.

Those amps don't even have screen resistors.

[Justin Thomas]

I'd also like to see where we end up with attenuators, hot bias, and ANY power tubes... now there are guys screaming for an attenuator in their 5W amp because it's still too loud. We're not only going to be using our supplies of "Big Bottles," but small bottles as well...

It's one thing to use one or two steps to suit a venue, but when we're expecting to be able to use a 100W amp in every venue from a stadium to our bedroom, we're a little lost. Personally, I HATE the sound of modelers and software and silent anything. So I wait until the time comes to crank it up, and I enjoy the hell out of it. But I'm not going to run my Bassman into an attenuator for silent playing - bad for the amp, bad for my tone.

It's also all a lesson in learning to appreciate many different sizes and topologies of amps.

Anyway, not sure where 'm going with all my philosophizing...

Justin

[tubeswell]

This amp I'm working on at present (a 1959 RI plexi 100 handwired in the UK in 2005) has a B+ around 500, with screens a couple of volts below that. I noticed this morning that the AC-limiting resistor for the bias winding is 27k (and that this is what the reissue schematic shows for that amp). But there is a notation on the 1970 'unicorn' schematic for the 1959 100W showing 22k (bracketed beside the 27k) for this resistor. So I'm going to cite historical precent (to the owner who doesn't want his amp modded), and I shoved a 22k in there and hey presto, the bias voltage range is now -43.6 to -54 (instead of -32 to -42).

I'm also figuring out how I can mod the amp to lower the screen voltage without the owner being any the wiser. My 1st thought is to change the screen supply wire from the choke side of the power rail to the middle of the screen filter cap stack. The VDC there is 248 unloaded. If that's not high enough, I was going to replace the 56k balancing resistor on that bottom filter cap to something like 270k, which would bring that node to around 420V. (or 100k which would give around 330V). What would you do?

[Enzo]

I got opinions, but can't say they are facts. I think attenuators came about as a result of the Led Zeppelin era. Jimi. Whatever. In those days three 100 watt MArshalls stacked each on two 4x12s was your basic stage rig. Hell, even our band had to compete with a guitar through a 100 watt and two 412s. "Hey, turn that down" everywhere we went. SO everyone wants that cranked to the sky sound, so the attenuator is born.

Adjustable bias. Peavey even spelled it out for us. They design them cool for reliability and long tube life. The tone is in the preamp. In the guitar world "bias" has taken on mythical qualities. I had a guy come in with some small amp, I think a Classic 30, and wanted me to modify it for adjustable bias. it wasn;t because he wanted to tinker, but he had been told you MUST adjust the bias every time you change tubes. SO he couldn't do that for his new tubes unless we did the mod. Players came to expect and demand bias controls, back to Peavey: they started adding bias controls, but they are very limited in range, so you could turn it end to end and still not underbias the thing. But at least ther was a knob to twiddle. Wherever 70% came from it is now religion. So yes indeed, they crank it up to the sky. "Wow, my amp sounded the best ever, right up to when the tubes melted."

[g1]

I think that attenuators are another contributor to the problem. Sure, we all like the cranked plexi tone, but very few of us can get away with cranking a plexi into a full stack to get that tone. I'm willing to bet that if we all ran plexis directly into full stacks, then tube lifespan would be prolonged significantly, as the Bleeding Ear Syndrome amounts to a feedback loop that makes us turn down the volume, which in turn prolongs tube life. If you stick an attenuator in between the amp and the cab, things change dramatically.

Good point, watt/hours are something there should be an onboard counter for. Imagine if the player could see the meter ticking for the cranked into attenuator amp compared to a master volume type amp putting out the same speaker loudness.
'Player' forums are full of guys asking 'how do I get that cranked tone?' and are always presented with the various attenuator options.
But there is a new game in town. Stepped PPIMV switches with settings actually labelled in watts. Most guys on 'player' forums seem to believe there are actually big power attenuators built into the amps, which is not the case.
So the users can't seem to hear the difference to real attenuators, and the manufacturers are saving tube life. Win/win.

[Dave H]

I'm also figuring out how I can mod the amp to lower the screen voltage without the owner being any the wiser. My 1st thought is to change the screen supply wire from the choke side of the power rail to the middle of the screen filter cap stack. The VDC there is 248 unloaded. If that's not high enough, I was going to replace the 56k balancing resistor on that bottom filter cap to something like 270k, which would bring that node to around 420V. (or 100k which would give around 330V). What would you do?

The supply resistance at the junction of the two 56k balancing resistors will be 28k. Won't the screen current pull the voltage down?

[bob p]

I think attenuators came about as a result of the Led Zeppelin era. Jimi. Whatever. In those days three 100 watt MArshalls stacked each on two 4x12s was your basic stage rig. Hell, even our band had to compete with a guitar through a 100 watt and two 412s. "Hey, turn that down" everywhere we went. SO everyone wants that cranked to the sky sound, so the attenuator is born.

I remember things differently, but then I'm thinking about a different context. Prior to the Jimmy/Jimi era I remember working musicians (wedding, lounge, venue working stiffs) owning a collection of different sized Fender amps, and choosing which one they took to a gig depending on the size of the venue they were playing. Even in the old days preceding the 70s rock era there were guitarists who liked to crank their amps into the sweet spot for tone, albeit in a more subtle way than we see today. Back then it was more of a compression / cusp of distortion thing that people were looking for. Before attenuators were available the standard solution to this problem was to own a Deluxe Reverb, a Vibrolux Reverb and a Twin Reverb and to choose the right amp for the occasion. For the most part these guys were working stiffs, not necessarily rockers, who just needed several tools available to match the gig they were playing. Attenuators would have vastly simplified logistics for them, but back then attenuators just weren't available.

But I agree with you in the context of the Jimmy / Jimi era and the effect that they had on changing the tone that guitar players sought as their target. Still, when I think of attenuators, I'm thinking about how they were deployed in terms of exactly what it is/was that people using them are/were trying to accomplish.

Jimmy and Jimi are famous for the 100W stacks running balls out, but their attenuator was a large room and their iconic sounds were a combination of amplifier distortion and speaker distortion. They didn't produce their signature tones, which so many people tried to emulate, by using attenuators. They just dimed the controls and rocked out. Their fans, who didn't have large venues where they could run their amps balls-out, eventually started using attenuators out of necessity when attentuators became available as they tried to capture that large venue/cranked Marshall tone in smaller venues, venues even as small as a bedroom today, where high obtaining tone via high SPL was prohibitive. But that deployment of attenuators came along much later. I think it's safe to say that in the era that Jimmy and Jimi were performing live and creating their iconic sounds, not one average Joe at home was running his amp into a loadbox.

Recording changed forever when an MIT engineer named Tom Scholz wanted to get that cranked Marshall tone for recording the Boston albums in his basement studio. He very specifically wanted to separate amplifier distortion, which he found desirable, from speaker distortion, which he found undesirable, using amplifier-only distortion in his recording paradigm. He designed his own attenuators, which are likely to be the first time on record that attenuators alone were purposefully used to create cranked Marshall tone without speaker distortion. I know you're old enough to remember when the first Boston album came out in 1976. At the time it brought a radically new sound to the radio. I guess it's hard to remember how groundbreaking that album was, looking back on it 40+ years later.

Why does this matter? Unlike Jimmy and Jimi who didn't use attenuators during their rise to fame in the late 60s to early 70s, by the mid 70s Scholz had designed an attenuator for the purpose of creating recorded cranked tone. I think that was a first. Now everyone is doing it, both in the studio and at home. And a lot of tube have died because of it's popularity.

[Enzo]

I don't think we disagree much, pre Jimi, those guys with the Fender collection were never going for power tube overdrive. It was the advent of the Jimi type LOUD rock band that got us all into the wall of amps deafening sound. So when later guys hear old Zep records, "Hey I can do that" but they need it to be not deafening.

Yes, the big stars playing arena rock could plays balls out. But the local club warriors couldn;t get away with that.

Old? I remember when the first Jimi album came out, I was on the radio. The music director came in and asked me to check out this new thing, "it's sorta psychedelic Motown or something". 1967 maybe?

On amps in the old days. Ther was a local dance bar, The Coral Gables, where the bands all played. We played there, with our Jimi Hendrix guitarist. One day a new band was booked, and I suspect the agent oversold them to the bar. The "band" pulls in, the drummer has a kick, a snare, and one cymbal, the other two guys played guitar, and the both plugged into one Deluxe Reverb. That's it. They lasted two days and were shown the door. Not their fault, they were who they were. But it was an interesting contrast to bands playing Jimi and Zep. But they were not loud, honest.

[Chuck H]

Today adjustable bias and attenuation are ubiquitous. We're seeing lots of hot-rodded high-gain amps that are being run with HOT BIAS into RESISTIVE LOADS. That's a deadly combination for tubes. And everyone is doing it. Maybe the reason that EL34 are getting such a bad rap today is that people just aren't being very kind to them, and because being pentodes they're just not as robust as beams.

For the record... It's been my experience that el84's (a pentode if ever there was) work just fine in this scenario. I've been beating the crap out of el84's with a hot bias at 355 to 365 plate volts run dimed, and pushed to the edge of over dissipating the screens in my designs for almost a decade!!! 470R screen resistors rather than the prescribed 1k! And I AM using an 8k primary for a pair and a 2.2k resistor rather than a choke, in case you wondered how the impedance played out for screen dissipation when clipping. I get well over a year from a pair of tubes with typical hours CONSTANTLY DIMED INTO AN ATTENUATOR!!! The el84 is a tiny little skinny tube that has every reason to be microphonic and tender as a true pentode, yet... It also has the property of gain and VERY low bias relationship that means closer and more strict tolerances. I think it's only because this is a popular tube that we can still get good examples. How did the el34 lose popularity??? I would have thought that SOMEONE would be offering a good example of this tube. They would certainly own the market. How much of a market that is might be the issue. The Shuguang is a great tube with the exception that (every one that I've bought) it tends to microphony. Not so much that it's a problem in head style cabinets, but a deal breaker in combo's. Leave it to the Chinese to find the unexploited market. They do it all the damn time (god bless). If you need an el34 for a Marshall head I really think the Ruby el34B is the ONLY option anymore. YMMV.

[soundmasterg]

When I see high B+ and high dissipation, I automatically think "fan". Lots of high power amps use them, it helps. It's also a cheap upgrade. The problem is that budget amp manufacturers won't even consider adding a fan due to cost.

I have one of those old Silvertones. They don't have a high B+ and they're not biased hot.

Those Sovtek MIG 60's were particularly brutal on the power tubes, and they come stock with the Sovtek EL34G, which is about as lousy an EL34 type as you might find. I thought they had all self-destructed by now! Fans do certainly help but no one will add them due to cost or lack of knowledge.

Those Silvertone 1484's are about 440V-450V, non-adjustable bias, and an output transformer that is smaller than what is in a Champ. They're only 25 watts RMS and have a ratty sound that has become popular. But they also use 6L6GC's which as a beam tetrode are much more reliable than any true pentode like an EL34 would be. That said, most El34's are MUCH MUCH better than the Sovtek EL34G was/is.

Greg

[Sowhat]

Heck of a thread here, lot's of opinions, most of them pretty reasonable but some things I disagree with but then again I've only got some dubious evidence to back me up like everyone else does. I suppose if your not actually working in the tube factory yourself you can't really know the absolute limits of these tubes. I build some dual master Mashall clones like the JCM800 2203 and 2204 from time to time and I put in the beefy Mercury Magnetics transformers which supply 525 volt B+. I just order a matched pair or quad of JJ EL34's from AES and slap them in. My customers can't believe how good my amps sound and in the 5 years I've been making these things, I've had no complaints or failures... I think it's the transformers that make the difference personally.

[Chuck H]

I think it's the transformers that make the difference personally.

IMO, sort of. Lemme splain.

If you're making classic designs then you are using output transformers that have a lowish primary impedance and, since you're using good iron (no one said Mercury wasn't good, just that it's overpriced to cover their marketing) the choke is likely a key performer here also. IME it's high frequency spikes during overdrive that over dissipate the tender screens of modern el34's. A lowish plate impedance and a choke who's coil has sufficiently high impedance at high frequency helps prevent high frequency spikes from finding a path through the screens rather than the plates. The amp I was popping el34's in uses a 6.6k primary and a 470r resistor between the plate and screen supply. Chances are that the OT HF impedance is sufficient that spikes during clipping were finding their way through the screens rather than the plates. This, combined with the newer tubes tender screens was almost certainly my trouble. Increasing screen circuit impedance and lowering plate circuit impedance is the solution. Lesson learned. In your case I would bet it's the design, rather than any sort of brand/quality for the iron that is working in your favor since it has the aforementioned properties.

[Mick Bailey]

You'd suppose that with the relatively high failure rates of modern EL34s that new Marshall amps would be dying all over the place, but they aren't. When I've bought OEM 'Marshall' tubes (actually Shuguang) they last just fine, other than in amps with super-high plate/screen voltages such as some Traynors. I think the microphonics with Shuguang is largely down to the super-thin envelope. I don't see this to the same degree with the TAD branded Shuguang tubes with the thicker glass. I used to think that the mica supports may have been the problem, but experience with the 6L6EH (that use spring wires on the supports) to compared to the Sovtek 5881 (that doesn't and are no more microphonic) leads me to think a plain mica support squeezed into the envelope is OK and the problem lies elsewhere.

Is there any company that claims reliability as an attribute?