JJ E34L failure(s)

[cogsncogs]

Hello everyone

As of the summer of 2003 I've had three (two blue glass, one clear) JJ E34L's fail exactly in the same way; The internal connection from the cathode sleeve to the cathode pin became "unwelded" at the cathode sleeve.
There seems to be a very "serious" QC problem! I run my E34L's with a standing current of 35mA @ 440V anode, ULT PP. No cherry plates ever, those babies should never exhibit that type of failure! I understand thermal stress of cycling, turning the amp on/off, but I know I haven't exceeded what's considered "normal" cycling. Has anyone else had this happen?
Looks like it's time to get out the plastic and get me some EH-EL34's, or some "winged C" Svetlana's. Any suggestions?
Shame though, as the I really liked the sound/look of those critters! I choose the JJ's because they were reportedly/advertised to be able to withstand 600V on their plates! I was planning to mod my amp to apply close to 500V on the plates and get a little more "balls" out of it!
I also had another blue glass E34L fail. After setting the bias to 35mA, the bias current after 15-20 minutes would slowly start to climb waaayy past normal. 35 -> 50mA before settling down. Probably a gassy tube, or misaligned grid wires (sagging?).
I think maybe if I were to purchase the JJ's from a better dealer who tests and weeds out the marginal performing stock, I could do well.

Any comments would be welcome!

Happy New Year!

Wayne

 

[SY]

That's just wrong. This is the sort of stuff that any self-respecting manufacturer would not let out the door. I've been using winged C's, not happy with the consistency unit-to-unit, but none of them have died on me.

 

[cogsncogs]

I might also add, out of 2 sets of matched quads I have two left! So now I'm using a matched JJ on the left (closest to my sitting position in front of the computer) and an unknown brand, Chinese or Russian (look like sovteks from the mica spacers) matched pair on the right. Just burns me up! And UPS is running behind schedeual due to the weather, airline companies computer crash (?). Dratt, I don't want to dig out my SS monster fro New Year's!
Could take a road trip to Dayton Ohio, about 4 plus hours!

Wayne

 

[DigitalJunkie]

I've had good luck with the EH EL34's in my ST-70.
Not so great luck with the Sovtek 5AR4,Had a couple start arcing at the bottom insulator,from the cathode to plate,in the same spot. (it's a pretty small gap down there.) Been using a 5U4GB since the last one arced over.
I'm sure it's not the filter caps,I checked the leakage of the stock can (still performs quite well!) but replaced it with the SDS labs cap board just to be sure...Still arcs.

 

[nanana]

hey digital junkie,
what is the input filter caps value? is it above 47uF? many people "mod" the power supply by adding capacitance or new caps (which are really better than old ones) only to make it a rectifier killer. if you have any doubt about what i am saying, please read (or reread the chapter on power supplies in any RCA tube manual... a good little reminder if only that) if so... almost any rectifier you put in there will have a rough time because the inrush current is exceeding the peak current of the rectifier (that is why it arcs, not because it is a piece of ****). try putting a 50 or 100 ohm 5W resistor in between the cathode (pin 8) and the first cap...
happy new year!
jc

 

[cogsncogs]

Hi Everyone

I'm looking to order a quad in the next 2 hours in order to guarantee delievery by Friday, New Years Eve. So I'm in a little, tiny hurry hehe... Has anyone had any experience with the Electro-Harmonix Fat Bulb 6CA7? What I'm looking for besides good CRAFTMANSHIP (remember those days?) is the ability to handle a good high plate voltage, 800V would be beautiful, but will settle for 600V. If I could get my PS up to 475V, which I can very easy (taps on my PT) except for locating good 220µf - 470µf 350WV snap-in caps, I'd be in tube heaven! Can't seem to find the caps I need that will fit without to much fuss, 30mm max in diameter without having to resort to using clamps.
And BTW that trip to Dayton would be 9-10 hours round-trip! When I was a kid you could go to almost every drug store on the corner and buy tubes!

So I've narrowed it down to 4:
EH Fat Bulb 6CA7
EH EL34
S.E.D. EL34
Sovtek EL34WXT

Thanks
Wayne

 

[nanana]

i hate to be a party pooper or rain on anyone's parade but the problem is not the plate volts... almost any EL-34 can take 800 or 900 volts on the plate... (that was the way they were run in class C) providing there's only 250 volts on the SCREEN! you CAN"T PUT JUST ANY OLD B+ ON THE SCREEN AND EXPECT TUBES TO SURVIVE. all those UL amps with 590 mains are tube killers. it makes me crazy to see just how nutty people are when it comes to remembering the most basic stuff about tetrodes and pentodes. please look at the tube manual. 6CA7 is even less suited to high volts on the screen although everyone does it. it doesn't even have a shadow grid... so it lights up like a christmas tree once the screen supply goes anything above 400. thats actually OK for awhile... it was made that way, but above 450, it starts to get to the temperature where it begins to stretch... no matter how skilled or careful the tensioning is, there is a limit to the geometry. the welds don't melt but the wire tends to break just above the weld. BOOM! they do sound nice before that happens though... the 6CA7 is a tetrode, not a pentode (sarnoff wouldn't pay philips the license money) so its performance is different from the EL-34. both are nice, just different.
ranting ranting
jc

 

[Geek]

Could there be paek cathode currents causing it to open up like a fuse?

 

[richwalters]

That's just wrong. This is the sort of stuff that any self-respecting manufacturer would not let out the door. I've been using winged C's, not happy with the consistency unit-to-unit, but none of them have died on me.

Umm.....not sure about that one....EI let me down with a batch of EI KT90's used in UL mode, which when tapped were short- circuiting internally from G2 to G3.... Luckily I had a fuse in the O/P tranny primary.....So far no problems with clear tube JJ88's nor Svet 6550B. Due to the expense of the o/p tranny I can recommend putting a fuse in the centre tap lead. The sonic difference is nil.

When one orders tubes, insist the "thump test" be done before they leave the door.

rich

 

[cogsncogs]

being scolded???

Hi jc and everyone

I lost you guys for hours yesterday, Site not found! So I'm a little late in posting a response. Am I being scolded jc?

I know all about the diffs betwixed an EL34 and 6CA7. 6CA7 is really a beam tetrode with beam forming plates, like a KT88, KT66, 6L6, and one of my faves the 7591. No one (me) here is talking about an amp with 800V anode voltage. Class B would be design max 800V anode, 400V screen of a 6CA7 tetrode, Push-Pull "Pentode Mode", 100W for a pair! (published rating hehe!) A friend of my Father built one around 1960 or so. Don't remember how well it worked tho! It was probably always on the verge of melting down! Of course you could tweak down the screen voltage to keep the tube from self-destructing! Then you might as well go for Horizontal Output tubes. Much higher plate dissipation.

What I'm asking about is quality/headroom! I've run 6CA7/EL34's with 475V Class AB1 Ultralinear PP for years back in the 1960's and 70's. Westinghouse, Mullard, Sylvania etc. They lasted for years with no problem at all! I tried a set of Rat Shack EL34's, continental slimmies as they were known back then, cherry at 430V with cathode or aka self bias. Got in a big argument with the salesman! Lifetime guarantee plus gold plated pins ya know! Got tired of it (and him) and put in a set of Westinghouse EL34's, no problem! Same operating point, using a 5V3A rectifier. Did try to use the Rat Shack ones at a later date, with fixed bias @475V. Had to bias them way down near cut-off to keep them from self destructing. I threw them away! Wish I kept them tho for posterity!

My JJ's didn't fry! They were actually operated well within spec! About 15 watts plate dissipation. The first JJ to exhibit the broken connection at the cathode sleeve was about TWO days after I installed it! Operated with 440V plate voltage @35mA cathode current, fixed bias, class AB1 ultralinear PP 5.5k OPT. Tapping the tube caused it to make/break the connection! Same thing happened to the other two except a year or so later, this past week for one and two months ago for the other. There was no so-called melting! I hate to pee on this "parade" but I'm no toobe-noobe!

I was thinking of running them close to a very well known operating point. For example:
Data taken from Amperex data sheet.

Two Tubes Push-Pull Class AB1 Ultralinear Connection

Vbb: 500V
Grid #2: taken from tap @ 43% of plate winding
Grid #1: -44.5V
a-a: 7k
Plate plus screen current (no signal): 2x57mA
Plate plus Screen current (Max Signal): 2x112mA
Input Signal (RMS): 32V
Power Output: 60W
THD: 2.5%

That's the about the max you can go with an EL34 UL PP! About 24.5W plate dissipation. I do know for a fact there were/are tubes being made that you could not do this with! I want to operate them close to 475V (not even 500V!) at around 33mA of standing current, @16.7 watts plate dissipation to get a little extra power. May need to increase the screen grid stoppers from 100R to 470R - 1k. IIRC David Manley (opened a can of worms around here!) of VTL did so in his amplifiers (500V Vbb) as did many others. So jc, I don't get it?
Believe me I understand what you are saying. I have no intention of going anywhere near (gulp) 800V! They don't make them like that anymore. Even then it was pushing it! And yes there were EL34's made that could not go anywhere near 800V no matter what screen voltage was applied. My experience with the 6CA7 is very limited and from long ago! My thought of possibly using an EH 6CA7 fat bottle is merely out of curiosity and nostalgia!

There is a certain make of an EL84 that can only handle 250V anode (Svetlana?), as apposed to 300V or can be pushed a little higher, i.e. certain makes of a 6BQ5/EL84, watching your cathode current and screen voltage/current of course. You can do this by using the ultralinear mode of operation. And lets not forget the size of the grid leak resistor, for stablity.

That 800V was a wish! More volts, more power. I wouldn't even consider doing so! Anyway class B is not my cup of tea! It's just that there are some EL34's that can handle a higher plate voltage along with the high-ish screen voltage "supposedly" better than others. Better built in other-words. Did I even say I wanted to "stick" 600V to my toobes anodes? Bad day jc?

Cheers jc
Wayne

 

[SY]

Wayne, what you described is clearly a defect in the spot-welding process. It does happen (I've got a DOA 6528 with that problem, waaaaaah!), but it's preventable and ought to have been caught during production.

 

[cogsncogs]

Hi Geek

Could there be paek cathode currents causing it to open up like a fuse?

Nope! No-waaayyy dude! Just bad welds! In one of the JJ's the cathode sleeve was barely sticking out of the button mica. In all three failures "tapping" the tube made or broke the connection. I actually had one of unknown manufacture (brand new out of the box!) were the cathode actually came loose up through the top of the tube!

Reading the "reviews" and comments of the different brands of the EL34 on certain sites were conflicting and confusing, well not really! I guess everyone is entitled to their own opinions misleading or not, especially the manufacturers! I think I'll settle on either the Electro-Harmonix or a "Winged C" Svetlana.

Thanks for your input guys. And you too jc! Not a personal attack, OK
I consider diyAudio my home and you guys as fellow audio/diy fanatics! I want to keep it that way!

Cheers everyone
Wayne
A fellow vacuum toobe freak!

 

[cogsncogs]

Thanks SY!

Wayne

 

[Geek]

Man, that sucks!

There's some bad runs out there. One of the EU brands (can't remember the brand, EI, EH, JJ?) discussed on rec.audio.tubes also had a bad lot - KT-90's with "hotspots" on the plate due to the grids not evenly spaced

 

[cogsncogs]

@ Geek

As concerning "peak" cathode current, my little 6U8 split load phase splitter would "clip" way before that would happen! Well that's not taking into account the higher third order distortion products produced and the NFB trying to compensate! But I've never driven my amp into that sort of clipping, at least I don't think so... except maybe when you're tipping back on Grandpa's cough meds! hehe! Or Uncle Jack's!

Now when I get my new front-end built, a 6SL7 -> 6SN7 LTP or a 9 pin version, that may happen! Maybe a 12AV7 -> 6GU7 LTP. Haven't really decided yet.

Cheers Everone!
Wayne

 

[nanana]

hey cogs,
no i wasn't scolding you... just venting. 475volts on the plate of any of the tubes you describe is not the problem... it is the screen. UL operation puts the plate supply on the screen obviously. you can get away with pushing things a little bit more in UL because the screen voltage tracks the plate swing, reducing the current when it normally (pentode mode) would be highest, and that is when the plate voltage swings below the screen voltage. the defense, that nearly ALL manufacturers and DIYers alike run to when they have a problem - and please understand that i am not defending EI or JJ or Russia Or GE RCA or anyone who made/makes tubes... i AM complaining about the end users specifically- is, and its a classic, "but my 1937 tungsylvmulloram EL749's don't blow when i abuse the **** out of them?" think of jimmy hendrix's experience at the fillmore east (in NYC) for his return show with his new Marshall amps (all three blew up and no jimmy wasn't the only one with that problem)
the max rated screen voltage of an EL-34 is 400 volts. the plate dissipation is 25W but what about the screen dissipation? how many watts can it handle? 4.5 watts continuous (10 watts with a 50% duty cycle, which it would have in class A, class B is much harder on the screen with the long periods of plate cut-off). how much current does the screen draw at maximum signal in class AB1/2 with 400 volts? 25-35 mA (10 to 14 watts). the max screen voltage of a tungsol 6550 is 350. the 6L6GC is 450. EL-509 is 300. but more important is the current drawn at those voltages and the heating that takes place that makes the worst kind of non-linear distortion you can find in a tube. the tube is not happy being run that way in the first place! its not called maximum for no reason! and don't tell me that the current limiting resistors will fix it... what is the effect of putting a 5K resistance in series with the screen and then swinging the plate volts below it? its called feedback! and it only kicks in half the time... the effect of high screen voltages on perfomance is a long discussion for another thread... but it isn't only the screen that gets beat the hell out of by the end user without any thought! the maximum heater to cathode voltage on all commercial tubes except for the 6AS7 is 100 volts positive (6922 is 60), you can go more negative without problem. anyone who knows about the chemistry of the cathode will appreciate the importance of this and yet how many manufacturers and diyers regularly implement cathode followers these days with grounded heaters? almost ALL of them. "my smoothplate $3$%@97867s never blew up..." oh yes they did... anyone that worked at tektronix or HP in the 60's, or just fixed tube stuff for a living can tell you a little about that. 500 volt UL operation with any of the tubes you describe is going to beat the hell out of the tubes of ANY manufacturer from ANY time in the period that can be descibed as the tube era. and before you yell at me, please take a moment to peruse your tube manuals... the part that describes the voltage gradient that exists in a tube between cathode and plate... the part in "how a tube works" just to refresh your memory. and if you do think you know how a tube works, you should take this opportunity to calm down and think things through a little. what happens when the nickel wire the screen is made of is heated to or above 1100 degrees kelvin while sitting at a positive voltage gradient between a cathode and plate? what happens when it is connected back to the supply through the output transformer?

and what about fixed bias operation of a power tetrode (RC coupled) with a large grid resistor (like 220K)... when the manual clearly states that the maximum is 50K? the manufacturer knows that all the bozos are going to ignore this but they have to cover their butts... "my tubes keep running away and melting, they must be ****!" i could go on and on... but i think i've over done it quite a bit here!

also, the peak current comments weren't about the JJEL34s, that was concerning the rectifier... if you see a rectifier arc over during turn on, that tells you right away that the inrush current is higher than the cathode can provide. as the cathode heats, it goes from nada to some very finite amount of current... if the caps pull it away faster than it can be emitted, arcing can and does occur... (there are no grids in a diode!) its a crude but reliable way of knowing if you have selected the right amount for the input filter cap... you can not just put 220 uF after a tube rectifier... not without consequences. "but what about my 1963 genorama GZ652s? theey never blew up when i did that!"
jc

 

[richwalters]

Hi there.......with NOS tubes one can run to yester-years B+ values....but who would ?...I can run the orig 6550A GE for a sim o/p as a KT88..in a 500V B+ fixed bias amp....they were known as <good tubes> and the KT88 GEC spec sheet does give the 6550A as a near equiv. The more recent 6550C is really fit for amps with cathode bias operation.

Unfortunately nearly all manufacturers don't really tailor the fleece from the cloth.....exhausting tubes costs time and money. The history of the 6550 was compromised (costwise)for mass consumer audio production of it's time...look at the recommended bias resistor values when compared to KT88's or EL34's....these indicate how deep the vacuum is.....my test is sustained current throughput at full power til anodes glow cherry red and suddenly return to no sig quiescent, that is Does the quiescent value sit exactly as the set value ?

It's a fact of life that we all have to derate modern-made tubes, run them cooler and with lower B+ or use parallel pairs to get a sim o/p power for reasonable working life.

I've had a nackered life and now retired.

With the screen current.....Nowadays I always put a resistor in series. Remember, using fixed bias the operational working voltage of the tube is higher as the bias is neg w.r.t ground. an amp using 550V B+ with -60V bias; the tube is really seeing 610V B+ within it's innards.

rich

 

[nanana]

with all due respect, and with particular mention of what has probably been years of experience with tubes and their uses by many members of this group... i would point to the previous email as exactly the problem. and i am not picking rich out, because his point of view is probably the norm.

let me ask one question before all hell breaks out, if it even does (?)...
why does one want to put 550 volts on a particular tube?

what is the goal? what aspect of the performance is the key to understanding this decision? one would have to track back through a host of decisions to get to the core but i will guess that when it comes to a 6550/KT-88 (same tube) that it is output power that guided that particular decision... and along with it some kind of understanding or belief that more or most is somehow important. so, other aspects of the design of a tube output stage might take a back seat in the bus in order to focus more clearly on power. and so we would arrive at 550 volts somehow (its less than the 600 volts max plate volt rating and yet only 200 volts over the max screen rating... or something like that).

now lets just say for a moment that some other quality became the focus. like harmonic distortion, for example. well, if we were stuck with a 6550, and couldn't get anything else for the moment, we might look at things like spectrum analysis of different operating points (as opposed to just spice modeling it) and we would most likely find a very different series of decisions about the power supply... most likely we would find the screen voltage would be held to a value near where the plate swing would not dip much below in order to reduce THD (in tetrode), in triode mode with reduced plate voltage, or some clever feedback arrangement (such as UL) to reduce the 3rd and other odd harmonics favored in power tetrodes. the power supply would definitely not allow the screen supply to get anywhere near the plate or the plate maximum as it would make any of the previously mentioned efforts unlikely or without improvement.

there are other things we could focus on, like max working life or lowest damping factor... etc. only one point of view i can think of at the moment would gain advantage from an elevated power supply... output power.

the way tubes are operated today are far in excess of the way they were before... when was the last time you looked at audio research, CJ or some of the smaller companies products? i see them and talk to the manufacturers all the time. all of the currently produced 6550/kt88 tubes made today exceed the original specs for plate dissipation, screen dissipation and peak current... all of them. the guitar amp business destroyed most of the surplus tubes that most of you all wish you could find... that is a fact. ask marshall how many mullard EL-34's they bought in the 70's right up to the closure of philip's tube production. they won't tell you. fender and 6V6s. you won't hear a word. there are many other problems with tube manufacture in the "developing world"and there is no question that there are QC problems. but those problems are only half the story. for awhile, the yugo 6550s were all that was available and yet companies like ampeg could regularly get 5+ reliable years out of a sextet of unmatched 6550s (300 watts in the SVT). not one hifi manufacturer could claim this through the 70s -90s. thats because the engineers at ampeg were a bunch of really old guys and know tubes like old guys do.

the nice thing about all this is that anyone can just go do whatever the hell they want to with tubes! and then they can say whatever they think too... i am one of those also! i think that the end user has focused on particular goals to the benefit and detriment of the business. thats all... i think its good for someone to point this out from time to time, too.
jc

 

[cogsncogs]

I believe the maximum rated screen voltage is 425V Design Center. 450V max for a JJ E34L not a JJ EL34. Svetlana claims 500V, but I'll take that with a grain of salt! Max screen dissipation = 8W, that would be peak power at some unknown duty cycle I would guess as opposed to static or continuous power. As with any tube it's best to always operate them on the conservative side.

I have seen the screen grids on an EL34 glow red hot. Cheap ones mostly! Rat Shack Gold Pin with Lifetime warranty. Now I'm not talking 6CA7 now. I'm trying to figure if you are saying 440V on my poor screens is way too much in my ultralinear amp. That would mean everyone has been wrong since the EL34 came out, including Mullard! It would be very easy to melt your screens in you guitar amp in that config! But I'm not Jimi Hendrix! And this a Hi-Fi amplifier I'm talking about, where I don't drive it into almost continuous overload! Those screen grid resistors also limit dynamic power reflected back into the screen grids!

As I have said, I have used a 475V supply, fixed bias for an EL34 ultralinear PP Hi-Fi amplifier for over 13 years, 1971 to 1984 without one single output tube failure or any sign of red-hot screen grids. And besides I don't want run my tubes at 500V, though it is possible but your are most definitely pushing it and your luck!

At the moment I'm using 270k grid leaks in EL34 amp 40W, 440V. David Manley of VTL used 390k, crazy!
At 475V I wouldn't go higher than 100k. Using cathode bias you could go higher but... Yeah I've seen 6550's and KT88's with much higher than the maximum 50k. tsk tsk.

I do know a little about tubes. I know you probably don't care and I doubt if anyone else here at diyAudio cares either, but I worked as TV, Radio, Hi-Fi, PA amps, anything with tubes and SS Repair/Bench Technician for many years. My baby bottle was a tube. It was always fun watching a 40KN6 meltdown from the absence of drive (horizontal osc. failure)! I used to read the RCA 1959 tube manual as a bedtime book! I do happen to know that the screen grid has more influence on plate current than the plate does! That's the whole idea! The suppressor grid is there to "repel" the secondary electrons (secondary emission) "knocked" off the plate by the stream of electrons striking the plate, back to the plate.

In my original post(s) I was looking for a current production EL34 the meets or EXCEEDS the published ratings! The JJE34L was/is one such tube except for the faulty/bad welds. So please forgive me, but I just don't see how your ranting is "helping" me any. My god man, read my posts, ok? It looks like you are assuming I want to build an amp that's way out of the reach of any EL34!

Since I have a multi-tapped PWR transformer, if I run into problems at 475V, I can always switch to a different tap and step it down a little!

Wayne

BTW I don't particularly like Texas. I hope I never see that place!

 

[nanana]

hey cogs! i definitely wasn't picking on you! please please understand i am just ranting at the tube world in general... you just happened to put your finger on a sore point. i apologize right away if it came off as picking on you. not at all my intention! nor rich walters either. sometimes a train of thought takes one off south of the border and before one knows it, beyond texas! i have been around the business too for some time and feel warm and protective of it and the hobby too! its good to be in such company, believe me!
jc

the apologetic ranter