Current Production Modulator tubes EL34 Etc.

[KB3DKS]

 Reprinted from the Tube Collectors Group.
Author is the well respected Eric Barbour.

"All the current factories have certain consistent, "proprietary" inadequacies.
Most of the issues are due to guitar amp manufacturers demanding the lowest possible unit cost, forcing the factories to hire workers at below-market wages, and then pushing the tubes thru the production line as fast as possible.

Result: none of them are pumped as long as they should be. That is a major issue with ALL of them today. The cathode formulas are also not as good as the olden days, so lifetime will be shorter. Chinese mass-market products usually have awful cathodes, no matter how much more you pay for a "premium tube". Maximum cathode emission is also weirdly consistent for each factory. Chinese were always terrible,New Sensor tubes from Reflektor were erratic, SEDs were passable, and JJs had great emission profiles. (Back in the 1990s anyway.)

But vacuum hardness is the worst problem. It becomes especially bad in power pentodes in which the screen grid runs very hot, like EL34s. Nothing outgasses and ionizes that gas as beautifully as a white-hot screen grid. And nothing makes a screen grid hot like operation in a guitar amp, in which the screen is hooked directly to the main plate supply, insuring the screen will be drawing more current than the plate for at least part of the AC cycle.....why? Because "that's the way they did it in the 1960s". Guitar players are all about doing everything just like the 1960s.

In researching for VTV articles, I learned little tidbits that you can't find easily any other way. For example: did you know that GEC-Genalex KT66s,KT77s and KT88s were very "costly" compared to other brands in the 1960s? Major reason: they pumped them for ONE HOUR, not one half-hour
like most American factories. And if a customer wanted maximum quality, for a military contract, they left the tubes on the pumping stations overnight. Supposedly all of the TT series transmitting tubes were made like that.

Every Genalex tube I ever tested had a marvelous rock-hard vacuum, even tired old KT88s that had brown oxide-gunk all over the inside of the bottle.

I had this charming routine with the Svetlana/SED factory people. They had to deliver 10,000 EL34s to Marshall in the UK every month on a contracted schedule. They only had four 24-station
pumping machines set up for EL34s, just barely enough to process 500 tubes per day shift.
So (very) roughly once a year, I would get a nasty little note from some bloke at Marshall, blubbering that "the last batch of EL34s is blowing up!!" And I would have to send Vetrov's
office a fax (when the Russian phone system was working, which was random, no they didn't have working email) telling him to please pump the tubes for an extra 10 minutes.
He would deny any changes in the production procedure, but the next batch delivered to Marshall would work okay.

Presumably, since those early days, they've figured out that it's a good thing to keep their biggest reliable customer happy. 120,000 tubes a year is not trivial today.

If you're looking for a "good" current EL34, Marshall is the largest user in the world, and they still choose SED over anything else, despite having to pay about $1 more for them. (The horror!! A whole dollar more!!!)

JJs are also pretty good, although they are prone to the same occasional pumping "shortcutting". You are welcome to mess with Sovtek/New Sensor and various Chinese makes, but don't
blame me if they arc over and kill your output transformer. Don't expect sympathy from the dealer.

New Sensor is always "fun" to have a discussion about tube quality with. Mike likes to scream obscenities at people. Good ol' Mike.

This is why, if you want to build a tester that really exercises a power tube with a screen grid, just set it up so you can run the screen very hot. I mean white hot, not a little bit red.
A really good new-old-stock EL34 can handle 40-50 mA dc on the screen with a 450v supply. No, I'm not kidding.None of the current ones can do that. 15-25 mA is usually the limit before the gas ionizes. Or something else fails.

Serious advice: put a fast-blow fuse in the plate circuit, rated at roughly twice the maximum plate current at full power. 400 or 500 mA is a good figure for two EL34s."

E. A. Barbour
METASONIX
www.metasonix.com

[WD5JKO]

Reprinted from the Tube Collectors Group.
Author is the well respected Eric Barbour.

http://www.youtube.com/watch?v=by7nNwQe_Sc

 

Jim
WD5JKO

[k4kyv]

I can't believe tubes are such a hot item these days that the factories are having a hard time keeping up with production demand, to the point that there aren't enough hours in a day or a week to properly evacuate the tubes during the manufacturing process.  30 minutes pumping time as opposed to an hour?  Gimme a freakin break! They should have ample time on their hands for 24 hours of pumping time per tube if that would result in a better product.

I wonder if the offshore manufacturers, now that they have a captive market, are intentionally reducing pumping time to keep tube life short in order to sell replacements to the customer more often, hoping to pull in more big bucks from the guitar amp and audiophool markets.

Maybe that explains the notorious reputation Chinese and other foreign-made transmitting tubes have long had for premature crap-out. I could understand earlier production runs being of inferior quality, since most of those manufacturers were new at building tubes, but the tube-makers have now had ample time to fine-tune the process, work out the bugs and get the hang of quality control, so they should be  capable of making a product every bit as good as the best ones made by RCA, GE and Eimac in their heyday.  Towards the end, US manufacturers started cutting corners in tube production too, resulting in an inferior product.  Case in point: 807's originally used ceramic insulators as part of the support structure, and had a little shield at the bottom of the plate/grid structure where the wire leads go down to the base.  The most recent USA productions used nothing more than mica sheets in the support structure, and omitted the little shield, resulting in tubes that are less rugged and even more squirrelly than the original 807... basically a glass 6L6 with the plate lead coming out of the top and a tan 5-pin base, otherwise not too different from a sweep tube.

Sure, they probably pay their workers 50¢ a day, but the US manufacturers didn't do all that better and they still managed to get highly skilled workers.  In the mid-70s I periodically serviced a piece of equipment used at the GTE Sylvania plant in Salem, MA, where they made light bulbs. That process required pretty much the same skills needed for assembling vacuum tubes, in fact, they may have once manufactured tubes.  Most production workers were women barely paid more than minimum wage. It was tedious work that required high manual skill and dexterity, but nothing that required much formal education beyond OJT for the specific task.

[N4LTA]

Not that I am not believing all this - but Mr Barbour worked for Svetlana USA and they folded - more or less could not compete with New Sensor.

I happen to buy about 300-400 New Sensor 6V6s a year and use them in my products. You know how many got returned last year? ZERO. I have found them to be reliable tubes when used to the old USA specs. I use probably 200 5Y3s a year Sovtek and I had two bad ones last year. I had no JJ 12AX7s returned last year out of 250 or so sold in my amps.

Botom line - don't believe everything that you hear.

120,000 EL34s a year for Marshall sounds like an awful lot.

That would fill up 30,000 to 50,000 amps. Thats a lot of $2000 - $3000 guitar amps.  Maybe so - I have no idea.

[KD6VXI]

i'd be willing to bet that Marshall is MORE in the tube reselling business (and rebranding) with the volume of 120,000 units a year.

Could be wrong, but maybe they have a couple E-Bay accounts for dumping them to the phools?

--Shane
KD6VXI

[KB3DKS]

Well,
My reason for posting that info by Eric B was to point out that most current overseas production cannot equal the quality and capability of NOS USA or older Euro made audio power tubes mainly due to inferior production practices whatever the reason.
 For Amateur use it is best to ask around the radio community which has a good stock of tubes tucked away, and look around Hamfests, etc for real US made tubes.
  I know from personal experience that the screen grids of most all current Overseas made EL34s have serious issues regarding peak voltage and current. The winged "C" Russians seem to be the best out of them all but quality varies. I know of none that can be strapped triode screen to plate and operated at modulation voltages.
 Personally I use Sylvania or RCA 6CA7s which have a screen rating of 450v with 450v plate or 425v screen with 800v plate and can certainly exceed that in amateur use. The main shortcoming is the bottom plate connection. With a good ceramic socket a must.
Also none of the tubes have anywhere close to the amount of cathode coating that used to be used and have a much shorter useful life accordingly.
  High power Russian Surplus transmitting tubes are a different story as these were made to a Mil spec not audiofool requirements.
Bill

[W2VW]

There's a whole lot of very questionable tube information on the WWW.

Audiophools and users of the diathermy band have added to the black magic.

[KM1H]

Erics response was part of several discussions started by my asking about 6550's.

Well, Svetlana USA did get their nuts in a wringer due to a scam pulled by the owner of New Sensor so Id be a bit peeved also. Eric was in marketing while I did a lot of RF testing as a consultant to George Badger, W6TC, a bit before Eric arrived. In the end marketing won and overated milsurplus hit the market with fancy Eimac type designations with delusional dissipation ratings. The current (relabled GU-74B) 4CX800A panic is one result. I have a copy of the original Russian engineering test data on the GU-74B and GU-84B in SSB linear use and the IMD isnt pretty. Ten-Tec got their nuts in the wringer with the GU-84B.

It looks like the only way I'll get good 6550's for my CE-100V, unless someone here wants to sell me a US made pair, is to get the Svetlana/SED winged C versions direct from Russia or a European seller. And even then I doubt they will last as long as the 1964 TungSols in it now that are down to half power.

[Steve - K4HX]

Do any of those Russian power tubes have good IMD specs?

[N4LTA]

Don't think Marshall wastes their time peddling tubes. They make the best guitar amps in the world and they sell them readily. No one questions Marshalls quality. They have tried several times to get the tube problem off their back using Mosfet technology, but nothing sounds like a tube driven into hard distortion  and that is what Marshall is all about.

[Bill, KD0HG]

I have had terrific results with Svetlana tubes in the past...A quad of 10 y.o. 572Bs in the 30L-1. and a quad of Svetlana 6550s in the stereo amp upstairs. Maybe 15 years on them,.

So the old Svetlana tube manufacturer is QRT? Too bad. I've bought Chinese 833As in the past.. You could shake them and see mouse droppings rattle around inside the jug...

[KC2TAU]

Don't think Marshall wastes their time peddling tubes. They make the best guitar amps in the world and they sell them readily. No one questions Marshalls quality. They have tried several times to get the tube problem off their back using Mosfet technology, but nothing sounds like a tube driven into hard distortion  and that is what Marshall is all about.

Take a look inside of a JCM2000 TSL100,it'll scare you.

[KB3DKS]

Take a look inside of a JCM2000 TSL100,it'll scare you.

You got that right!! I have had a couple of the newer series in the shop recentlyl
They look like they were made in China! Not even close to the build quality Marshall was once known for. Cheap ribbon cable interconnects, not a bit of point to point wiring and poorly made circuit boards.
BTW Marshall has an Accessory line that includes replacement tubes so add that to the buying total.

Yes, the Svetlana 6550s are acceptable. I have never had an issue with them in any SVT, Marshall, or Sunn amp that they were installed in. But that was awhile  ago.
My favorites are still the GEs. The last good JANs were dumped maybe 15 years ago when the Mil ended the contract and took them off the stock list. I believe GE got the contract when Tung-Sol folded.
Bill

[Bill, KD0HG]

WOW!

I just looked up the price of 6550s from online dealers...Original, made in USA GE Owensboro 6550s are going for $329.95? at one web site.

Antique Electronics Supply in Tempe is selling NOS Tung-Sol 6550s for $162.50 each...

They've got 6550s made in the same St. Petersburg plant as the original pre-2003 versions for about $50 a pop...

I've got a factory-matched pair of NOS RCA 6550s. Anyone want to offer me $500 for the pair?

[WD5JKO]

Result: none of them are pumped as long as they should be. That is a major issue with ALL of them today.

SNIP

But vacuum hardness is the worst problem. It becomes especially bad in power pentodes in which the screen grid runs very hot, like EL34s. Nothing outgasses and ionizes that gas as beautifully as a white-hot screen grid. And nothing makes a screen grid hot like operation in a guitar amp, in which the screen is hooked directly to the main plate supply, insuring the screen will be drawing more current than the plate for at least part of the AC cycle.....why?

  I have been working around vacuum systems for 30 years now, and we use cryo pumps to get to about 5E-8 Torr whereas tube factory phots I've seen use diffusion pumps that might get to 1E-6 Torr. This is old technology, but probably fine. If the tube is heated during evacuation (RF Induction), the difference between a 1 hour pumpdown, and a 1 year pumpdown is zero. So what Eric says concerning the short pumpdown is not a factor unless the manufacturers don't heat the tubes. Heating the tubes will force stray molecules, or atoms out of the metals that might later come out when the tube is used. Oils from a fingerprint on the plate could be a factor. Oils from a finer print will not pump out until heated. I recall seeing finger prints on lots of tube plate structures over the years. Assembly people only seem to wear gloves when the supervisor is near, or while wearing the gloves they wipe their face getting the gloves all oily. Once the oil is there, it stays until heated. Best to heat while being evacuated.

  Several years back I made a EL34 based RF linear amp to see what these tubes could do at RF. Not really good RF tubes I might add, but they can be made to play. I had a few overloads from accidents, and 1 good red plate soaking of a Sovtek EL34, and it was done: big time gassy. So whether it was the screen grid, or the plate I don't know, but something gave up a lot of gas. In trying several tube types, the old Genelax Kt77 was low on RF output, but showed no sign of being gassy.

  Adding more volume to the tube bulb allows for more internal outgassing before the internal pressure gets too high. (EH did this to the 7591, switched from the 6V6 bulb size to the 6L6GC bulb size)

  I ended up with the Teslovak E34L with it's bigger bulb, tri-metal plate (30w Pd rating versus 25w for std EL34). It worked well, and I was playing with 20M, struggling to get 30watts or more without a parasitic. Then I keyed up, and the wattmeter said 100 watts! What? Again, I did that, zero reflected power, 100 watts forward. How could this be? Then I looked at the tube, and the entire plate structure was bright orange!! What happened was my grid 2 supply, 300v, failed in a way that the G2 voltage soared to about 450v raising the DC operating point from about 40ma to 400ma. That overload did not damage the tube. I got a pair of E34L's from Penta Labs. Those tubes are brutes.

  Ever since seeing what a E34L can do, I have wanted to play with a bias shift scheme to see if I can harness that power capability I've witnessed during an overload condition.

Jim
WD5JKO

[Bill, KD0HG]

Oh, those EL34s, KT-66 and KT-88s can really boogie.

I have six matched Mullard EL34s available for sale for my retirement fund.

Also...An RCA branded factory matched pair of coke-bottle 6550s. Look like rebranded Tung-Sol 6550s. In an RCA "matched pair" package! "6550-V1"

You name your exorbitant price.

[KB3DKS]

Most audio power tubes will put out RF power. The 6L6 matal have a long history of RF use but how clean are the newer
 Do watch out for China ST shape clones. The chrome base ring is goldish rather than chrome. They might not be around any more, were circa 1994or earlier, but might turn up being passed for vintage T.S. Real gassy, lit up like merc vap.
When going thru the old used T.S. I still have, there seems to be several different types. Side or top getter, plate holes or not, and other small differences. All clearly branded T.S with the 32XXX etc codes. Not sure how many plants they had or where they were. I know one was near Hazleton PA. The 5881s show a similiar variability.

Bill,
Hang on to those old tubes ! Almost as good as an investment in gold 
OT, BTW, did you see that ATT is using your Rule the Air Icon in their 4G promos?

Bill, KB3DKS

[W2XR]

Most audio power tubes will put out RF power. The 6L6 matal have a long history of RF use but how clean are the newer
 Do watch out for China ST shape clones. The chrome base ring is goldish rather than chrome. They might not be around any more, were circa 1994or earlier, but might turn up being passed for vintage T.S. Real gassy, lit up like merc vap.
When going thru the old used T.S. I still have, there seems to be several different types. Side or top getter, plate holes or not, and other small differences. All clearly branded T.S with the 32XXX etc codes. Not sure how many plants they had or where they were. I know one was near Hazleton PA. The 5881s show a similiar variability.

Bill,
Hang on to those old tubes ! Almost as good as an investment in gold 
OT, BTW, did you see that ATT is using your Rule the Air Icon in their 4G promos?

Bill, KB3DKS

Bill,

I think Tung-Sol's main plant was in Bloomfield, NJ, and Bloomfield is a suburb of Newark. They made extremely high quality tubes.

73,

Bruce

[KB3DKS]

Bill,

I think Tung-Sol's main plant was in Bloomfield, NJ, and Bloomfield is a suburb of Newark. They made extremely high quality tubes.

73,

Bruce
[/quote]

Yep got this with Google,
http://vintagetubeservices.com/page16.html
Near the bottom of the page is a print of their locations.
Bill

[W3SLK]

Bill, Sylvania used to have a plant up in Watsontown before they sold it to Zenith. That plant shut down in 1976. Also Thompson had a plant up near the Wilkes-Barre/Scranton area where they were making CRT up until about 5 years ago.