Tubes that can handle 500VDC on screens, or tame the power supply??

[Leo_Gnardo]

Not knowing if the US Tung Sol ever made an EL34, it doesn't really matter to me personally... there is no reason that the Russian Tung Sol (New Sensor) can't make a variety of tubes, new or reissue. But saying this I realize there is a HUGE layer of BS to what tube manufacturers - especially New Sensor, do. One thing that disturbs me is that in one thread, maybe in this one or another thread at a different forum, someone said that Tung Sols are basically made in DIY basements. Then of course I have to wonder how this person knew that and if it is a directly known fact or the result of hear-say. Well, either way....

Much of New Sensor's so-called "variety" comes from applying different labels to the same tubes, making different claims for them and charging different prices. Some of them are OK tubes, others - well you better use them in low voltage applications or else. What "brands" are currently in the New Sensor family? Sovtek, Electro-Harmonix, Mullard, TungSol, GEC Gold Lion. Sound off readers if I left any out. Don't worry, NS's TungSols aren't hand made in some comrade's basement or garage, rather the same factory, same assembly line as all the rest in beautiful suburban Saratov out there in the steppes north of Georgia.

Interesting... never heard of floating the CT. How would one go about calculating the required value of this capacitor

I don't know of any formula but you could start with Ampeg's 0.1uF value, 600/630V. Add extra caps & see whether there's a reduction of hum.

[Chuck H]

Perhaps worth noting...

IMHE (Not: In my "honest" experience as some think, but, In my "humble" experience", as it should be.) the problem is likely occurring at high frequency. Since the typical load for a guitar amp is VERY high impedance at higher frequencies (just look at the plots for this!) and the choke to the screen grids is always limited in henrys it's possible to have very high voltage spikes (and kick backs, thank you cerrem) that find their way through the screen circuit. At these higher frequency impedances it's often possible that the screen circuit represents a lower load than the plates!!! Bumping henries on the choke or adding resistance (in the form of a resistor) after the choke can work. As can bumping the individual screen grid resistor value. Other than that you'd need to mitigate grid drive to reduce spiking. I've dealt with this in builds a couple of times and this is the scenario I interpreted. All of this will change the tone of the amp. for better or worse I suppose since tone is subjective. But I think it's possible that this may be a circumstance to consider.

[Gtr0]

I don't deny New Sensor the right to make tons of different tube types. But you can't reissue something that never existed in the first place.
Justin

No doubt - I didn't mean at all for it to sound snarky.. in fact I appreciate any and all info on these types of things.

AND AND AND... I JUST looked at my supplier and in fact they list it as a reissue - so yes, you are totally correct. I had paid no attention to that when I bought them.

[Chuck H]

And... Even if the "reissue" tube never was, that's not important to the matter at hand. If you like the tube and it's up to the challenge that's more important. Is it up to the challenge? Well the New Sensor data sheet for the el34b (Tung Sol "reissue") is vague, but seems to indicate that the tube is equal to other el34's. That doesn't mean it's safe to exceed the screen voltage as is typical of older amp designs. I don't even know that it's fair to say it's implied by the equivalent specs to older tubes. So there's THAT. My point is, exceeding the screen grid voltage on older el34 amps was common, but that may not mean that new el34's are up to the challenge. New Sensor is notorious for regurgitating info from old tube data sheets. In fact it appears their Tung sol 5881data sheet IS the Tung Sol data sheet with the vintage dates removed. It's also common to find some arbitrary criteria, like voltages for "typical operation", along with all associated performance data at those voltages, etc. that are spot on with vintage data sheets such it's clearly just copied info. It's for this reason that I don't trust modern data sheets that are even a little suspect of not being data acquired by testing the actual tube in question. Because WHY would a tube manufacturer publish copied data if they have actual info on the product they're selling?!? I think these designs are based on the tube models in question and then tossed at the public wall to see if they stick and it's only assumed, by virtue of design copy, that the old data sufficiently matches the new products performance. But are the materials, tolerances and expertise of the new manufacturers equal to that of the old? I do not think so. That basically makes the data sheets cartoons. That is, they look vaguely like real life, but you probably can't safely do some of that stuff.

[cerrem]

And... Even if the "reissue" tube never was, that's not important to the matter at hand. If you like the tube and it's up to the challenge that's more important. Is it up to the challenge? Well the New Sensor data sheet for the el34b (Tung Sol "reissue") is vague, but seems to indicate that the tube is equal to other el34's. That doesn't mean it's safe to exceed the screen voltage as is typical of older amp designs. I don't even know that it's fair to say it's implied by the equivalent specs to older tubes. So there's THAT. My point is, exceeding the screen grid voltage on older el34 amps was common, but that may not mean that new el34's are up to the challenge. New Sensor is notorious for regurgitating info from old tube data sheets. In fact it appears their Tung sol 5881data sheet IS the Tung Sol data sheet with the vintage dates removed. It's also common to find some arbitrary criteria, like voltages for "typical operation", along with all associated performance data at those voltages, etc. that are spot on with vintage data sheets such it's clearly just copied info. It's for this reason that I don't trust modern data sheets that are even a little suspect of not being data acquired by testing the actual tube in question. Because WHY would a tube manufacturer publish copied data if they have actual info on the product they're selling?!? I think these designs are based on the tube models in question and then tossed at the public wall to see if they stick and it's only assumed, by virtue of design copy, that the old data sufficiently matches the new products performance. But are the materials, tolerances and expertise of the new manufacturers equal to that of the old? I do not think so. That basically makes the data sheets cartoons. That is, they look vaguely like real life, but you probably can't safely do some of that stuff.

I have done consulting for New Sensor over the years.... mostly with pedals and transformer designs for their amps... I happen to own two Tektronix 570 curve tracers that I fully restored and calibrated .... I offered New Sensor a great deal ...I would draw up proper data sheets for their product line of vacuum tubes... providing I-V curves , Dynamic transfer curves, Grid 1 current and screen current curves, Ultra-Linear curves....plate curves at all various screen voltages, ie usable data sheets..... I have thermal imaging camera that can give accurate bulb temperatures at various dissipation, to ensure proper tube capabilities.... Well I got a big NO !!!! They are not even remotely interested in having this done....they like their situation just as is ...they don't want to spend a penny...
Whatever... I thinks it pathetic that they want to be a big player in tube distribution but show ZERO interest in providing proper data sheets.... I have seen their "In house" tube tester...looks like a 5th graders science project ....

[cerrem]

Getting back to the original subject at hand.... Last night I blew a power tube in my Ampeg SVT while playing a show..... First time in many many years this happened to me...
The reason is because I put the SVT head on top of the speaker cabinet and I was playing loud and VERY DEEP frequencies !!!
You can see from photo the crack on the tube ..most likely mechanical vibration caused the fracture of the glass, which compromised the vacuum which then provided the lightening show...
I normally stack 2 or 3 SVT heads on a separate dolly and keep it to the side, so not to direct contact with the cabs....
Last night I made exception due to not much room on the stage due to a drummer that takes up 80% of the stage area...
I am thinking maybe the original poster to this thread maybe if he has has amplifier in contact to the speaker cabinet ???

[Leo_Gnardo]

They are not even remotely interested in having this done....they like their situation just as is ...they don't want to spend a penny...
Whatever... I thinks it pathetic that they want to be a big player in tube distribution but show ZERO interest in providing proper data sheets.... I have seen their "In house" tube tester...looks like a 5th graders science project ....

Agreed, that is revealing. And pathetic. I will continue to mostly avoid New Sensor's tube offerings.

[Justin Thomas]

I'll still buy their tubes, but only if they're branded "Sovtek." Cuz despite the "reissues" being unable to hang, that ol' 5881WXT keeps chugging away; anybody know the actual max voltage & plate dissipation ratings on those yet?

Justin

[Gtr0]

And... Even if the "reissue" tube never was, that's not important to the matter at hand. If you like the tube and it's up to the challenge that's more important. Is it up to the challenge? Well the New Sensor data sheet for the el34b (Tung Sol "reissue") is vague, but seems to indicate that the tube is equal to other el34's. That doesn't mean it's safe to exceed the screen voltage as is typical of older amp designs. I don't even know that it's fair to say it's implied by the equivalent specs to older tubes. So there's THAT. My point is, exceeding the screen grid voltage on older el34 amps was common, but that may not mean that new el34's are up to the challenge. New Sensor is notorious for regurgitating info from old tube data sheets. In fact it appears their Tung sol 5881data sheet IS the Tung Sol data sheet with the vintage dates removed. It's also common to find some arbitrary criteria, like voltages for "typical operation", along with all associated performance data at those voltages, etc. that are spot on with vintage data sheets such it's clearly just copied info. It's for this reason that I don't trust modern data sheets that are even a little suspect of not being data acquired by testing the actual tube in question. Because WHY would a tube manufacturer publish copied data if they have actual info on the product they're selling?!? I think these designs are based on the tube models in question and then tossed at the public wall to see if they stick and it's only assumed, by virtue of design copy, that the old data sufficiently matches the new products performance. But are the materials, tolerances and expertise of the new manufacturers equal to that of the old? I do not think so. That basically makes the data sheets cartoons. That is, they look vaguely like real life, but you probably can't safely do some of that stuff.

I have noticed their deceptive datasheets. As if to imply that the new tube *is* the old tube. Perhaps it relays a psychological message to some - one of comfort and security - to know your using solid old school tech, which in this case is a desirable thing.

I have done consulting for New Sensor over the years.... mostly with pedals and transformer designs for their amps... I happen to own two Tektronix 570 curve tracers that I fully restored and calibrated .... I offered New Sensor a great deal ...I would draw up proper data sheets for their product line of vacuum tubes... providing I-V curves , Dynamic transfer curves, Grid 1 current and screen current curves, Ultra-Linear curves....plate curves at all various screen voltages, ie usable data sheets..... I have thermal imaging camera that can give accurate bulb temperatures at various dissipation, to ensure proper tube capabilities.... Well I got a big NO !!!! They are not even remotely interested in having this done....they like their situation just as is ...they don't want to spend a penny...
Whatever... I thinks it pathetic that they want to be a big player in tube distribution but show ZERO interest in providing proper data sheets.... I have seen their "In house" tube tester...looks like a 5th graders science project ....

Wow. As I was reading I was hoping to see it develop the other way... Just reinforces my thoughts above.

It's too bad because it seems EL34s, in general, are generally not reliable. I used EL34 in various amps for almost 2 decades and didn't have a single problem until the last few years. So either they are getting worse or I am pushing the boundries too much... likely a combination.

A few days ago, I saw Dave Friedman say similar things (checked out Tone Talk on YouTube), that it is difficult to find a reliable EL34. But at the current his amps come with EH, but that could be old news by now.

[J M Fahey]

Painting with a VERY broad brush, I trust 6L6 because they have been made since FOREVER (think WW2 ) by Russians and designed/tested/produced for *Military* equipment (donīt think Uncle Vania and his Magic Accordionīs amp were the main focus) ; and a very distant second by their disciples: the Communist Chinese, who were very close friends up to 1965 so must have gotten at least some Technology transfer.
Of course Chinese worry more about cost and huge production than quality control but even so, they have been playing the game non only for long but continuously.

Now EL34 went plain out of production by old game players, Czech/Slovak/Yugo makers were always "second source" at best, and Chinese/Russians never ever made them in the old times to begin with, so the EL34 pond is quite murky.

[Pedro Vecino]

As I understand it for my experience buying tubes in the last 30 years and in relation to the European market: EL34 Tesla (Tesla, not JJ) had similar quality to Philips, Telefunken and RFT. These four are the best. When production moved to JJ they got worse. Same with ECC83 family.
In Russia there was no EL34 (at least in the western market I never saw it). The firsts Russian EL34 I found in the first 90īs (G and G +) were poorly made copies of the EL34 RFT (East Germany).
At that time (a little before) Chinese EL34 were horrible. Marshall used them for a time experimentally in a few JCM800 and as spare for a while for the JCM900 series with a lot of problems. The first JCM900 came equipped with Tesla and when Tesla closed the company, seeing the impossibility of using the Chinese EL34 Marshall redesigned the JCM900 amps for the 6Pi3cE.
The two Yugoslav EL34 (EL34 and 6CA7) were never good and did not have good distribution in Western Europe. The ECC83, however, were distributed in large quantities by National, Edicron, Ruby, Groove Tubes, etc.
The best Russian EL34 was Svetlana, from St. Petersburg. It came to the international market later (I guess it was a new design because I never saw it before) parallel to the launch of the JCM2000 Marshall series.
Thirty years later, the offer has multiplied, both in Russia and China, raising the quality enormously. Today, for amplifiers with 500 or more volts I still use E34L JJ. I think they have the best connection to the original model, which was always very robust. Bogner uses them in Ecstasy (500/520V) with conservative bias settings.
However, EL34 EH, Tung Sol and Mullard (they are different) sound more similar to the old classics.

[Gtr0]

I decided to buy a set of 5881's. So I ordered a quad of Harma from Watford. At best one or two component change in the bias, if any. But I think it will help to use a much more conservative bias as well.

[Roberto]

A note about dropping the screens with a resistor instead of the choke. This will drop voltage on the PI and preamp tubes as well and THAT will likely change the tone of the amp more than the difference on the screens. The following HV rail resistor feeding the PI and preamp in the SLO schematic is a 10k/2W. You should be able to reduce this value to bring the downstream voltage up again. Just measure voltage on the downstream side of that 10k resistor before changing the choke to a resistor so that you have a target voltage.

Another option is to keep the main power supply unchanged, while adding a derivation to supply the screens: from the supply cap after the choke you go both to the resistor that supplies the PI and to another resistor that goes to a cap and to the screen resistor.
This way you can choose the drop across that resistor and, by controlling the two RC values due to screen resistors * cap and "new supply node resistor" * cap, you can control the attack/release of the compression of the pentodes by controlling the dynamics of their voltage.

[Gregg]

In Russia there was no EL34 (at least in the western market I never saw it). The firsts Russian EL34 I found in the first 90īs (G and G +) were poorly made copies of the EL34 RFT (East Germany).

Actually there was a Russian EL34 and it's designation was 6П27Б (6P27S) but even in the Soviet union they were unobtainium because only 5000 experimental pieces were ever released. Obviously they were not able to nail them from the beginning.

[Pedro Vecino]

Actually there was a Russian EL34 and it's designation was 6П27Б (6P27S) but even in the Soviet union they were unobtainium because only 5000 experimental pieces were ever released. Obviously they were not able to nail them from the beginning.

I have never seen it. But in the data sheets it says that itīs a output beam tetrode.
https://rudatasheet.ru/tubes/6p27s/