Modern EL34 reliability?

[Enzo]

Plus "Svetlana" tubes here in the USA are not from the Svetlana factory, they are a product of the Sovtek family.

[bob p]

That Mullard video was fantastic. thanks for posting it.

Here's a vintage theatre filmreel by Mullard that was used to advertise their tubes.

One of the actors in the video ended up becoming the Third Doctor Who.

[drewl]

FWIW, just got in a TSL100 for a tune up I worked on four years ago.
It had the wrong 220k bias resistors but a transitional PC board that is not breaking down.

The EH EL34's I put in four years ago are still holding steady screaming around 135w into a load resistor.
He wants the same replacement tubes so I'll see if they still can hang.

[soundmasterg]

Plus "Svetlana" tubes here in the USA are not from the Svetlana factory, they are a product of the Sovtek family.

That wasn't always the case. Too bad for Svetlana in St. Petersburg that they didn't realize sooner that the rights to their name in the US and Canada was controlled by their US distributor that went out of business, thus allowing Mike Matthews to swoop it up and use it for his Saratov factory tubes.

Greg

[Chuck H]

FWIW, just got in a TSL100 for a tune up I worked on four years ago.
It had the wrong 220k bias resistors but a transitional PC board that is not breaking down.

The EH EL34's I put in four years ago are still holding steady screaming around 135w into a load resistor.
He wants the same replacement tubes so I'll see if they still can hang.

That amp may clip predominantly in the preamp and not clip the power stage much. Did you test for this? Is that 135w of sine or when clipping? What is the plate voltage? I did notice the amp uses a very un-Marshall like 280r resistor rather than a choke between the plates and screens, 5.6k grid stops and high Vp on the PI.

[bob p]

That wasn't always the case. Too bad for Svetlana in St. Petersburg that they didn't realize sooner that the rights to their name in the US and Canada was controlled by their US distributor that went out of business, thus allowing Mike Matthews to swoop it up and use it for his Saratov factory tubes.

It's a problem when old world business managers don't have the foresight to value new world markets. There's been a 100-year legal dispute between the Czech company Budejovicky Budvar and Anheuser-Busch InBev over the Budweiser name.

In Europe, beers are often named after the towns where they originate. In German, "Budweiser" means "from Budweis", the German name for the Czech town of Budejovicky. In Europe, "Budweiser" means the beer from Ceske Budejovice, Czech Republic. In America, it means the Anheuser-Busch InBev product, solely because the first use of that trademark in the New World was for the Adolphus Busch product. As both brands have gone global they've been fighting over trademark rights all over the world.

It definitely creates confusion, especially if you consider that Adolphus Busch's original intent was to copy the Bohemian Budweis product and sell it in America.

Where a Budweiser Isn't Allowed to Be a Budweiser | TIME.com

[tubeswell]

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

Yes it did. I used 270k (on the bottom leg of the voltage divider) in the end and got 350V at the node between the stacked caps (for testing a bunch of fresh tubes to get a decent matching set at a safe screen voltage).

[Chuck H]

You can also use a zener (or a string of zeners) to drop the screen supply. They won't cause additional sag over the standard resistance.

[bob p]

I had a few thoughts about the EL34 reliability problem:

1. Are you guys talking about 50W or 100W Marshalls or both? In another thread Chuck had mentioned that the best sounding amps tended to be those that have the "wrong" bias feed resistors in them -- high powered amps running parallel pairs of power tubes that didn't have their bias feed resistors adjusted for the decreased impedance. I was wondering about those amps having thermal runaway problems because those resistors are supposed to be downsized in parallel output situations to prevent thermal runaway, and Fender did that but Marshall didn't. Just wondering if there might be a connection to Marshalls eating up EL34.

2. Another thing that I had thought about was the potential for differences between new production and yesterdays' EL34. We had discussed the idea that maybe the current producers just weren't building good tubes because the Golden Era knowledge on how to build them has become lost. Essentially, we were blaming today's producers for not knowing how to build tubes to meet/exceed their spec sheets.

It has crossed my mind that perhaps they're not even trying to build tubes the way they used to build them, where they were built to exceed all of their specs. Maybe the current tube manufacturers aren't looking at the old manufacturing recipe; maybe they're looking at spec sheets and building to meet the spec sheet rather than to meet the old-world exceed-the-spec-sheet type of performance. Maybe it's not the knowledge of how to build that has become lost ... maybe it's the desire to over build them that has become lost, such that they're now building them to meet the data sheet specs rather than to exceed them. If that's the case it would explain why today's EL34 seem to meet their specs but fail when you really pound on them like we're used to doing with the old EL34.

3. ROHS. I just noticed an ROHS marking on a new set of tubes. I had always thought that vacuum tubes wouldn't be part of of the ROHS initiative. I haven't looked into ROHS compliance yet, so I thought I'd ask -- is there anything in the ROHS manufacturing standards that should effect vacuum tubes? I would have thought that vacuum tubes would never be able to earn an ROHS stamp. I'm wondering if ROHS compliance might result in the new tubes having no chance of being as good as the old ones.

[g1]

ROHS compliant solder for the pins? (power tubes only)
How about materials used in the getter?

(both items I think may be subject to ROHS but have no effect on reliability or performance)

[soundmasterg]

I had a few thoughts about the EL34 reliability problem:

1. Are you guys talking about 50W or 100W Marshalls or both? In another thread Chuck had mentioned that the best sounding amps tended to be those that have the "wrong" bias feed resistors in them -- high powered amps running parallel pairs of power tubes that didn't have their bias feed resistors adjusted for the decreased impedance. I was wondering about those amps having thermal runaway problems because those resistors are supposed to be downsized in parallel output situations to prevent thermal runaway, and Fender did that but Marshall didn't. Just wondering if there might be a connection to Marshalls eating up EL34.

2. Another thing that I had thought about was the potential for differences between new production and yesterdays' EL34. We had discussed the idea that maybe the current producers just weren't building good tubes because the Golden Era knowledge on how to build them has become lost. Essentially, we were blaming today's producers for not knowing how to build tubes to meet/exceed their spec sheets.

It has crossed my mind that perhaps they're not even trying to build tubes the way they used to build them, where they were built to exceed all of their specs. Maybe the current tube manufacturers aren't looking at the old manufacturing recipe; maybe they're looking at spec sheets and building to meet the spec sheet rather than to meet the old-world exceed-the-spec-sheet type of performance. Maybe it's not the knowledge of how to build that has become lost ... maybe it's the desire to over build them that has become lost, such that they're now building them to meet the data sheet specs rather than to exceed them. If that's the case it would explain why today's EL34 seem to meet their specs but fail when you really pound on them like we're used to doing with the old EL34.

3. ROHS. I just noticed an ROHS marking on a new set of tubes. I had always thought that vacuum tubes wouldn't be part of of the ROHS initiative. I haven't looked into ROHS compliance yet, so I thought I'd ask -- is there anything in the ROHS manufacturing standards that should effect vacuum tubes? I would have thought that vacuum tubes would never be able to earn an ROHS stamp. I'm wondering if ROHS compliance might result in the new tubes having no chance of being as good as the old ones.

Back in the day when tubes were used for all electronics there was a lot of pressure on the companies who made tubes to make the best quality tubes that they could, especially if they wanted military contracts. With modern electronics mostly leaving vacuum tubes behind in the rush to solid state, the economic incentive to make super good quality tubes just isn't there and likely will never come back. They make them just good enough mostly these days. The biggest slip in quality when compared to old tubes is in the cathode materials and metallurgy, and in the amount of time they leave it on the machine to get a hard vacuum. At the onset of tube electronics they figured out in short order that the presence of impurities and trace gases inside the tube envelope kills the cathodes prematurely, so a good vacuum is very important. A lot of the knowledge was lost as companies closed and people died off. the Svetlana factory in St. Petersburg probably has the best knowledge available and could and did make the best modern tubes but they stopped producing receiving tubes because the market just wasn't there for them.

Another thing is many of the Russian sourced tubes that we use today were a variation that they made over there that was used by them in regular production and consumer products, but it wasn't quite the same as what we had. It was close enough in most cases though so they relabed it as a 5881 instead of whatever model it was for the western markets and it worked but didn't sound that nice compared to our NOS 5881's. They tried that also with the 6V6 and EL34 and the ones that they initially used were greatly inferior to the original types so those Russian manufacturers had to make better and more accurate tubes to the types that the West used. The original Sovtek 6V6 and EL34G that were the not so accurate ones were particularly bad. Later they came up with better alternatives. Another example even though it isn't Russian is the JJ 6V6. It isn't really a true 6V6...it is more like a 6L6 in a lot of ways and probably came from some sweep tube that they used that JJ modified, but it is close enough and it helps that it has such high voltage ratings.

The El34 being a true pentode and a softer vacuum tube will never be as reliable as a 6L6 or 6550, and with today's tubes being poorer quality than old stock stuff, people need to make circuit design changes that take that into account or risk their tubes not handling the conditions.

Greg

[tubeswell]

I had a few thoughts about the EL34 reliability problem:

1. Are you guys talking about 50W or 100W Marshalls or both? In another thread Chuck had mentioned that the best sounding amps tended to be those that have the "wrong" bias feed resistors in them -- high powered amps running parallel pairs of power tubes that didn't have their bias feed resistors adjusted for the decreased impedance. I was wondering about those amps having thermal runaway problems because those resistors are supposed to be downsized in parallel output situations to prevent thermal runaway, and Fender did that but Marshall didn't. Just wondering if there might be a connection to Marshalls eating up EL34.

Yes the 1959 Superlead 100. I have another 'handwired' reissue SL100 in at the moment. The Marshall 'designers' have blindly copied a mid 60s schematic without thinking about operational requirements. The last guy to twiddle with the bias had left the bias crazily biased at something like 60mA with 480V on the plates. Turns out you can't get the tubes to bias properly without changing the resistors in the bias supply. I had to swap out the 27k bias feed resistor for 18k to get the bias voltage close to -48V. I might have to go to 15k to get it hovering around -50. Of course this means its not wired to 'original spec' anymore, but then again the type of tubes available today don't seem to be able to handle the 'stock' circuit.

[bob p]

I should have typed "grid load" instead of "bias feed" in Post # 99. It's too late to change it now.

Yes the 1959 Superlead 100. I have another 'handwired' reissue SL100 in at the moment. The Marshall 'designers' have blindly copied a mid 60s schematic without thinking about operational requirements...

This is the thread that I was referring to, when I mentioned a discussion with Chuck in my previous post:

http://music-electronics-forum.com/t44784/#post461760

I know this is heresy, but here goes: If the quad-EL34 handwired original-spec amp is running with 220k grid load resistors, I think operating conditions would improve if you cut the value of those in half and adjusted the bias circuit accordingly; those over-value 220k grid load resistors definitely aren't helping to prevent thermal runaway. When going from a single-pair to a dual-pair output section those grid load resistors supposed to be downsized by 50% to prevent thermal runaway. Marshall doesn't do that, for whatever reason. IMO paying attention to proper grid loads might help with the runaway problem.

[bob p]

FYI here's a copy of my post in that other thread:

... I won't argue that the grid load should be adjusted for the driven load. I completely agree. I've even said as much already. I was only noting that there are some coveted designs that failed to recognize this design element and the resulting manifestation of "improper" design has been well received tonally by players. Not sure how much more discussion that deserves, but it is something that could go unnoticed (or at least unmentioned otherwise).

I alluded to this in the EL34 reliability thread. I think it's worth discussing.

One function provided by the grid leak resistors is to provide a leakage path away from the grid to the cathode when the grid gets heated, emits electrons and becomes positively charged. As the grid gets hotter it emits more electrons and anode current increases. This can create a vicious cycle in which heat causes more anode current, which causes more heat. When the bias drifts out of control we end up with thermal runaway and failure.

Essentially, a properly sized grid leak resistor will allow sufficient leakage path to the cathode that it pulls the voltage of the grid back to a stable value.***

When you add an extra pair of output tubes the effective parallel impedance is cut in half, so you can cut the value of the grid leak resistors in half without loading down the previous stage. Decreasing the grid leak resistance has the beneficial effect of allowing more current to leak to the cathode, neutralizing the charge on the grid and helping to prevent thermal runaway.

Based on the chart above I see that Fender didn't bother to make these adjustments in the Tweed era, but they were smart enough to make these adjustments in the BF/SF era. Marshall on the other hand, never made these adjustments and we see Marshalls having the nasty habit of going into runaway and sacrificing tubes. If I had one of those tube-eaters, I'd be adjusting the grid leak resistors by cutting their value in half. Who knows, it might fix the EL34 reliability problem. Worth a shot anyway.

*** It would be interesting to know if the grids are being carried positive in the Marshalls that fail.

[pdf64]

...The El34 being a true pentode and a softer vacuum tube will never be as reliable as a 6L6 or 6550...

Is the vacuum spec of EL34 really different to beam tetrodes etc?
I thought that claim was another example of Aspen Pitman's nonsense technobabble.
Surely if the vacuum wasn't good the getter would get all used up quickly and the tube fail?