Beam Tetrode EL34s

Lake Placid Blues

Lake Placid Blues

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From Shuguang's data:
http://analogmetric.com/download/Shuguang Beijing Vacuum Tube Datasheet Analog Metric Limited.pdf

Plate power dissipation of EL34-B can reach 30W, whereas EL34A is 25W. EL34-B belongs to tetrode
tube compared to pentode tube of EL34A.
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So the Shuguang EL34-B is actually a beam tetrode instead of a pentode. Shuguang makes two versions of EL34; their EL34A which is a pentode and the B which is a tetrode. A pentode uses an extra grid called the suppressor grid to remove the "kink"*. A beam tetrode or a kinkless tetrode (same thing) uses beam forming plates to funnel the electron stream into a concentrated beam to remove the kink. The big bottle 6CA7 and KT77 are beam tetrode versions of the EL34.

Notice that the description reads that the Shuguang EL34-B can reach 30 watts plate dissipation. These are the dissipation specifications closer to the KT77. The standard plate dissipation for the traditional EL34 and also the 6CA7 is 25 watts. I notice that both the JJ and Gold Lion current production KT77s are 30 watts pd on their data sheets.

Is the Tung Sol EL34-B also a beam tetrode?

I don't think there is a significant tone difference between beam tetrodes and true pentodes, everything else being about the same. I think much of the difference between say a 6L6GC beam tetrode and the EL34 (be it a beam tetrode or a pentode version) is actually the sensitivity ( trans conductance or mutual conductance rating) and other factors rather than them being a beam tetrode or a pentode. Modern 6CA7s sound closer to EL34s than to 6L6s, but many claim that original big bottle 6CA7s sound maybe closer to the 6L6. The modern 6CA7s (such as the EH 6CA7) have a sensitivity of 9-10 matching the original data sheets (Mullard EL34 is 11-12), while original GE 6CA7s have a sensitivity that measures closer to a 6L6 or KT66 (6-7).

* From Doyle
Kinkless tetrode ( also referred to as beam tetrode) refers to the the way a valve characteristic curve kinks as the vale progresses from Class A through Class AB to Class B.
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Re: Beam Tetrode EL34s

You will start to notice a bigger difference between a true pentode and a beam tetrode once signal excursion is high enough. A true pentode will typically draw considerably more instantaneous screen current under those circumstances, which will start to manipulate its operation, as well as place a higher load on the ht lending to more compression.


Regarding tone, the overall tonal balance is really going to be a product of the system as a whole, and the methods in which we misuse the device, not necessarily contained with in the device itself, so the context of "extra low end" is everything, and it may indicate the potential to be able to do something than it actually doing it unconditionally in practice . In other words, it could mean for example the plate z is lower than typically found for the valve type, so it has an easier time with both the 1.7k primary load most people use with an el34, and thus being able to drive potential dips in z with in the low frequency range of any reactive load connected to the secondary. The valve itself won't add what's not there to begin with.

Input sensitively is quite a big deal when we are talking valves.
 
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Re: Beam Tetrode EL34s

I brought this up a while back. I believe that the "Shuguang" 34B, Valve Art 34B and Ruby labeled EL34BSTR and the TAD are all, essentially, the same tubes. I think the "Sino" is as well. I've purchased two pairs of the Valve Art labeled versions from AES (CED). Whatever they are, I like them and they don't cost much. Under 30 bucks for a matched pair. Tubes biased within 2ma of each other, out of the box, with both pairs. The pair that resided in the amp for several months (Marshall "clone") were still within a couple ma when I last checked bias. That doesn't speak to ultimate reliability and longevity, but whatever Apex is doing with their matching is pretty good. And whatever these Chinese tubes are, construction wise, they sound like 34's.

On a side note ... I've been running a pair of current production Svetlana's for the last little while. Not a popular tube and for whatever reason, I couldn't get a pair matched closer than about 5ma out of the box ... factory matched or from a well regarded seller, whom I wont mention by names and I wont buy from again. They sent me the first pair, quick shipping, but 9ma out. Hassled with me by email over how it has to be me or my amp. Finally send me replacement pair which was just under 5ma out (a factory matched pair that I send back was 6+ma out) but the dealer took 2 weeks to replace the first pair despite admitting that they were poorly matched. Personally, I don't think he put in much effort, probably because of lack of stock on hand. At any rate, 3 attempts and best I ended up with was just under 5ma. I suspect that two things are happening ... QC probably isn't great and dealers don't keep much stock on hand. That said, the midrange is what these Svetlana's are about. I like them and think they are better than they get credit for, but probably wont buy another set because of the trouble I had in getting a matched pair. And, last I checked bias, they weren't drifting closer together ...
 
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Re: Beam Tetrode EL34s

Darg1911 said:
I brought this up a while back. I believe that the "Shuguang" 34B, Valve Art 34B and Ruby labeled EL34BSTR and the TAD are all, essentially, the same tubes. I think the "Sino" is as well. I've purchased two pairs of the Valve Art labeled versions from AES (CED). Whatever they are, I like them and they don't cost much. Under 30 bucks for a matched pair. Tubes biased within 2ma of each other, out of the box, with both pairs. The pair that resided in the amp for several months (Marshall "clone") were still within a couple ma when I last checked bias. That doesn't speak to ultimate reliability and longevity, but whatever Apex is doing with their matching is pretty good. And whatever these Chinese tubes are, construction wise, they sound like 34's.

On a side note ... I've been running a pair of current production Svetlana's for the last little while. Not a popular tube and for whatever reason, I couldn't get a pair matched closer than about 5ma out of the box ... factory matched or from a well regarded seller, whom I wont mention by names and I wont buy from again. They sent me the first pair, quick shipping, but 9ma out. Hassled with me by email over how it has to be me or my amp. Finally send me replacement pair which was just under 5ma out (a factory matched pair that I send back was 6+ma out) but the dealer took 2 weeks to replace the first pair despite admitting that they were poorly matched. Personally, I don't think he put in much effort, probably because of lack of stock on hand. At any rate, 3 attempts and best I ended up with was just under 5ma. I suspect that two things are happening ... QC probably isn't great and dealers don't keep much stock on hand. That said, the midrange is what these Svetlana's are about. I like them and think they are better than they get credit for, but probably wont buy another set because of the trouble I had in getting a matched pair. And, last I checked bias, they weren't drifting closer together ...
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Correct, the majority of these tubes are coming out of China are produced at the shuguang factory. "Sino" is a generic term and branding that is thrown on them, it literally just means Chinese.

A matched set is still considered decently matched with in a 5ma difference in idle plate current. Also keep in mind valves are not matched solely on what their reflected idle plate current rests at.
 
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Re: Beam Tetrode EL34s

I think more extensive "matching" can be found outside of the tube dealers who cater to guitar guys. Some of the sellers who cater to the home audiophile crowd do more extensive matching and testing. You also pay for it and the selection of tubes is limited to those considered audiofool approved. That said, I have no way to know how tubes are matched other than how they bias based on idle plate current. Therefore, I accepted the second pair of Svetlana's based on that 5ma "rule". Normally, matched tubes I've gotten have been closer, usually within 3ma ... maybe I've just been lucky.
 
Re: Beam Tetrode EL34s

Darg1911 said:
I think more extensive "matching" can be found outside of the tube dealers who cater to guitar guys. Some of the sellers who cater to the home audiophile crowd do more extensive matching and testing. You also pay for it and the selection of tubes is limited to those considered audiofool approved. That said, I have no way to know how tubes are matched other than how they bias based on idle plate current. Therefore, I accepted the second pair of Svetlana's based on that 5ma "rule". Normally, matched tubes I've gotten have been closer, usually within 3ma ... maybe I've just been lucky.
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That slight degree of mismatch is not necessarily a bad thing, many feel it may add a little more dimension. Personally I don't sweat a 5ma mismatch, it gets a little tougher once it's much larger. For those it does matter to, It would be way easier, and take up much less time to just slightly modify the bias supply to make each feed to the control grids adjustable, than it would to worry about what your getting from the vendor each time. I typically do this with all my stuff, but more so to mix types than for precision
 
Re: Beam Tetrode EL34s

Joey Voltage said:
That slight degree of mismatch is not necessarily a bad thing, many feel it may add a little more dimension. Personally I don't sweat a 5ma mismatch, it gets a little tougher once it's much larger. For those it does matter to, It would be way easier, and take up much less time to just slightly modify the bias supply to make each feed to the control grids adjustable, than it would to worry about what your getting from the vendor each time. I typically do this with all my stuff, but more so to mix types than for precision
Click to expand...

The problem isn't the initial 5ma mismatch. It's that, in my experience, tubes have drifted further apart far more often than they've gotten closer together with use/age. As mentioned, getting closely matched, current production tubes hasn't been an issue in the past, these Svetlana's aside. I don't think I'll modify this amp but in any future build, I probably will add individual bias adjust. Not because of this experience with the Svetlana's but rather because there can still be good deals on vintage tubes sold as single tubes and/or some NOS Eastern European pairs/quads that may or may not be as well matched as claimed. It just adds some versatility.
 
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Re: Beam Tetrode EL34s

Darg1911 said:
The problem isn't the initial 5ma mismatch. It's that, in my experience, tubes have drifted further apart far more often than they've gotten closer together with use/age. As mentioned, getting closely matched, current production tubes hasn't been an issue in the past, these Svetlana's aside. I don't think I'll modify this amp but in any future build, I probably will add individual bias adjust. Not because of this experience with the Svetlana's but rather because there can still be good deals on vintage tubes sold as single tubes and/or some NOS Eastern European pairs/quads that may or may not be as well matched as claimed. It just adds some versatility.
Click to expand...

And certainly less headache.
 
Re: Beam Tetrode EL34s

This one I built a couple of years ago has a low impedance quad bias: it's kinda hard to see but it's on the side of the main board next to the power supply board. It might be a little overkill, but at the time I was more concerned with exceeding the maximum rl for for the control grid should somebody want to mix match valve types and want to use something with a leakier grid without accounting for any extra impedance from the bias supply itself. I doubt I would go that far nowadays.

IMG_3491.JPG
 
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Re: Beam Tetrode EL34s

Nice, from what I can see. But "low impedance quad bias" is beyond me. I know just enough to be dangerous while not electrocuting myself.
 
Re: Beam Tetrode EL34s

Darg1911 said:
Nice, from what I can see. But "low impedance quad bias" is beyond me. I know just enough to be dangerous while not electrocuting myself.
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I used p junction emitter followers as part of the bias adjust, almost like how you would incorporate power scaling in the b+ line. Like I said totally overkill.

If you want a good example of an easy way to put in quad bias, take a look at the power section of the Randall rm100 schematic. From the two I had in shop they worked very well.
 
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