Chinese tubes

[lowell]

I bought some Chinese 6L6 tubes from Tubes and More. I figured I'd give them a shot at $5 a piece (dealer pricing) instead of the trusty JJs. FYI I think JJ tubes are incredible. I know some people have been complaining about them lately, but I love 'em. I have them biased to 70% and fixed bias just like my JJs were. Anyway I believe I'm hearing a boost in mids with these Chinese tubes. Sounds to me like it's around 1k, as I'm getting more of that annoying "thack" when I pick a note. Has anyone used these or have any opinion on their tone? Just curious.

[tubeswell]

Are they the Chinese 6L6s that look like Russkie 6P3S internally? (I think those are 20W tubes and they don't handle above 400V on the plates - or at least I had some at 450 and they didn't last long)

[lowell]

Probably not. These are them More Info for item T-6L6GC--CHIN

[tubeswell]

Well they look veerrry similar internally.

6L6 = 6L6GT = 6P3S tube. Output tetrode.

[greekie]

I feel the same about picking up chinese and russian tubes as I do when picking up women in a bar or a club - given you pick the right model, it's all about quality control!

;-)

[Pedro Vecino]

I know the older version (black/brown base with grey plates). These tubes were used by Mesa (STR 420) for a while. Coinciding with the launch of the first Dual Rectifier. It´s easy to confuse with 6Pi3C (similar structure) but are different.
Basically sounds good, but narrower. Mechanically they are more fragile than other 6L6 and with shorter duration.
To me it sounds better than 6Pi3C. With less compression and more linear. But I refer to those produced previously. These black plates I d´ont know (Probably are very similar).
Regards

[lowell]

I do know that TAD, Ruby, and HT all are hand selected Chinese tubes. I think that testing and hand selecting is the key to a reliable tube. That being said, I notice a tonal change for the worse with the Chinese tubes I have. Again that's my opinion as someone else might prefer a smaller frequency response and more pronounced high mids. My question is more if anyone's noticed the tonal difference, not reliability so much.

[greekie]

I do know that TAD, Ruby, and HT all are hand selected Chinese tubes. I think that testing and hand selecting is the key to a reliable tube. That being said, I notice a tonal change for the worse with the Chinese tubes I have. Again that's my opinion as someone else might prefer a smaller frequency response and more pronounced high mids. My question is more if anyone's noticed the tonal difference, not reliability so much.

Ah, yes, I agree with you. The high-mid fizz can get very annoying! I try to distinguish between the different models that are actually made in China. Much of it is rebranded as this and that, but there are some models that stand out from the crowd. Like the Mullard-style tube offered from TAD and Harma. If you get one that isn't microphonic, it sounds very much like a good american NOS tube - GE and RCA come to mind.

Jake

[km6xz]

Testing and selecting is part of the process of re-branding of course but Ruby and probably all of them use tubes from Russia and China for the bulk of their tubes.
I am not sure where he idea that any of these tubes have a restricted bandwidth, any functional receiving tube, has a gain bandwidth product far into the low VHF frequencies. When plugged into a particular circuit the circuit and tube combination might exhibit different system transfer functions than another tube in that same circuit, but the tube itself has nothing in it that would have a characteristic sound. Find something you are pleased with and stop looking. Your amp, in its current state of operation, combine with that particular tube, might have a sound you like but changing anything will introduce differences that will swamp any imagined differences in tubes. A tube you like in your amp might be not to your taste in another amp, even of the same model. There are too many variables attributed to tubes that really are beyond the control of the tube. But it sells a lot of tubes, and some get recommended when as sounding a certain way when it only does in the single individual amp the reviewer heard.

When run in its intended design parameters for operation, there is VERY little difference that can be measured or heard in blind testing between tubes of the same spec. In guitar amps, the sound difference people are usually referring to is the overload harmonic generation, when the tube is highly stressed. Clean at levels well within design spec, there is very little difference. When overloaded, the rest of the amp has even more to do with the resulting sound, such as differences in recovery from the power supply or output transformer saturation...and most of these stress related differences are more influential over the sound than any tube. A tube sound can not be separated from the operating environment, it really has no sound without the total system.
One problem with tube production or rebranders is testing is very limited, most set up a test jig, with a HT supply, a plate transformer and measure static cathode current, and calculate Transconductance. That tells something about the conduction characteristics at the operating point they arbitrarily selected but it will have little connection with what your amp and that tube does as a combination. As a result of that ambiguity, mu advice is to just find something you like and stick with it but do not recommend it to others unless they have the exact same amp, speakers, mains voltage, playing style, etc etc because what you are hearing that you like is a function of all those things and says nothing about how they "sound" in another amp with a different playing style or environment.
It is too bad more testing is not done, because more information would be available as to real specs of the tubes offered now labeled 6L6 or EL34 etc.
I just shipped my curve tracer to Russia last week, it is supposed to be here mid week. I packed up more of my US based test instruments, brought a HP spectrum analyzer and HP wave analyzer, and some lab type meters packed in luggage on my flight from San Francisco yesterday. I also brought a pile of 6L6 Ruby tubes got when I visited them in Petaluma Wednesday. I am going to start testing for fundamental specs of the various Chinese and Russian tubes so I have basic specs to design around. I have been working on a rapid test curve plotter for printing a family of curves referenced to serialized tubes, individual serial numbers assigned to tubes so they can be tracked for longer data.
Since the tube companies do not test specs that are meaningful to engineers or designers I figure this is a first step in reducing the confusion and mythology that has sprung up in its absence.
For example the posted specs of the 6п3с and 6п3с-е have nothing to do with either of those tubes. The inter-electrode capacitance, max anode potential, dissipation, even heater current are wrong, and were created the way they were for political purposes more than engineering, decades ago and never changed.

[tubeswell]

Hi km6xz

I'm curious about the similarities between Chinese 6L6s and Russian 6P3S and JJ6V6S. The plate structures look similar. Do you happen to know if the 6P3S for example would run like a JJ6V6S (I.e.: into the same kind of load at the same kind of voltages)?

How long do tubes really last?

[km6xz]

The 6п3с is very similar in characteristics to 6V6's but more so, higher plate dissipation for example, more of a less potent 6L6 such as a 6L6GT. They are not as rugged as the 6п3с-е which is often called a 5881 but it is not quite that either, being a more powerful tube. The useful anode voltage both the c and c-e is twice the rated spec. To give an indication, the 6п3с can survive moderately well in a Jim Kelly amp calling for 6v6's that just are not available anymore that can handle them.
I am sure the JJ is patterned after, and even has the same jigs for production as the Soviet design 6п3с since it was an extremely common tube within the Soviet Block use by the millions in everything from TV sets to military communications equipment. There were whole experimenter clubs of home hobbyists devoted to the tube that found its self in amateur radio receivers and transmitters, hi-fi gear, test instruments, even studio strobes for photography. Sort of the 741 of tubes...
The big brother to it, the 6п3с-е is usually thought of as a ruggedized version but it is a different tube. The naming convention only considered tube configuration for the 6, and the п( "P" in sound in Cyrillic), and the number 3 was just the design order. The suffix would relate to reliability factors such as vibration tolerance or guaranteed service hours.
If I had a 6V6 amp, I would not hesitate to throw a couple 6п3с's into it.


How long do tubes really last? About the same variability as the answer to "how long do people last";>) There are tube uses and there are tube abuses, if any tube is kept within its design parameters it last a long time, many years. I have an old Tektronix 570 curve tracer that was build in the early 60s that still has 90% of its original tubes and works perfectly. That includes the power tubes in the pass regulator. I have some 6080s in a regulated lab power supply that still meets specs and those tubes were last changed in 1967 and was used everyday for decades after that. Were the tubes super tubes? No, they were just run conservatively as intended.
But conservatively run tubes in power amps sound too normal, low harmonic generation so in guitar amps that would never do. Tubes only sound really good when driven well into non-linear portions of their curves, overloaded. So getting reliability and getting desirable tone are two opposing requests, pick one. It is certainly possible to create amps with super duty RF type tubes run in a non-linear fashion that would last longer than the player but that does not seem to be a popular consideration. I've build amps using 3cx300's that could loaf at 600 watts of dissipation for many years of operation. But they only sound "guitarish" when intentionally operating outside their design parameters, in this case either overdriving(not likely unless power supplies and loads are house sized) or operating in low voltage non-linear conditions. Something to play with.

[tubeswell]

If I had a 6V6 amp, I would not hesitate to throw a couple 6п3с's into it.

So that is, with a ~3k3-6k6 load resistance I presume? (and allowing for the bigger draw on the heater winding)