Well, I would bet that raised some eyebrows! Seriously, there is yet another ongoing debate on one of the audio sites. This 6L6 sounds better than that 6L6.

So, if there is a different "sound" in between two 6L6s, do you think that maybe it might just be because one brand is made different than the other which changes the effective bias point (read incorrect application) on the conduction scale? I will bare my thoughts and will certainly be subject to criticism no doubt. I am not into boutique coupling capacitors and I will not even think of buying a Western Electric 350B which is purported to be the "Holy Grail" of 6L6 tubes (for somewhere around $600.00 each.

I know that many of the members here are engineers and therefore are capable of discussing the differences with informed opinions.

So, the questions are:

1) Is there a difference given that the tube is what it is labeled. Don't compare a 6L6 with a 6L6GC. That defeats the question. Talking about a circuit that is designed for a specific 6L6 variant and that the correct tube is installed.

2) Could there be a difference because the "auditioneers" are actually putting in a tube that is now not properly biased due to circuit requirements?

Hope that rambling made sense. If not, please feel free to ignore this thread!

The 6l6 family is downward compatable, that is a 6L6GC can sub for a 6L6 GB, 6L6GA, or the metal 6L6. Not the other way around in most cases. The "C" is the latest "official"designation, and the hardiest. Most recent production should be able to match 6L6GC specs. Also the 5881 can sub for any of the above.

I used some re-issue Tung Sol's recently with success, the recent Shuguang's are pretty good too for moderate duty.
As for the inexpensive subs sold, some are great, some not so good. Order 4, 2 or 3 good enough.

As for vintage, RCA, Sylvania, Tung Sol are all good, but getting scarcer and pricier, no matter OS or used.

In the end, the original specs of whatever the set is should give you an idea of what kind of load the tubes are expected to handle, so you know which league you need to be in. I have a few audio amps that sing on metal 6l6's that can often be had cheaply, but put them in a Fender, and have the fire extinguisher handy. Enough?

I would love to see actual technical reasons why one tube "sounds" different than another of the same type.

Characteristic curves or SOMETHING! Technically, they should be the same.
Maybe biasing is different, maybe inter-electrode capacitance is different, but even that shouldn't have much bearing in audio circuits.

I'm planning on building a 6L6 stereo amplifier with Edcor audio transformers. I expect to produce about 20 watts in Class A.
Which, I plan to use this unique design which is self inverting and uses an LM317 current regulator, so it can only work in Class A.

http://diyaudioprojects.com/Tubes/KT77- ... -Tube-Amp/

As I have a bunch of 1625 transmitting tubes as well as a bunch of 6BG6G Horizontal output tubes, both of which are 6L6 derivatives. As are 807s. I hope to make it somewhat universal with socket adapters and switchable heater voltage. I'm curious to see if there is any difference in performance with different 6L6 class tubes.

I'm betting with correct bias, there isn't

-Steve

Still on. Not a nickel's worth of difference, as long as you obey screen voltage maxes. All great platforms. Hint: don't ever try to get the theoretical 50+ watts out of any of these for any period of time, unless you have a caddy of spares.

I like the 807 a lot because it is majestic, or the 1625 because it is inexpensive if you have a correct filament winding, and I have tried the 6BG6/6DQ6 etc beam tubes more than once.

I'm only hoping for 20 watts Class A. I hope that isn't pushing them too hard.

50 watts wouldn't be possible unless running Class AB2 or B. Then I bet slight imbalances and characteristics WILL make one tube sound different than another. Things get critical in Class B.

-Steve

I did make one using 1625s, don't think I got 20 watts out of it, but it does sound good.

I like to ones that test GOOD on my B&K 700!

DR BILL

It isn't in the sound. It's in the quality of the tube. The G styles tend to last longer. In fact, the GC's are the ones I'd least trust. That is after the metal ones.
I agree you aren't going to get 50 watts out of a single pair of them.....
Too small a package-over heating. Burn out.
Bill Cahill

The technical reason is that the characteristic curves aren't the same, even from the same brand from the same batch, and sometimes not even close from brand to brand (depending on how you define close). The gain is all over the place, for instance, +- 20% or more. The construction of the tubes varies wildly from brand to brand and part to part. leading to pretty big differences in the capacitance and the sensitivity micropohonic effects are closely related to the physical construction of the tubes. Compare different brands of 12AX7 some time, a Telefunken has plates most of the length of the tube, a JJ is about 1/4 of the length of the tube. The Telefunken is demonstrably more microphonic, just tap the envelope and listen to the nice ringing sound.

One of the important design goals is to make the design less sensitive/insensitive to the variations of the of the part. Bare amplifying devices tend to have massive tolerances. Tubes are probably the best in this regard. Check the tolerance on the beta of transistors or op-amps - Having a range of beta from 20-100 on an individual transistor is common. Amplifier design needs to take this into account, it's one of the more important factors. That's a good reason you use feedback - because it makes the system gain less sensitive to the gain characteristics of the tube/transistor/op-amp, etc. Vacuum tube power amps are not very good at handling varying gain of the output tubes, - push-pull with feedback is better in that regard, for instance, than an SET. Some of the minimalist SET amps don't to anything to alter the sensitivity and the sound is entirely dependent on the individual parts, regardless of how they differ from individual tube to individual tube, aging, temperature, etc.

So different tubes to result in different sound in audio amplifiers, for very good and easily objectively demonstrated reasons. It's not all audiophoolery.

I know it's fun and all (and nobody give them more hell than I do in the right venues), but don't underestimate the ability of the "golden ear" people or other more rational but experienced individuals to be able to hear differences between equipment. There are clearly audible differences that almost anyone can hear if they know what to listen for. Where the golden ears usually go so horribly wrong is the explanation for how and WHY it's different and what is causing it. That's where the real arrogant stupidity, and the gibberish terminology usually comes in.

I have been down this road for 25 years, and there's no doubt that the audio *industry* depends, for large part, on snake-oil nonsense sold to people who have a psychological/social need to buy it, not about accurate audio reproduction. But there are certainly very real engineering problems to be solved and there are very real engineering differences that people can easily detect.

Brett

p.s. edited to fix the spelling and grammar, wow, must have had some misfiring neurons going on there...

Well if you have a nice set of vintage 6L6 tubes, you can sell them for guitar amps and make a tidy profit, regardless of what you think of the sound. Now for another debate-alot of old ham transmitter projects used a 6L6 tube for the output or even a driver in high power rigs. So has anyone rolled tubes in their 6L6 based transmitter, and critiqued the results? This one makes the keying sound smoother, this one gives one more S unit at the other station, this one is more pleasant to hear, etc.

Some of the older Heathkits used KT-66 (7581) which is in the 6L6 family and they sounded pretty good.

I get the sense that I may be on the same page as you guys. It just gets me how some people are so hung up in "black plate" and "gray plate" etc. One of the things that I was trying to explore is that maybe, some of the tubes that are labeled as a 6L6 are actually something else that was close and some entrepreneur saw a revenue stream and re-labeled or re-based them, sold them as a 6L6 and that is why some versions "sound" different. They ARE different to the point of maybe even being not correct. Surely, Tube A needs different bias as Tube B for instance. And inter-electrode capacitance may surely enter into it. Different tubes need different impedance for the output transformer.

As for the 807 and the 6BG6G, you guys hit right on target. I fully intend to build a nice 6L6 amplifier using either of those two tubes. I have several of both types. I am not going to get into the LED indirect lighting thing and chrome plated transformer bells etc. but I just want to explore something different. A good 6L6GB based amplifier should fit the bill I think. And instead of 12AU7 or 12AX7 tubes in front of the 6BG6 will be 6SN7 or 6SL7 tubes. I did notice that they are not just drop in replacements. But could be close.

Go one step further, how about Push Pull 7C5 tubes instead of 6V6, and 7N7 in place of the 12AU7 and 7F7 for the 12AX7. Well, sorry I have strayed from the topic. Please keep the opinions coming about how this tube (same number) sounds different than that tube (same number)...

HH Scott made an amplifier, 296, that uses the 7581. They are rather expensive shall we say!

Check this out!

http://www.nj7p.org/Tube4.php?tube=7581

I guess there is no "official" criteria for labelling tubes. I've seen all these oddball foreign types with crazy numbers like 6L6XYZ-EH which suggest that they are related to a 6L6. I could brew up some in my basement that have the same basing and call them "better equivalents to the 6L6". And given that practice, of course Brand X is going to sound different than Brand Y because they aren't the same tube!

They put out a 7591XYZ which was a joke. You had to change the bias resistors in the circuit etc. It was most likely a re-pinned 6L6. A lot different than a 7591! I will admit that I use a Soviet Military Surplus version of the 7189 (6П14П-EB). Very happy with them and they are excellent tubes and not some BS stand-in. And, I recently, I bought 8 6P3S-E ( 6П3С-E ) Military Surplus tubes. I have to say that they test good as a 6L6 but have not installed them in any circuit yet. Sometimes marketed as a 6L6GC but more like a 5881.

Hmmmm how about the silicon rubber tube dampers? I guess I missed the boat on them. They seem to sell like hotcakes.

Here are two tube amplifiers I built. The first one uses 6T9 Compactrons in Push-Pull and is capable of a little less than 10 watts per channel. The other is an experiment with 25L6G tubes and is worth about 6-7 watts per channel.

Both of them are wonderful performers and I really enjoy listening to them! The 6T9 amp seems to work best with a pair of Japanese made bookshelf speakers sold by Olson Electronics and the 25L6 works best with a pair of Fisher XP55B speakers.

Nothing exotic used here. Just fun building stuff

The 6T9 uses Hammond output transformers and the 25L6G amp uses Edcor brand output transformers. I highly recommend Edcors!

-Steve

Forget it. "Sounds" is on the imaginary axis.

RRM

Isn't that the truth...

Steve,

Both of those amplifiers look very nice. Surely there are gobs of Loctal and Compactron tube out there the go for a song and are excellent performers. Compactrons were designed and produced at the zenith of vacuum tube manufacture. Excellent, excellent construction, design and performance. Horizontal Output Sweep tubes would make very powerful audio amplifiers. I guess the output transformers would be the expensive part of construction...