Sonic qualities of SET output tubes?


Can you readily identify a 300B, 2A3, 805, 211, etc., amp’s sound with your eyes closed most of the time?


If so, I’sure would like to hear from you.


Amplifier design and the technology utilized within its confines decides the ‘voice’ or influence it will yield as much or more so than merely the output tubes the designer has chosen to use.


I get that part emphatically. One must hear the amp regardless the type of output tube technology on hand.


And yes, some Pentodes and Tetrodes are used as Triodes but are not indeed triodes by their specific architecture. That’s OK, just focus on their use as Triodes herein, please.


There are however certain tube types, irrespective of vintage which have basic undeniable sonic colors or characteristics, apart from their electrical aspects which keep attracting people to amps which use this or that tube in its output stage.


Some love 211s. some adore 300Bs. Some love EL34s configured to run as Triodes. I have an affinity for the latter. So far anyway. This topic could change my mind.


Has your own experience informed you what this or that output tube’s natural flavor regularly announces itself to be so you can have a reasonable expectation of its general presentation?


What sonic attribute continually attracts you to a particular SET tube design, 300B or some others?


Or, conversely, what is it about the sound that would bring you to covet a 211 amp over a 2A3, for example.


Why as another example, would you pick a 2A3 amp over one using 805s or 300B, 211, etc. or vice versa?


Removing ‘vintages’ and electronic or electrical qualities from the argument, what sonic attributes for the more popular S.E.T. amp output tubes have you determined seem to persist in their particular DNA?


I’m asking for input from those SET tube devotees to lend their experiences and knowledge on the subject of what tube sounds like what irrespective of the SET application, generally speaking.


My goal is to try getting a better feel for which SET Tube amp design, if any, I’d want to pursue and possibly invest heavily into going forward as the soul of a new system.


Tremendous thanks to all!

blindjim
Inna > I mentioned LAMM and Wavac.

Blindjim > huge thanks Inna can’t say how much I appreciate all your feedback. yes, you sure did. I’ve been reading furiously on every suggestion, and all the technical data. I am getting confused with all the input I’m gathering, though I do have notes on nearly everything so far.

Saw at least one LAMM amp needs manual biasing. For me that’s a deal breaker. Its ticket is another I suspect, for now at least.


Grannyring > Did you buy that set of Thor TPA30s on Audio Mart?

Blindjim > sorry man, no. Not able yet to do anything worthwhile yet. Still waiting.
Yep. Bone stock, they were the best sounding little goobers I’ve heard to date, and on run of the mill Eff spkrs. That sound is why I bought the TPA 1000 Mk II line stage, and those VR4 JR spkrs. Although not in that order.

If or when possible, I’d buy them or the 60wpc versions in a heartbeat depending on a few buying selling issues.

saki70 > take a look at those with built in amps for the bass units

blindjim > Thanks man. Got it. I’ve seen a few but have decided to go only partly in on low power high eff as a secondary system now.
It could change, though the odds say it won’t, but all of the jury isn’t back yet. So we’ll see. Mostly it looks like a PP amp.


Leotis > So I used the 4 ohm taps on my PrimaLuna HP Int to my "8 ohm" speakers
is there a simple explanation for the difference between the 4 ohm and the 8 ohm outputs?

Blindjim > Leotis, been there and done that myself.
When an amp has optional output taps, the amp is designed to output the total voltage and or current it produces into that load. Ie., 60wpc amp via 4 ohm tap = 60wpc. Same thing for the other taps provided the load or IMP of the speaker is similarly matched, unlike SS amps that automatically see or ‘feel’ the changes and react differently.
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Essentially, using a lower output tap or lower IMP on a higher IMP load or speaker will cut the power output by 50% or so. In any event it will be less power to the speakers if set up that way.

Speakers should be transparent enough to reveal upstream and room concerns, changes, and problems. For them to do their job as such, they need the right amount of power and the correct electrical operating environment, or as best is possible.

You can look at speakers like rocks. Look at an amp like a bulldozer or truck.

As strong as is a truck or bulldozer, it can only push a particular size of rock. Sure, it can easily push little rocks, or medium sized rocks, and even a larger 4 or 2 imnpedance sized rock but it has to match up to the rock as well with its gearing too, not merely its engine.

Using lower IMP taps sends less power to the speakers, IF the speaker IMP is much higher.

Highs will roll off, bass will be more bloomy, and usually the sound will be smoother and warmer because the speakers are being starved and can not fully demonstrate what they are capable of providing. Resolution will suffer, leading edges will get rounded off.

The sound will tend to be darker and more euphonic than normal as the speaker lacks the power to yield speed and fully demonstrate the entire bandwidth properly.

I did that mismatch with a couple different amps trying to get them matched up the best way possible. You don’t truly know what the imp curve is on many speakers, but amps do. They will tell you IF you pay attention and try the amps various taps..

Usually, the spkr maker gives you a really good indicator of what a nominal IMP for their spkrs run but that’s at one particular freq at one designated voltage. Like 1KHz at one watt, or 2.8 volts or so.

But what about power needs at other freqs? ImP will change then and music is made of many frequencies and volumes.

Its at times a best guess scenario so we use the amp to tell us what it likes, and we listen for the best match.

I liked the mismatched setting on a pair of speakrs I had as they were brand new and not fully run in. they sounded bright and thin on the right 8 ohm tap so I slid them onto the 4 ohm tap. Sounded much better then albeit a whole lot darker though.

after about three or four months I switched them onto the higher IMP tap and whoa! Night and day different! By then they were run in quite well. I begin getting loads of resolution, impact, better dynamics, more transparency, greater extension, every aspect of the reproduction improved. Thankfully they were 93db and an easy load of 6 – 8 ohms and I did not push them hard so the obvious lack of power did no harm to the tweeters. From clipping.

following the uptick to 8 ohm taps, and the greater resultant transparency ai was able to determine what did or did not work well in the system. Wha twas making things bright, rolled off, was buzzing, if there was a ground loop causing the trouble, more exactly how wires were contributing to the affair, etc., bedcause then I could hear things better.

Until then, I was like the system mostly in the dark. But for a while, it sounded OK to me. lol


Thank you for the very interesting answer!
Will have to study it a bit.
I did the swap using only 1 cut for a quick comparison.
What you say seems to correspond with what I heard.
Speakers are Revel F206. Even though nominally 8 ohm, the impedance curve looks mostly around 5 ohm or less.
http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1238:nrc-measu...
Will need to experiment a bit more.
I really appreciate your response.
Leo
@inna 

Ralph, would you like to tell us about disadvantages of OTL amp design? 0.5% distortion at full power is quite an achievement.
One thing is certain - more powerful SET amps done right are very expensive.
We get that figure without using feedback. With feedback the THD can be as low as 0.05% but we don't like feedback for the same reason that SET designers don't: it adds brightness.

OTLs have several disadvantages- speaker choice is an issue, as the smaller OTLs can't do 4 ohms very well. Generally speaking, if the speaker works with a low power SET it will work with a low power OTL too- the difference being that the 'low power' OTL will likely have several times the power of the low power SET.

The next issue is the number of power tubes, for example we use the 6AS7G which is good for about 10 watts. So you need a few of them if you want to make any power. Some OTLs use the EL509 or EL519, which are pentodes but the most common alternate is the 6C33. Four 6C33s will make about 60 watt in an OTL.

Finally, the smaller you make an OTL, the less efficient it becomes. So while our M-60 is perfectly comfortable on 8 ohm speakers, our S-30 is a lot more finicky about that- it can do well on some 8 ohm speakers but if there is a wild phase angle or the amp has to work hard it may not like it. Conversely, the bigger the OTL the more efficient it becomes so even though the class of operation has not changed, the bigger amps tend to have lower temperatures on each tube because more of the power is dissipated in the speaker rather than in the output section. 
leotis > Thank you for the very interesting answer!

Blindjim > No problem. I’d keep them on the higher taps for a while, listen, closely. That is of course once the amp has settled in on that portion of the circuit. A few days more or less should suffice. .

Another analogy for incorrect IMP matching of amps to spkrs could be like driving a 5 speed vehicle only in 2nd gear. It will take off and it will run but overall performance will suffer.

Another will likely be able to definitely say this more accurately, but I tend to think the taps on tformer output amps were designed to run in a range, not just one specific imp load. So I’m figuring the 8 ohm tap means about 8 ohms, and from above 4 to 8.
This is unless ther is a 6 ohm tap on the amp too. Then the range for the 8 tap diminishes to between 6 & 8 or above.
The 4 ohm tap is for that section of IMPs at or below 4 ohm loads.
Follow?

The only real worry is as said, clipping. Its when a driver is starved for power predominately. Usually it’s a tweeter. Ordinarily clipping occurs when running the spkrs at higher levels and the power a driver asks for can’t be provided appropriately or comes intermittedly. That’s when actual . damage to the loudspeaker can take place. It happened in a pr I had bought preowned. His INT did not have the power to satisfy those speaker’s demands and one of the four blew out. Quit working. The factory fixed it eventually. Once I paid for shipping and so forth.

Ralph, thank you, now I got it.  Yeah, relatively limited speakers choice. Number of tubes would not be a problem for me unless each cost $1k and lasted only for a year. It's a bit more difficult to do amp first approach than speakers first approach. But with Atma-Sphere and LAMM I would still do exactly that.