pentode in triode mode SE vs a DHT SE like 2a3/300b

[tubelab.com]

Maybe one day I'll get both the el34 amp and the 300b amp working at the same time and then I'll know if its worth the bother.

I currently have an SE 300B amp, a P-P 300B amp, an SE45 amp, an SE 845 amp and a few SimpleSE's that can use 6L6GC's, EL34's or KT88's. I also have a SimpleSE using 6V6's. The DHT amps all use DC heaters. Most of the SimpleSE's have triode - UL switches and switchable cathode feedback.

Is one amp better than the rest? No. I tend to listen to an amp for a while, then change it for another. I have 3 amps (45SE, 845SE, and 300B P-P) set up for fast change over in my lab. There is definite differences in the character of each amp, some of these tend to make them more suitable for some types of music. The differences are not night and day on most music. If I want to play a female vocalist or some jazz, I will usually use the 45 amp it does the details the best. If I want it louder, I use the SE 300B amp, slightly more colored, a little less detail (Shuguang tubes). If I want to play rock, I will usually use one of the pentode amps in triode mode. These tend to do louder complex (many simultaneous sounds, lots of transients) music better. I only turn on the cathode feedback when there is heavy bass. When it is time to play loud rock or techno (Pink Floyd, Depeche Mode) then it is UL mode with the cathode feedbcak on with an Electro Harmonix KT88 biased up to nearly 40 watts of dissipation. This will shake the walls in ways that no SE DHT can, even the 845. The 6V6 in triode has a nice clear sound, but I don't find it DHT like. It doesn't have the power to rock though. The 300B push pull amp does the best with transients. It has the best bass too. Want to play Jimi or Metallica loud, I use this one.

Is this the definitive answer as to what amp you need? No, my musical tastes and my speakers may be far different from yours. I took some amps over to a friends house for a listen. He has 106db horn speakers with Lowther drivers. The TubelabSE with NX-483's (a 5 volt 45) in it sounded real nice and provided all the volume that you would ever need. When we hooked up the SimpleSE with 6L6GC's in UL mode the sound was horrible. This amp had just been used in my house with my small speakers, 86 db Yamaha's where it sounded good. We put in the EH KT88's and switched to triode mode. This sounded much better. We listened to it all afternoon. If I had these speakers, I would probably be building mostly low powered DHT amps, Some SE some P-P.

http://www.tubelab.com/Sound%20Checks.htm

I have dragged my amps to several other peoples houses and had many different experiences. I took one of my TubelabSE's to another house where the owner wanted to hear it in his bedroom for a second system. He already had a really nice looking 300B amp for his main system that he had purchased in Hong Kong. He wound up replacing that amp with my amp and after listening to 45's 2A3's and 300B's in it, he wanted the 2A3's. I was the least impressed with the sound of the 2A3's, but he thought that they were the best thing that he had ever heard. To each, their own. Only in this game finding your own can be expensive.

I do agree with one statement I read in this thread. For my tastes, the EL34 sounds the most like a DHT of all the common audio tubes. For some reason, I rarely use them though. But then I can just hook up a DHT amp.

I have come to another conclusion. The 300 B has a large "sweet spot" It will give good sound over a fairly wide range of operating conditions. Some triode wired pentodes have a narrower sweet spot. I think that the spot that I like may not be the spot that you like. The KT88 seems to be the worst in this regard. I like the sound of them just below the melting point (450 volts 100mA). The 300B seems easier to get right. I run them rather cold (350 volts) and anywhere from 70 to 90 ma sounds good to me. I run all of my SE amps with a higher load impedance that most people do, 5 to 6K ohms. This drops the distortion way down at the expense of some power output. This also improves the bass and transient response. I also think that the choice of output transformer is far more than the tube choice.

I have listened to a lot of tube amps. I have made a lot of tube amps, and will continue to make more. Sometimes, I make an amp, don't like it and take it apart the same day. I am still looking for the one amp that will do everything right. I haven't found it yet. I think that is the addicting thing about this hobby, there is always just one more amp around the corner. I have been dreaming of this monster SE OTL............ Maybe 10 or 12 6336A's, about a kilowatt of power input to make 20 watts per channel........It would only weigh about 100 pounds..........I have all of the parts........NOOOOOO! I have gathered the parts for this amp, and then talked myself out of building it at least three times. Where will it end?

[cotdt]

can the DHTs compete against the EL84 wired as a SET with no negative feedback? Mine just sounds too good, I wonder if there is anything better than the EL84. I am running them with lower voltage than the norm, since I'm using it as a headphone amp.

[jaymanaa]

My strapped EL34 amp (with no feedback) has pushed both 300Bs and 2A3s, out of duty in my main system. I'm not sure why it sounds better to me, but it does. I suspect the output iron has quite a bit to do with it. I agree with the higher load impedence theory as well, and am running 10k on the 34s at nearly 500v. Jay

[tubelab.com]

can the DHTs compete against the EL84 wired as a SET with no negative feedback?

The EL84 is one of those rare tubes that I have never used to build an amp. I have dozens around here, so someday it will happen. The 6V6 wired as SET without feedback comes real close to the 45 amp. The difference may be due to the Electra Print VS One Electron's as much as the 45 VS 6V6 SET though.

[schiller]

Originally posted by ray_moth
I already tried to answer this in another forum, but I'll throw it in here too for people to argue about:

The reason, possibly the ONLY reason, why those antiquated DHTs from eighty + years ago are still popular and still produced, is because they are amazingly linear. Just have a look at the plate curves for a 300B or 2A3 and compare them with those of a triode-strapped pentode or beam tetrode, and you'll see what I mean - the difference is quite dramatic.

Yes it is

Originally posted by ray_moth
I
The consequence of this is that a triode-strapped pentode/tetrode produces more odd-order harmonic distortion. A DHT has plenty of second-order and a much lower amount of third-order, and that's about it. A triode-strapped pentode/tetrode produces also 5th and 7th order distortion, which can make it sound harsher. ............

No it doesn't:

Some numbers, measured with the software spectrum Lab and
M-audio 192 sound card.
Signal is fed to the card through a OPA134 buffer,
with a frequency responce compensated voltage divider at the input.
Signal generator was Leader LAG-120A, AC voltage was measured with the HP ME260B/U.

Driver tube: 5687 choke loaded, 170v/12mA,
output tubes with about 80% max plate dissip, 2,5kOhm load- 6L6 with 5kOhm.

6A3 @ 3w/1kHz: -30db 2nd, -42db 3d

EL34 triode strapped @ 3w/1kHz: -25db 2nd, -58db 3d, -55 4th

KT88 triode strapped @ 3w/1kHz: -27db 2nd, -47db 3d

6L6 triode strapped @ 1w/1kHz (klipped with more than 1,2w :
-24db 2nd, -52db 3d

Driver distortion was about -50db 2nd at the above conditions.

As you see, total THD is much better with the 6A3 (about the half), but odd harmonics are higher. In fact, the triode was the only one where higher order harmonics (5th, 6th, 7th, 8th) were visible (end of scale is -80 db), but i didn't mention the numbers, because i have not checked the accuracy at these low levels.

Down to -50db, my measurments are very very close with these of a HP334 - total THD only of course -, which i had for a while at home.

This can be seen from the curves too: Not symmetrical curves (EL34) produce even order distorion.

Greetings
Konstantinos

[cotdt]

those distortion figures are horrible. my EL84 triode strapped, with no negative feedback, has 2nd order distortion at -55dB, and 3rd at -70dB. It is monotonically decreasing distortion, which is perfect.

[schiller]

Originally posted by cotdt
those distortion figures are horrible. my EL84 triode strapped, with no negative feedback, has 2nd order distortion at -55dB, and 3rd at -70dB. It is monotonically decreasing distortion, which is perfect.

They are not horrible, they are realistic. Just make a rough calculation with the curves. Your values are - if you allow me - very optimistic. At what level and with what kind of equipment did you measured them??

I'm sorry, but under 0,3% 2nd and 0,03% at full power with a stage - any stage - with no feedback is a joke.

By the way: almost every SE stage has monotonic decreasing distortion (exception: SE A2). Why is this perfect? Because Jean Hiraga (with all respect to him) says so, or are there any other reasons??

Best Regards
Konstantinos

[cotdt]

I use my SE EL84 with headphones, so I measured at my typical headphone levels (a few mW). Monotonically decreasing distortion is important because psychoacoustic research states that the human brain cancels distortion that is monotonically decreasing, because the human hearing organs add monotonic distortions to help pinpoint distance and location of the sound. So the brain has to compensate for it by cancelling out such distortions, but only if it is monotonically decreasing. That way, the sound is not harsh like how distortion is typically perceived, but is warm and tonally rich.

[arnoldc]

just like everybody else, we have our own preferences.

with what i've heard with EL84 thus far (vintage amps), i would say it is the pentode equivalent of the triode 300B. too much coloration for me. and to some, it is warm and full bodied

[cotdt]

Originally posted by arnoldc
just like everybody else, we have our own preferences.

with what i've heard with EL84 thus far (vintage amps), i would say it is the pentode equivalent of the triode 300B. too much coloration for me. and to some, it is warm and full bodied

Yes, that is how I would describe it as well. The EL84 SET is like 300B but without the hum. And you can apply negative feedback if you don't like the coloration, but to me it is the perfect way to color the sound. I like very much.