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Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!

63.194.80.83

Posted on April 15, 2000 at 14:38:09
Dave VH


 
Now that I've got your attention, I would really like to hear from anyone besides myself who has actually bothered to compare pure DH (directly heated) SETs and pentode SE amps. It bothers me that the "in-crowd" of SET fanatics will wax eloquently and in great detail about the sonic and musical qualities of their "pure" amps after extensive listening, but then put down pentode-in-triode mode amps without ever having heard them, even briefly. The same folks who berate Phlounder for making comments about equipment he has never heard are making strong negative comments about pentode-based SETs they have never heard. Technically, pentodes run in SET mode are indeed SETs, and should be given a fair chance to prove themselves.

Although I didn't have proper high-efficiency speakers with which to audition, I did compare a PP with an EL84 SET, and the EL84 SET with 300B SET last year. (I used my Apogee ribbon monitors, which have a flat impedance curve - unlike most ribbon speakers.)

I found the ASUSA EL84 SE kit amp to be very clean and revealing, and a good bargain at $500 with OEM tubes and signal path upgrades. The Cary/AE SE-1 with Valve Art 300B's was certainly stronger and more open with a more natural presentation of voice and acoustic instruments. I felt that both were much better than a Jolida SJ202 EL34 PP amp.

Doc B. has heard SUN SV-PM200 (a $780 kit which I have pictured above) integrated EL34 SE amp, and said that it sounded very good. (SUN also makes KT88 and 6V6 SE amps).

Tazsmonn is very happy with his SAS EL34 SE amps driving his Maggies, ad I don't think that ayone who puts down his gear has ever heard a SAS!!

Many inmates are happy with their 1-2watt ZEN SE amps.

So why are we seeing snootiness and one-upsmanship, even from people who haven't heard the amps that they are putting down? Wouldn't it be better to openly explore all avenues of single-ended amplification and compare qualities rather than limit this forum to de facto putdowns by single-minded fanatics?

The Asylum doesn't seem to be heading toward ban discussions of DEC/ZEN, SUN, ASUSA and SAS, but are folks, even moderators, trying to laugh them out of town? The "Purist DH SET" snootiness I have seen here lately is disgusting.

Dave van Harn

 

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    ...
*sigh*, posted on April 15, 2000 at 15:27:30
Jack G


 
I've heard a SE KT-88 amp, and it was "ok", but retained some kt-88ness. It was not as good as a 300B SET tho. I've heard a SE SS amp It was good, for what it was, but it wasn't as good as a SET. Imagine that. How unusual! I've also heard PP 300Bs and it wasn't as good as a SET 300b by the same manufacturer. How strange! I've heard several 2A3 SETs, that were better than 300B amps. OH MY GOD!!! SOME TUBES MAY ACTUALLY SOUND BETTER THAN OTHER TUBES! HOW BIZZARRE!!!!!!
So Dave, how many triode tubes have you listened to? At some point, one has to stop reading schematics, and listen.
Jack

 

What does "pentode in triode mode" mean, posted on April 15, 2000 at 15:47:03
Alex


 
As far I am concerned what matters is the singled ended circuit.
The "T" is not what matters to me as a conceptual matter, and furthermore I refuse to be a snob about 300B and 2A3. Having said that,
would someone please explain to me what "pentode in triode mode" means?! I've asked this question many times. Is it

1. really a SEP or
2. does one physically go into a pentode tube and "reconfigure" it?

I don't care much because I'm getting a "non-traditional" (sometimes described as bizarre) "T" but since I have thought of this (Zen amp)
and since you brought it up, I'll ask one more time what exactly does "pentode in triode mode" mean.

 

Jack, I'm not posting to start a "pissing contest"., posted on April 15, 2000 at 16:12:06
Dave VH


 
************************************
"And I hear they're making inflatable dolls more life-like now. I prefer the real thing. Jack"

What does your snide remark about inflatable dolls have to do with the musical tastes? What does your sex life have to do with musical preferences?

************************************
"You sound like someone depserately trying to defend their product. If yopu prefer the sound of trioded pentodes, thats your right. Just be aware, that others may prefer the real thing.
enjoy, Jack"

The only "real thing" is live music, and even that sounds different in different venues or seating positions. Your have your own taste, and others have theirs.
************************************

Please don't put down others or start challenging like Mtry when someone dares to question your authority. I have heard a fair number of amps and systems in my lifetime, but that doesn't make me a "guru." I have only heard a few SET's, and I really like them. However, even though you have heard more SET's than I have, I don't bow to your authority as the only right information about what constitutes "good" SET sound. I respect others as well, and I know that everyone doesn't agree with you.

What sounds "good" to you is not everyone's standard. I still strongly disagree with a forum moderator putting down others whose tastes are different from their own. You even felt compelled to attempt to belittle me down with your "schematics" remark.

Let's let people have their tastes and discuss them without putdowns and ego challenges. Otherwise, we might as well shut down the forum and publish a static "Jack's Gospel of SET's" since no on else's opinion seems to be valid.

Dave


 

A pure triode has three elements - cathode, grid and plate., posted on April 15, 2000 at 16:22:45
Dave VH


 
The filament is the cathode in a DH (directly heated) triode, while other designs use filaments as "heaters" that are separated from the cathode. In very simplistic terms, the cathode emits electrons which stream to the plate. The audio signal enters via the grid, which is between the cathode and the plate, and the high voltage from the plate takes the signal to the next stage, usually an output transformer for SE triode amps.

A pentode has two additional grids that are left unused when they are used in triode mode. Some people refer to this as a "pseudo-triode" mode.

See the article "How a Vacuum Tube Works" in the Asylum FAQ for more information on basic tube technology. It will clear up some of the basic concepts for you.

Dave van Harn

 

Re: Jack, I'm not posting to start a "pissing contest", but Dave has many good points here !, posted on April 15, 2000 at 16:41:24
What's next, Banisment for Unpopular tastes. I'll just go back to my writing of "The panel woofer from hell" for the MUG page. A high eff. woofer and crossover. I'm with you Dave, Bravo !

 

Chill, posted on April 15, 2000 at 17:58:31
Jack G


 
you didn't think i would react to your inflamatory post?

>>>The only "real thing" is live music, and even that sounds different in different venues or seating positions. <<<
true bbut since we dont have live music in our listening rooms, we have to settle for sudio equipement,hence AUDIOasylum

>>>Your have your own taste, and others have theirs. <<<
Isn't that what I said when i wrote:
***If yopu prefer the sound of trioded pentodes, thats your right. Just be aware, that others may prefer the real thing.***(meaning triodes)

>>>Please don't put down others or start challenging like Mtry when someone dares to question your authority<<<
WHAT ARE YOU TALKING ABOUT???
where did authority come in?I put no one down. the discussion was about triode wired pentode tubes Vs triode tubes. Why do you insist on mking a big deal out a little thing? There was no abuse involved.

>>>What sounds "good" to you is not everyone's standard. <<<
quite right-I'm sure there are people who think my system is horrible-so what?

you wrote this:
>>>The Asylum doesn't seem to be heading toward ban discussions of DEC/ZEN, SUN, ASUSA and SAS, but are folks, even moderators, trying to laugh them out of town? The "Purist DH SET" snootiness I have seen here lately is disgusting.<<<

clearly a shot at me. I responded with my schematics remark It was tit-for-tat, and I shouldn't have done it. It was wrong.
You seem to be overly sensative tho, and making a mountain out of a molehill about snootiness that is more imagined than real, for none was intended.
Do not let past incedences color your judgment.
Jack

 

Re: What does "pentode in triode mode" mean, posted on April 15, 2000 at 18:02:38
joe


 
It means the screen is essentially tied to the plate; thus you have a cathode, no.1 grid (signal input) and plate (and screen). The plate family of curves is exactly the same as a "pure triode". The distortions produced is exactly the same (except for different manufactures they vary slightly).

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 15, 2000 at 18:08:13
Interesting. Good subject.

The "best" sounding amps I've heard are "pure" SET -- a DHT output tube, all alone, feeding an OT driving a speaker. Ideally with choked, tubed rectification in power supply (though I'd wager that tubed rectification is not an absolute requisite with proper design and implementation).

The next best was the Cary 300B Stereo amp I lived with for a couple of years -- a push pull DHT amp with tube rectification. That was a very nice amp -- and had many qualities of the better SE direct heated triode amps we tend to obsess over. At the time it also had certain qualities (dynamics, bottom end speed and energy) that I had not yet heard in SET amps. It did not use an interstage transformer -- and the input driver was a 6SL7 if I remember correctly. This experience with the Cary 300B Stereo amp leads me to believe that there is tremendous potential in push pull direct heated triode amps -- and Sun (among others) has set a clear path that direction. Personally, I'm quite open to the posibility of an amp of this design eventually taking the place of my Wright 3.5 monoblocks. (If I could get the same "quality" sound with 15 wpc, I'd be interested! -- because my speakers are only 92db efficient. If I loved my speakers and they were 100db efficient, I can't imagine that it would matter.)

I've heard pentode tubes driven in triode mode -- both single ended and push pull. They sounded good -- but none of the amps in this category (that I have heard) had top quality power supply desings and implementations -- thus not a fair comparison. For example, I also found the ASUSA EL84 SE kit amp to be clean and revealing, but not very relaxed. It didn't draw me in.

I've not heard, ever, a SET amp, with parallel output tubes.

Keep talking.

WTS


 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 15, 2000 at 18:38:11
Joe


 
Maybe it is the money involved. After all, wouldn't you feel foolish if you spent a ton of money, only to realize you may have been taken?
And I think another point. You cannot judge anything, whether concepts or other, by reviewing just one or two companies products. Who says they have the ultimate design for any particular tube?

 

Re: A pure triode has three elements - cathode, grid and plate., posted on April 15, 2000 at 18:48:08
Joe


 
WRONG, WRONG, WRONG, WRONG. The screen and suppressor grids ARE connected to the plate. It is also possible to connect the suppressor to the cathode instead of the plate. The "triode connected tetrode/pentode" has exactly the same plate curves, transfer functions etc. as the "pure" triodes.
The harmonic structure is different from brand to brand, just as it is with the 300B and different brands.

 

Re: *sigh*, posted on April 15, 2000 at 18:53:51
joe


 
Scientifically speaking, you cannot make overall judgements from just one or two brands of amp. That particular brand couldn't make the KT88's sound pure. Others may. But it is impossible to audition all combination of amps., speakers, CD players together. The result is "from our experience" and define what the experience is. Otherwise, false impressions may be created.

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 15, 2000 at 18:57:15
joe


 
WRONG, WRONG, WRONG, WRONG. The screen and suppressor grids ARE connected to the plate. They are NOT left unused. The triode connected tetrode/ pentode" has exactly the same plate curves, transfer functions etc. as the "pure" triodes.
The harmonic structure is different from brand to brand, just as it is with the 300B and different
brands.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 15, 2000 at 19:01:17
TAZSMONN


 
I agree on the money bit Joe. In my case I felt I got a good deal and have used the money not spent on gear for lots of music.

Tazsmonn

 

?????, posted on April 15, 2000 at 19:17:22
Jack G


 
>>>Maybe it is the money involved. After all, wouldn't you feel foolish if you spent a ton of money, only to realize you may have been taken?<<<
What ton of money? One of the whole beauties of low powered SETs, is that they are or can be cheap. Wright's 2A3s are $1200/pair Moth is $1800. Sun's VT-25 is about $1K. Doc Bs are in the $1K range, and he'll be coming out with a 2A3 amp thats going to break records for inexpensive SETs. That arguments doen't fly any more.
enjoy,
jack

 

Re: ?????, posted on April 15, 2000 at 23:49:35
Joe


 
Well, I heard the Cary with 300B for $3500.00 and thought they were
totally crappy. Are these any better at the prices you listed? Maybe Cary just cannot design a good amp.

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 16, 2000 at 05:10:01
Well guys,
Can I butt in here? Of course, and thanks for the permission. Can I be a martinet and suggest that you are both kind of wrong? Joe gets close here when he says that "the suppressor may be connected to the cathode".
Well, aside from the EL34, I can't think of ANY Power Pentode/Beam Tetrode that doesn't have its suppressor grid permanently connected to the cathode. So I feel that other than the EL34, which I have not heard with the suppressor connected to the anode instead of the cathode, all beam/pentode power tubes are really still 4 element modified triodes. This may explain why they still seem to retain their "Pentode-ness" for lack of a better description. In fact, they still sound to my ears much as they do in Ultra-Linear or Tetrode modes. I hate to sound like I'm agreeing with Jack, but I kind of have to agree with him about the sound of tubes, period.
It would be interesting to float that suppressor in the EL34, and see if the sound breaks free from its "EL34edness". My own suspicion is that reliability might go "aus das fenster" if that suppressor has run with 400 or 500V parked on it. I hope I'm wrong. This would be an interesting experiment, and I'm sure that the tube's bias would be quite different as well...
Anyone out there try this already? I know I'd love to hear about it...

 

Re: *sigh*, posted on April 16, 2000 at 05:16:52
Well then let's it call it "statistical averaging", then. Some of us have heard ALOT of amps, and like an overused guitar riff, certain harmonic signatures keep popping up again & again. And the common theme is that we are listening to the same tubes, albeit often in vastly different amplifiers of vastly different topologies. To me, the KT88(Genalex) has a particular sound, no matter what I've heard it in. Ditto the 6550, the 8417, the 6BQ5, the EL34, the 7591, the 6B4, etc. ad nauseum. I design and build my own amps and can mess around with some very specific parameters. And I end up backing Jack's comments. Oh shock, oh horror.

 

Re: Chill, posted on April 16, 2000 at 05:20:37
Gee Jack,
I know I'm trying really hard not to let past incidents colour MY judgements...

 

Re: Jack, I'm not posting to start a "pissing contest", but Dave has many good points here !, posted on April 16, 2000 at 05:23:12
Banishment is not the only option for those of differing opinion & means of expressing it. There are other, sometimes even more curious forms of punishment to express one's disapproval, right Jackie Boy?

 

Re: ?????, posted on April 16, 2000 at 06:25:26
Jack G


 
I've owned the wright and the moth, and both are MUCH better IMO. I haven't heard the others, but I've been told they are very good too
Jack

 

My God, we agree! :-), posted on April 16, 2000 at 06:29:52
Jack G


 
That really was my point all along. Not matter what you do to a tube, it will, for the most part, keep its sonic signature. Now if one prefers a KT-88 or other pentode, thats fine. You just cannot make aKT-88 or 6550 sound like a 300B or 2a3 etc.
Jack

 

How about SEX amps? Paralell Single Ended., posted on April 16, 2000 at 09:10:59
Mike


 
These amps are PSE.

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 16, 2000 at 09:55:49
joe


 
Dear Joe,
Thanks for your input. Actually in KT88s and 6550s, the element is a beaming confining structure (plate looking) and not a wire/grid structure ( I am sure you knew this). There is no problem with the No.3 grid tied to the plate, as far as either dissapation problems or reliability from some other form. If the no.3 grid is connected to the cathode, the potential between this and the plate is great and reliability could suffer. The sonics of any particular tube type can
(as you know) be determined by the design of the circuit and physical design of the tube itself. Thus I am very careful to state categorically that one tube is better than another.

 

Re: How about SEX amps? *Parafeed* Single Ended., posted on April 16, 2000 at 09:59:33
Jack G


 
not parallel tubed.
Jack

 

clarification, posted on April 16, 2000 at 10:06:59
Jack G


 
Parafeed is a type of output transformer, and prrallel single ended is 2 (or more) tubes running in parrallel(as apposed to push-pull) per channel.
jack

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 16, 2000 at 10:21:08
Dave VH


 
My VERY limited knowledge is from building an ASUSA EL84 SE kit last year. The kit's schematic doesn't show the supressor screen strapped to the cathode, but does show the signal from the input/driver tube going to the control grid, the B+ connected to the screen grid and output transformer primary winding, and the plate connected to the other side of the output transformer. I see that in a typical 2A3 circuit like the Wellborne Moondog, the signal goes to the single grid of the triode, and that the output transformer primary windings have the high voltage B+ on one end, and the high voltage B+ on the other end.

Although I don't understand the details, I can now see that the implementation of the pentode in "triode" mode is not exactly parallel, at least in these examples.

Thanks for the feedback.

Dave van Harn

 

Thanks for the feedback and good discussion., posted on April 16, 2000 at 10:49:04
Dave VH


 
Lessons learned:

1. I obviously am still learning about audio circuits, and am still at a very elementary level.

2. Most people with extensive listening and design experience seem to agree that SE amps with "pure" triode tubes sound the best. (Which matches my limited experience.)

3. Even died-in-the-wool curmudgeons with different perspectives such as Joe Rosen and Jack G. can actually agree at times (the most pleasant surprise in this thread).

Other comments:

I still feel, however, that at this forum we should welcome and treat equally all SE amp fans, including those with EL84, EL34, KT88, etc. equally. When people who own or prefer "pure" SET amps make snide jokes about "inferior" designs and tubes, it doesn't always come across as a joke and can create an impression of snobbish and elitism.

I believe that two of the Asylum sponsors, Doc B's "Electronic Tonalities" and George Wright's "Wright Sound Company" provide the best budget-priced kit and ready-built SET amps, respectively, that are available on the market. But I also believe that the $400 ASUSA K2003 and Dec Zen SE amp kits with pentodes are great bargains for those on the smallest budgets.

I hope that all are aware that I started this thread to sort out the differences between ultra-purists and those with broader SE tastes in hopes that we can continue to forge a friendly forum where all single-ended amp fans can gather and enjoy their hobby.

Apologies to Jack G. if I seemed a bit too harsh in my initial criticism.

Dave van Harn

 

Re: clarification, posted on April 16, 2000 at 13:18:23
Mike


 
They ARE parallel Single Ended. And pretty good amps at that. Mike

 

Really? OK(nt), posted on April 16, 2000 at 14:00:20
Jack G


 
.

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 16, 2000 at 14:38:35
joe


 
Forgot to mention that beam output tubes almost always have beam plates connected to the cathodes internally, so you cannot change this. But obviously, obviously, if the suppressor grid (or if there is a beam power tube out there) is not connected to the cathode, it may be connected to the plate. Gotta cover all the bases or someone will correct you. Anyway, if the screen is connected to the plate, the plate family of curves and other curves will look like a triode. The majority of the plate current will flow to the plate though with a little to the screen. What protects the screen is that when the current is maximum, the screen/plate voltage is generally minimum. This of course is not necessarily the case in Radio frequency work. Especially as the R.F. frequency is increased. Then transit times and the simple distance difference between cathode and screen and plate make a difference. Many of the larger older type audio/RF tubes are only good to, say, 15 megacycles on up. It depends on the structure of the tube, internal lead dia., length, capacity etc.

 

Re: How about SEX amps? Paralell Single Ended., posted on April 16, 2000 at 16:20:03
The distinction I was intending was as Jack surmised...that there were two (or more) output tubes in a given channel, running parallel.
WTS

 

Re: ?????, posted on April 16, 2000 at 16:42:47
I lived with Cary 300B SE monoblocks for a couple of years before moving "down" to Wright 3.5 2a3 monoblocks (which are far superior amplifiers). My Carys were an earlier design, used the 6SL7 driver, and were probably manufactured in 1994 or 1995. They were very tube sensitive -- changing the output, driver, or rectifier tube had a substantial impact on the sound. They had a wonderful midrange magic that was not otherwise available at the time -- at least I had never heard a ss or a pp tube amp that came even close.

My strong impression is that Cary, more than any other manufacturer, popularized the niche market of single ended direct heated triode amps -- and for that we are almost all indebted. It was risky putting a $3,000 price tag on a pair of amps that measured 12 watts per channel when there were so few compatable speakers. Dennis H. designed and manufactured a "breakthrough" product (even if it's design was effectively 60 years old), convinced enough people to buy that a new market was created, made some good coin, and for his efforts we are all the richer.

I don't "know" if the newer Cary SE amps are better, I havn't heard them. I would presume that they have improved their designs, parts, and implementation -- market competition tends to be an effective motivator.

Context is important.

WTS


 

Re: ?????, posted on April 16, 2000 at 17:28:46
Jack G


 
I'm not sure how much they changed untill recently. I heard them a little later, and I *think* they were the same. The biggest difference, was the option of WE tubes, as apposed to the Cetrons. Yes, they had a good midrange. Now they are built arond the KR tubes and have more power.
Jack

 

Re: ?????, posted on April 16, 2000 at 17:50:47
Rod M


 
That's a funny story. Dennis was at Stereo Unlimited and told the story of his first CES. 100 watt PP amps for $2K and a 12 watt monster for $3K. Yup, everyone wanted the little, expensive one. So he reckoned, how about doing a 2 watter for $4K, great idea, less power, costs more. It was a funny story, but I suppose you had to be there while he nearly electrocuted his father with one of his first endeavors as a youth.

I agree, Cary was major factor in bringing SET into the main stream market.

 

Re: WRONG, WRONG, WRONG, WRONG, posted on April 16, 2000 at 23:17:24
They don't bother to show the suppressor connection on the ASUSA schematic presumably because it is inside the tube, and has no external connections or functions.
In response to Joe saying that the suppressor is more reliable connected to the plate than to the cathode in an EL34, it is interesting to note that this is virtually never the way you see it used. In fact, I cannot think of any amp that I've seen, homemade or production, that uses the suppressor connected to the anode/plate.

 

How about....., posted on April 17, 2000 at 06:27:40
Tom §.


 
....*real* triodes with indirectly heated cathodes (12B4, 6AS7, 6C33) compared to directly heated (2A3, 300B, 572, etc.)? I would be curious to hear opinions from people who have heard both kinds of tubes in SET topologies and could form an opinion as to whether or not the IHT tubes have a sound more similar to DHT tubes than triode-connected pentodes.

Tom §.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 08:26:27
Thorsten


 
Hi there,

First to say that I'll be adressing also a bit of the tailend of the whole previous, now archived discussion here.

All the time my MAIN argument was that compared on a level playing Field DHT's like the 300B are preferrable sonically to Triode connected Penthodes. And I feel the margin is not small.

That said, the design of the Amplifier has as much to do with the sound as the Valves used. I could think of a few 300B SE Amplifiers that make certain Ultralinear Push-Pull EL34 Amplifiers (like the Quicksilver) positively sound great.

So, only because an Amplifer has a DHT does not mean it's great and only because the output Device is a triode wired Penthode doesn't mean it's bad. This is not about the sound of a specific Amp but about how far we can stretch things.

Now to the criticism of my comparison. I feel first of all that it is not really valid.

If we observe the characteristic Data of an EL34 in Pseudo Triode Mode and a 300B, the Anode Impedances are quite close, as will be operating voltages and currents (try a EL34 at 350V and 60mA, it will sound quite decent). So identical Output Transformers can be used with no real sonic impact.

Secondly, valves where not "just plugged in", you cannot do that anyway. Sufficient care was taken on such items as the Cathode Bias resistors and the Heater Voltages, as well as an Increased +B for a similar operating point for the 300B despite the higher Bias Voltage. As said, an Output Transformer that works well for Triode Wired EL34's works well also for a 300B.

A Driver Circuit geared to driving PSE 300B's (in my case 6CG7; RC coupled to 5687; RC coupled to 300B or EL34) will actually have a much easier time driving the EL34 Grid with it's lower Capacitance and lower Gridleakage, so an EL34 Outputstage actually makes the Driver Circuit work less hard, so IF the sound is similar, the EL34 should sound better.

The outcome from this Experiment was quite conclusive. There is no comparison (on a level playing field) when EL34 (or indeed KT88 - they where tried too) is pitted against 300B. While it is perhaps not fair to extrapolate from the results of KT88 and EL34 to that of all triode wired penthodes, for the Question "Triode wired KT-88 or EL34 vs. 300B?" it is a quite conclusive answer.

I would also like to add that the EL34 equipped version is an exceptional Amplifier, which makes most of the Amplifiers I have had in my hands sound rather less than good. It's only that the 300B again is almost as much better....

So, I have no problems with people liking Amp's useing triode wired penthodes as output's.... I don't even have problems with people saying these are good amplifiers. No problem at all. I don't even have problems with people saying they like a specific Amp using triode wired penthodes better than a specific amp using DHT's.

I'm interrested only in pointing out that if you try to get the MAX out of a given Budget I feel that using 300B's over EL34 or KT88 as output Devices will at only a slightly higher cost go MUCH FURTHER, sonically speaking.

Later Thorsten

 

Re: How about....., posted on April 17, 2000 at 08:29:43
Thorsten


 
Hi Tom,

FWIW, I feel that a Triode Connected 813 (DHP) sounds very good and preferrable to the 6S33.... At the same time they are hardly comparable, as the 813 is essentially a Penthode version of the 845 and the 6S33 is more of 6AS7 on Steroids.

But I feel that the Direct vs. indirect heating mechanism is responsible here, rather than the "Triode vs. Penthode" Issue.

Later Thorsten

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 11:08:11
RussL


 
I have found this topic very interesting, particularly as I have had the pleasure of building both pentode and triode SE's. First I must declare at the outset I am not a fan of 300b based SE as I find them too euphonic to my ears. I am blessed with a very musical daughter who plays all manner of instruments (from piano to drums)both solo and in groups and I therefore have a first hand accurate reference available often in the annex to my house.I therefore am pursuing the impossible holy grail of trying to acquire an accurate nearly lifelike system.
Of the SE amps I've built each sounds better than the AR & Conrad J amps I previously owned. Although the EL84 pentode amp is very good I find that my 2A3 amp is far better all round. However I have recently completed a KT88 (triode mode) SE which sounds more accurate and musical.
I am now having a break from SE amps and am going to build an OTL to see if that comes any closer to my ideal.

 

Really., posted on April 17, 2000 at 11:26:29
Tom §.


 
The S.E.X. design used two 6DN7 tubes. The 6DN7 is classified as a dissimilar triode. What that means is that there was a low power (1 watt) and a high power triode (10 watt) in the same glass envelope. From what I remember from the published schematic, Doc paralleled the low power sections to drive the high power sections which were also connected in parallel.

I imagine that the ParaS.E.X. used the same circuit setup but used the parallel/shunt feed output stage technique instead of the conventional output.

Tom §.

 

Re: That's it!!!!, posted on April 17, 2000 at 11:41:41
Mike


 
Well said.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 17:05:56
I have been using a 6550 SET for many months while building my 300B amp. After all this talk I decided to mangle half my 6550 SET amp to take one of my ready and waiting Sovtek 300Bs and adjusted the bias accordingly. After one night of listening I was not that impressed. I will continue to listen and see if things get better but I can say that moving from 6550 PP ultra linear to 6550 SE triode was a MUCH MUCH more significant improvement than from the 6550 SE to the 300B SE. I do like the purple glow of the 300Bs though!

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 17:58:25
Oops forgot to mention the filament voltage was properly adjusted.
Also the 6550 was a cheapy A$25 no-name that came in unlabeled brown cardboard. These regularly develop (or are supplied with) cracks in the glass but seem to retain their vacuum ok.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 22:43:43
Steve


 
Great answer Dave. Thanks for the support.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 22:47:16
Steve


 
Good work Russell. At least you did some comparisons before you made a statement. That is more than I can say for some individuals I have heard about.

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 17, 2000 at 22:51:59
Steve


 
Thanks Thorsten. I like your comments and style. One thing, I hope you don't take badly, is that you didn't mention which KT88s you used, since as you know they do sound different. Just a comment here and thanks again for your experimenting.

 

All valves used in the test where russian ones.... (NT), posted on April 18, 2000 at 03:03:43
Thorsten


 
:-P

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 18, 2000 at 03:07:29
Thorsten


 
Hi there,

No offence meant, but having tested both Sovtek and Chinese 300B's against Svetlana 300B's I must say that the Sovteks came for me subjectively last (good bass though).... Than again, they are cheap so who cares.

Try a WE or Svetlana for a "big jump"....

Later T

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 18, 2000 at 05:29:14
RussL


 
I am using Tesla KT88's and find their midrange very good. this amp is still breaking in so won't comment yet on top and bottom end.

 

What is a troded pentode???, posted on April 18, 2000 at 06:25:45
Pär


 
What is a trioded pentode (or beamie for that matter)?
Should the signal be connected on g1 or g2 (or both)?
Should g2 be connected directly to A or via a smallish value resistor?
Should g3 be connected to A or K?
There are many ways to do it, and which counts as 'Triode', 'Pseudo' or 'Fake'?
What are we comparing? There are possibilites from " I troded my old radio set and it sounds rubbish" to Williamson with 807/KT66 in triode mode (signal g1, g2 to A via resistor, and g3 to K as "default").

 

Trioded. Not 'troded' (nt), posted on April 18, 2000 at 06:28:47
Pär


 
nt

 

Hearing an amp..., posted on April 18, 2000 at 08:07:47
Rich


 
in a single installation means absolutely nothing. I can make any amp sound crappy in the wrong installation.

 

Re: Hearing an amp..., posted on April 18, 2000 at 14:28:17
Jack G


 
So Rich, whatcha doin' about speakers?
Jack

 

Re: Pentodes (EL34, EL84, KT88, 6550, etc.) in SE triode mode suck!!, posted on April 18, 2000 at 18:41:47
As soon as one of the Sovtek dies, I will be buying Svetlanas

 

Re: Jack, I'm not posting to start a "pissing contest"., posted on April 29, 2000 at 15:17:11
joe


 
Dear Dave,
Thanks for your input. It is much appreciated. The messages I keep hearing is:
1)300Bs are sonically better. The question I have is does it sound like a live performance, or colored to meet someones taste.
2)The assumption here seems to be that each tube has sonic characteristics that cannot be changed. No one seems to mention that the distortion characteristics of "pseudo triodes" can be varied, and distortion products can be lessened, and do sound different, so I don't understand the comment that these tubes have a certain sonic character when that "character" can be changed? And if changed, then there is no one "character" of that tube.

 

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