favourite midrange,treble tubes

[Michael Koster]

I have a lot of respect for sbench but I can't believe that gain vs. signal level is a characteristic of the tube. As pointed out, the selection of load line and op point and the actual signal levels measured e.g. small or large signal (!) will have an influence on this. Was the harmonic distortion filtered out or left to influence the signal level reading? At the very least, the experimental setup needs to be disclosed so we can see what the heck was measured...

Cheers,

Michael

 

[jlsem]

DHTs are not the only microphonic tubes. But they are among the few that are extremely linear and have benign harmonic distortion. That sure helps in the mids and highs.

Oh, yeah. The most microphonic tubes I've ever experienced are the 417A and the 6H30. You didn't even have to tap them with a pencil to get them to do anything. You can sing into them like a, a... well, a microphone. DHTs are plenty enough linear and don't seem very microphonic under normal listening conditions.

John

 

[jlsem]

Some people like their food, and their music, highly flavoured so they add lots of things to it (salt, pepper, spices, SE distortion).

People may LIKE the sound of DHTs (and clearly many people do), but that does not mean they're linear, it means that people like the colorations.

Any data to suggest that people can distinguish between an amplifier with 1% distortion compared to one with .1%? Designing for vanishingly low distortion, low noise and things like channel to channel RIAA accuracy are nice academic exercises, but are there any published test results that support the validity of these ideas?

John

 

[DF96]

In the 1950's it was found that many people, but not all, preferred sound with a few percent of deliberately added second-harmonic distortion. I think they were given a knob to twiddle and asked to set it where it sounds "best". It was suggested at the time that this is because it adds harmony an octave up, so it sounds richer and warmer. I think I first saw this reported in a 1960's book by Moir. This finding seems to be unknown to, or denied by, people nowadays.

 

[Pano]

DHTs are plenty enough linear and don't seem very microphonic under normal listening conditions.

Yes, I agree. Something to be aware of, but not hard to deal with in practice.
SY is right about the small tubes. I have some small DHT triodes but have yet to use them, so can't really say how well they work, or not.

There is a lot of crying "coloration!" when there really isn't any. Since to 1920s the effect of harmonic masking has been documented. With the proper decay of harmonics, you just can't hear them - it sounds like a pure tone. That's how the ear works. Some DHTs are very good at this, some maybe not. Driver tubes don't seem to need to be directly heated to achieve the same transparency. I don't know why.

 

[JLH]

Oh, yeah. The most microphonic tubes I've ever experienced are the 417A and the 6H30.

If you think those two tubes are bad try the 6C45Pi. It is terrible! I have no idea how anybody can stand using that tube.

 

[jlsem]

In the 1950's it was found that many people, but not all, preferred sound with a few percent of deliberately added second-harmonic distortion. I think they were given a knob to twiddle and asked to set it where it sounds "best". It was suggested at the time that this is because it adds harmony an octave up, so it sounds richer and warmer. I think I first saw this reported in a 1960's book by Moir. This finding seems to be unknown to, or denied by, people nowadays.

Maybe so, but a few per cent is a long way from the less than 1% put out by most DHT amps at normal listening levels. Do you think you can hear the difference between 1% and .1% distortion in an amp, regardless of topology?

I don't think anyone is denying that so-called finding from the '50's, but it is really old hat and not relevant.

John

 

[Soonerorlater]

In the 1950's it was found that many people, but not all, preferred sound with a few percent of deliberately added second-harmonic distortion. I think they were given a knob to twiddle and asked to set it where it sounds "best". It was suggested at the time that this is because it adds harmony an octave up, so it sounds richer and warmer. I think I first saw this reported in a 1960's book by Moir. This finding seems to be unknown to, or denied by, people nowadays.

I remember reading in a HiFi magazine (HiFi Answers?) in the 70's how they asked a panel to rate two "different" amps hidden behind a screen. After they listened to it for a while it was then altered in some way as to introduce harmonics. The panel was then asked to rate the two amps and they all agreed they liked the "second" amp best.


Might be interesting to repeat the experiment - perhaps not with panellists who remember the 70's though!

 

[aardvarkash10]

so, lets see here.

I had assumed the o/p was looking at doing some rolling. The responses so far have wandered off into some reasonably esoteric regions of noodling and supposition and compare tubes that not only would require widely differing loads and power supplies through to wholesale changes in topology to compare.

Pretty hard to say at that point that the entire (or any) difference is down to the DUT. Microphonics notwithstanding.

 

[Pano]

Well I think the opening question was legit. But there just doesn't seem to be a good answer among this crew, so it's bound to wander a bit.

All I can say is that in my experience a well implemented DH-SET trumps all other topologies for naturalness and detail in the mids and highs. Really quite remarkable.

 

[pforeman]

Thanks everyone for your insightful dialog.

How's this for a rewording of the original question:

Of all the KT88,KT90,KT120,KT77,KT66 and all of their variants(EL34, E34L,
6L6GC etc.) Which tube do you like for smooth midrange and treble and imaging.
I really like the EH EL34, not sure if I should try other makers of EL34, or try something "completely" different.
Again a different amp is driving below 200Hz, so- mids on up.

Thanks
Paul

P.s. I have the medium outputs from edcore 15W GXSE's, and Edcore's
xpwr035 which puts out 200mA for the plates. so, not sure if I can drive the
KT120?

 

[andyjevans]

Why are you restricting yourself to indirectly heated tubes, then, if your goal is the best midrange and treble?

Bit like the old saying "Well, Sir, if I was going to London I wouldn't have started from here".

 

[piano3]

In the 1950's it was found that many people, but not all, preferred sound with a few percent of deliberately added second-harmonic distortion. I think they were given a knob to twiddle and asked to set it where it sounds "best". It was suggested at the time that this is because it adds harmony an octave up, so it sounds richer and warmer. I think I first saw this reported in a 1960's book by Moir. This finding seems to be unknown to, or denied by, people nowadays.

Talented children playing the piano nearly always(if they can reach) add octaves in the bass or even the treble without it ever being suggested to them.

 

[SY]

How's this for a rewording of the original question:

Of all the KT88,KT90,KT120,KT77,KT66 and all of their variants(EL34, E34L,
6L6GC etc.) Which tube do you like for smooth midrange and treble and imaging.

c) All of the above. Getting good audio performance is far more dependent on how you implement the output tubes than the particular tube choice among a set of good choices.

 

[pforeman]

nothing overly good, or bad to say about aforementioned tubes though?
I have a wide range of cathode resistor values to set my amp at, so that I can bias at many levels.
Sadly(?), my amp doesn't do DHT. Perhaps thats for the next amp I build.
Is it good logic to think about a KT90, or KT120 that I can bias "hotter" to achieve better sound than a regular KT88?
(Again not too interested in bass performance of the tube which is what I hear reviews talking about when they discuss KT88's and 6L6's)

 

[Vinylsavor]

Hi!

I don't know the circuit of your amp, if it is SE triode wired how about an unusual tube choice? I've built plenty SE amps with the 6CB5A in triode. Good for 7-8W. Excellent sound. Op point and triode curves quite similar to a 300B.
Very cheap at about $5 for NOS

But comes with a plate cap which some people don't like

Thomas

 

[SY]

nothing overly good, or bad to say about aforementioned tubes though?
...
(Again not too interested in bass performance of the tube which is what I hear reviews talking about when they discuss KT88's and 6L6's)

The ones on the list I've used (EL34, KT88, KT66, 6L6 variants) are all good tubes for push pull amplifiers. Design correctly with any of them and you'll get an excellent amp.

You need to read reviews by smarter people.

 

[Tubelab_com]

The thread starter stated he has a Simple SE. That restricts the choice of output tubes to those with a pinout the same at the 6L6 - EL34 - KT88 unless some board modifications are employed. I have made a lot of different tubes work in the Simple SE by hacking the board up a bit, including the 6CB5A. I don't remember anything special about the 6CB5A. It does rock in a P-P amp though. I got a bunch when AES put them on sale for $2 each a few years ago.

As with any tube amp setup, but especially a SE amp without feedback, the sound quality will be influenced the most by the synergy between the output tubes, OPT, and speakers. The choice of music, volume level, and personal taste are also big factors.

Of the tubes discussed so far I find myself using EH EL34's when listening for detail in the mids and highs. Getting a box full of them for $10 each might have biased my opinion though. The same box contained some EH KT88's. Those have much bigger bass, but do give up some mids/highs. I have tried several flavors of EL34's but the EH seems to work the best in my setup. I have tried several 6L6CG variants but find them somewhere in between the KT88 and the EL34. I remember liking the KT66's that I tried but haven't listened to them in a while. I havent tried KT77's KT90's or the KT120.

Another possibility is one of the super 6V6 variants made to withstand the high voltages found in guitar amps. I have a SSE that runs NOS 6V6GT's in triode mode. It sounds very nice but only makes about 2 watts per channel. This isn't enough for my Yamaha NS-10M's but high efficiency horns are under construction. The NOS 6V6 can not withstand the voltages found in most SSE's. I made a seperate amp using a lower voltage power transformer.

 

[Vinylsavor]

Hi tubelab,

I don't remember anything special about the 6CB5A. It does rock in a P-P amp though. I got a bunch when AES put them on sale for $2 each a few years ago.

It is worth to have a look at the 6CB5A again. I designed a range of amps around the 6CB5A which has been built by quite a few people. In triode mode the 6CB5A has nice linear plate curves. I tested them with a curve tracer. It can be used with similar operating conditions as a 300B. I'm running at at about 425V B+, 1 k cathode resistor, -70V grid bias, about 70mA. This is right at the max of it's ratings. It's taking this since years.

I'm using it with 3 - 3,5k OPTs, mainly Lundahl or Tango. Such amps have blown away quite a few 300B amps except for the most elaborate ones using old production WE 300Bs.

Sorry for going off topic. If there is interest I can open another thread, showing the schems and fotos of several 6CB5A amps


Thomas

 

[Pano]

Yes, please do!