Hi,
Looking for opinions - power aside but all other things being equal, is there a noticeable difference between different types of output tubes. I am not thinking about different makes of the same tube but for example the KT88 compared with the EL34 - this comparison in particular interests me as I have a EL34 power amp and I am currently building a KT88. Apart form the difference in power, should I expect to notice any difference in the sound quality? I realise that this is a difficult question and will depend somewhat on the brand of tubes and of course the speakers - however, does anyone have an opinion?
Cheers,
Rob
Looking for opinions - power aside but all other things being equal, is there a noticeable difference between different types of output tubes. I am not thinking about different makes of the same tube but for example the KT88 compared with the EL34 - this comparison in particular interests me as I have a EL34 power amp and I am currently building a KT88. Apart form the difference in power, should I expect to notice any difference in the sound quality? I realise that this is a difficult question and will depend somewhat on the brand of tubes and of course the speakers - however, does anyone have an opinion?
Cheers,
Rob
Define "best", if you please. IMO, there is no best, in the absolute sense. After all, we're talking: whose room, whose ears, which speakers, what style of music, etc. ad infinitum.
There is a definite difference in the general voicing of true pentodes and beam tetrodes. The EL34 and the 6CA7 are electrically equivalent, but they don't sound the same.
There is a definite difference in the general voicing of true pentodes and beam tetrodes. The EL34 and the 6CA7 are electrically equivalent, but they don't sound the same.
Just to help keep things clear for me, can you verify the following?
6V6 - beam tetrode
6L6 - beam tetrode
EL84 - pentode
6BQ5 - beam tetrode?
6pi14pi - ?
EL34 - pentode
6CA7 - beam tetrode
6550 - I've seen this described as a "beam power pentode" - what the heck is that? I believe the 6550 is the evolution of the 6L6, which would suggest it is a beam tetrode.
KT88 - "kinkless tetrode" - so is this really a tetrode as the name implies, or is it a true pentode like the EL84 and EL34?
Can any generalizations be made, such as American tubes tend to be beam tetrodes and the European tubes are usually pentodes?
Which do you tend to prefer, beam tetrodes or pentodes?
Do you find any truth in this quote?
"Pentodes have a poorer damping factor compared to Tetrodes in similar circuits, which means we can get more output tube distortion. Of course, with a bit of feedback in the amplifier, we'd be hard pressed to differentiate between the two sonically, but the fact remains that the pentode output stage is run without any negative feedback, making clean headroom take a back seat. The only 'drawback' to a real Pentode versus a Beam Power Tetrode is the sad fact that Pentode tubes are more susceptible to a potentially damaging Screen current rise at maximum signal than Power Tetrodes. This is because the beam forming plates in a Beam Power Tetrode drastically cut down on secondary emission, which will help keep the Screen Grid current increase at full throttle to a minimum. "
http://www.tone-lizard.com/Vox_Myths.htm
6V6 - beam tetrode
6L6 - beam tetrode
EL84 - pentode
6BQ5 - beam tetrode?
6pi14pi - ?
EL34 - pentode
6CA7 - beam tetrode
6550 - I've seen this described as a "beam power pentode" - what the heck is that? I believe the 6550 is the evolution of the 6L6, which would suggest it is a beam tetrode.
KT88 - "kinkless tetrode" - so is this really a tetrode as the name implies, or is it a true pentode like the EL84 and EL34?
Can any generalizations be made, such as American tubes tend to be beam tetrodes and the European tubes are usually pentodes?
Which do you tend to prefer, beam tetrodes or pentodes?
Do you find any truth in this quote?
"Pentodes have a poorer damping factor compared to Tetrodes in similar circuits, which means we can get more output tube distortion. Of course, with a bit of feedback in the amplifier, we'd be hard pressed to differentiate between the two sonically, but the fact remains that the pentode output stage is run without any negative feedback, making clean headroom take a back seat. The only 'drawback' to a real Pentode versus a Beam Power Tetrode is the sad fact that Pentode tubes are more susceptible to a potentially damaging Screen current rise at maximum signal than Power Tetrodes. This is because the beam forming plates in a Beam Power Tetrode drastically cut down on secondary emission, which will help keep the Screen Grid current increase at full throttle to a minimum. "
http://www.tone-lizard.com/Vox_Myths.htm
I would have thought that this question would have brought forth many more "expert opinions" by now. As previously stated there is really no "best tube". The "best tube" for one particular amp, may sound so - so in another amp, or in the same amp under different conditions, or even in the same amp under similar conditions with different music.
This brings me to my opinion. I have a SimpleSE set up so that I can run EL34's, KT88's or 6L6GC's without changing anything. I find that EL34's reveal more of the details in the music than the other tubes, and the KT88's have more bass and flat out rock better than the others. So if you want to play Metallica turned up to 11, use the KT88's, if you want to hear the details in Norah's voice, use the EL34's. 6L6GC's fall somewhere in between.
I have not tested any of the high dollar tubes (not in my budget). My favorite EL34's are JJ's and the KT88's are Electro Harmonix. I tend to swap between these tube sets depending on my musical preferences at the time, and how loud I am going to crank the volume.
This brings me to my opinion. I have a SimpleSE set up so that I can run EL34's, KT88's or 6L6GC's without changing anything. I find that EL34's reveal more of the details in the music than the other tubes, and the KT88's have more bass and flat out rock better than the others. So if you want to play Metallica turned up to 11, use the KT88's, if you want to hear the details in Norah's voice, use the EL34's. 6L6GC's fall somewhere in between.
I have not tested any of the high dollar tubes (not in my budget). My favorite EL34's are JJ's and the KT88's are Electro Harmonix. I tend to swap between these tube sets depending on my musical preferences at the time, and how loud I am going to crank the volume.
6V6, 6L6, are indeed beam tetrodes. As are the original KT88 and 6550. I have never seen any of these tubes that were not beam tetrodes.
The original 6BQ5's and EL84's were true pentodes. It is possible that some newer tubes could have beam tetrodes, but all of the ones that I have seen are pentodes.
The original EL34's and 6CA7's were true pentodes, although I have seen both type numbers on some beam tetrodes.
As for generalizations, as the vacuum tube era waned and production ramped down, many manufacturers all over the world started stuffing all sorts of unusual combinations into the glass.
The statement that pentodes may be more succeptable to screen current overload may have some basis. This should not make much difference in a HiFi application since the amp should not spend too much time in the overload region. The story is different is a guitar amp cranked to eleven. Some tubes got poor reputations from the guitar amp industry. Some manufacturers built tubes specifically for the guitar amp industry. The Sylvania 6L6GC STR was one of these. The EL34 was heavilly used in guitar amps, and the beam tetrode versions were probably made for survival in guitar amps. Most of the ones that I have seen were Japanese.
The original 6BQ5's and EL84's were true pentodes. It is possible that some newer tubes could have beam tetrodes, but all of the ones that I have seen are pentodes.
The original EL34's and 6CA7's were true pentodes, although I have seen both type numbers on some beam tetrodes.
As for generalizations, as the vacuum tube era waned and production ramped down, many manufacturers all over the world started stuffing all sorts of unusual combinations into the glass.
The statement that pentodes may be more succeptable to screen current overload may have some basis. This should not make much difference in a HiFi application since the amp should not spend too much time in the overload region. The story is different is a guitar amp cranked to eleven. Some tubes got poor reputations from the guitar amp industry. Some manufacturers built tubes specifically for the guitar amp industry. The Sylvania 6L6GC STR was one of these. The EL34 was heavilly used in guitar amps, and the beam tetrode versions were probably made for survival in guitar amps. Most of the ones that I have seen were Japanese.
A few more differences I'm aware of, between pentodes and beam tetrodes:
* BTs have a sharper 'knee' in the pate characteristic curve.
* BTs often do well in Class AB2 (grid current), e.g. 807 and 6146, but I'm not aware of any pentodes that do.
* BTs need much lower grid 'leak' resistors than pentodes for bias stability.
* BTs are reputedly more prone to parasitic oscillations.
* BTs, in general, take lower screen current than pentodes, as a percentage of plate current.
With all the differences between the two, it seems very likely that they should sound different. As to which sounds better, well, that's a matter of personal opinion I guess. I don't think there's anything fundamentally wrong with either design that would cause it to sound inferior, provided it's used properly.
* BTs have a sharper 'knee' in the pate characteristic curve.
* BTs often do well in Class AB2 (grid current), e.g. 807 and 6146, but I'm not aware of any pentodes that do.
* BTs need much lower grid 'leak' resistors than pentodes for bias stability.
* BTs are reputedly more prone to parasitic oscillations.
* BTs, in general, take lower screen current than pentodes, as a percentage of plate current.
With all the differences between the two, it seems very likely that they should sound different. As to which sounds better, well, that's a matter of personal opinion I guess. I don't think there's anything fundamentally wrong with either design that would cause it to sound inferior, provided it's used properly.
Putting a KT88 into a circuit fit for EL34's can often sound dull at the top end and the square wave will show it and also the otherway round.. It depends on what circuit and output config you are using. Although many IO tubes are interchangable, there will be bias and load Z differences which (the latter) will effect the sound.
The most influencial I find is between a 6550 and EL34. The 6550 is a lower running Z tube and with a well matched o/p tranny can provide stunning performance but look at the bias requirements ?. So said for others.
I like EL34's, all makes behave well. Personally I would abandon the KT77 and use KT88's instead.
This reminds me about the 6L6. Data sheets quote B+ max at 360V. Who's using them higher than this and in what mode. I came across one design at 450V+ true p-p ?? That's pushing it.
rjich
The most influencial I find is between a 6550 and EL34. The 6550 is a lower running Z tube and with a well matched o/p tranny can provide stunning performance but look at the bias requirements ?. So said for others.
I like EL34's, all makes behave well. Personally I would abandon the KT77 and use KT88's instead.
This reminds me about the 6L6. Data sheets quote B+ max at 360V. Who's using them higher than this and in what mode. I came across one design at 450V+ true p-p ?? That's pushing it.
rjich
Ty_Bower said:
It's a difference in terminology. Real tetrodes, those with a cathode, control grid, screen grid, and plate disappeared early on. Real tetrodes have a nasty negative resistance "kink" in the plate characteristic that must be avoided (unless you're making UHF oscillators). Pentodes were originated to eliminate that negative resistance characteristic.
The "beam" tubes were developed to beat a patent, and so the developers avoided the word "pentode" deliberately, referring to it as a "kinkless tetrode" to avoid legal problems. However, "pentode" simply means "five electrodes", and that's how many beam tubes have: 1) cathode 2) control grid 3) screen grid 4) beam formers 5) plate. Therefore, it is a pentode. Once the pentode patent lapsed, they became to be called "beam pentodes".
Don't know; don't care. I'm not one of those audiophools who thinks that gNFB is the spawn of the devil. Using local and/or global NFB can improve the damping factor of any amp that uses pentode finals. So far, I've done designs with the 807 and the 6BQ6 (both BPPs) run as pentodes, and the included gNFB keeps the speeks under control as well as eliminating that pentode nastiness. Both sound just great.
Rob11966 said:
I like the KT88 better than the EL34 in circuits good for each one. The EL34 is moodier and the KT88 is cleaner and gutsier. I like EL34 more in UL with 15-20dB feedback than in Triode with less than 12dB feedback. I like EL84 better than 6V6 for lighter program and 6V6 better for Symphonic and Rock. I like 2A3 better than 300B. I like push pull DHTs better than SE DHTs, when driven properly.
By the way, Diode, Triode, Tetrode, Pentode are Greek words and mean 2way,3way,4way,5way.
Which tube is better
From my opinion, I can say: none of them, and all of them. Why? It depends on what circuit, what type of OPT., Caps., resistors, and couplings to be used.
The main factor is your ears!, One men's meat is another's poison. whenever you like, may the other's don't. Before you build a circuit, you have to understand the characteristic of each component. pentode, tetrode, triode or beam tube have their own characteristic, utilize correctly will achieve best performance, consult more experts will give you more valuable ideas. The choice of tubes is your opportunity. other person's idea just take it for reference!
From my opinion, I can say: none of them, and all of them. Why? It depends on what circuit, what type of OPT., Caps., resistors, and couplings to be used.
The main factor is your ears!, One men's meat is another's poison. whenever you like, may the other's don't. Before you build a circuit, you have to understand the characteristic of each component. pentode, tetrode, triode or beam tube have their own characteristic, utilize correctly will achieve best performance, consult more experts will give you more valuable ideas. The choice of tubes is your opportunity. other person's idea just take it for reference!
richwalters said:
Have you seen a cct. uses 420V to drive a PP EL84, that is. Sansui AU70, and Dynaco ST-35. From data sheet, EL84 max plate voltage is 380V dc., but if you float up the cathode voltage to 40V. ( that is the neg. bias of the tube required ) therefore, actually is 420 - 40V, the tube is working on 380V. that is the trick???
And also there is a tolerance +/- designed by the tube manufacturer, in such case, the tube can work at the upper limit side of it's parameter.
As long as you drive the tube below it's plate dissipation, the tube still can work fine without any damage. When the Voltage exceeded the max. rating, lower the plate current so that push the tube back to the safe side just by increase the neg. bias.
I have built a SE 6V6 amp. using 340V plate voltage, but I set the quesent current to 30ma. with fixed bias, this gives me clean and fast sound.
An externally hosted image should be here but it was not working when we last tested it.
Just kidding. I like EL84-types and my KT77's, but 6L6GC's have a nice sound. I think your speaker types and music styles will have more of an impact on sound than the types of tubes themselves..
Hi Eli,
I guess I asked the question without thinking too much about the definition of 'best' and the possible answers to the question. You are absolutely correct, perception of sound is very subjective and I guess that I really can't define best. Personally I know what I like but I can't claim that this is the best!
Perhaps a better way of asking the question would be how do these tubes compare in sound quality, all else being equal (which it rarely is)? or even a simple poll - What tube do you prefer the EL34 or KT88?
Interesting comments so far.
Cheers,
Rob
I guess I asked the question without thinking too much about the definition of 'best' and the possible answers to the question. You are absolutely correct, perception of sound is very subjective and I guess that I really can't define best. Personally I know what I like but I can't claim that this is the best!
Perhaps a better way of asking the question would be how do these tubes compare in sound quality, all else being equal (which it rarely is)? or even a simple poll - What tube do you prefer the EL34 or KT88?
Interesting comments so far.
Cheers,
Rob
From V52.com we have the following:
OUTPUT TUBES
1 RS241 Telefunken Great warmth in mids, detail in highs. Great tube all-round!
2 UX-210 RCA/Cunningham Great on voices and highs, gives off light!!! A winner.
3 UX-245 RCA/Cunningham Nice tube, round/warm sound, detailed, very musical.
4 VT-52 Hytron Great detail in mids, a little coarse in highs, good bass.
5 45 (ST) RCA A bit lacking in sweetness, otherwise very musical and lively sound.
6 UX-171A RCA/Cunningham Excellent all-rounder, highs a bit less articulated, very nice mids.
7
8 31 RCA Very clear and detailed, a bit dry in the mids/lows.
9 275A Western Electric Good mids/bass, weaker in highs.
10 300B Western Electric Middle of the road. Warm bass, fuzzy warm mids, laid back highs.
Most of these are low power and we should chuck in the 2a3 and 845 for sure. In practical terms, I'd suggest 2a3 for lower power and 300b for higher power. 845 is high volts if you like that kind of thing.
OUTPUT TUBES
1 RS241 Telefunken Great warmth in mids, detail in highs. Great tube all-round!
2 UX-210 RCA/Cunningham Great on voices and highs, gives off light!!! A winner.
3 UX-245 RCA/Cunningham Nice tube, round/warm sound, detailed, very musical.
4 VT-52 Hytron Great detail in mids, a little coarse in highs, good bass.
5 45 (ST) RCA A bit lacking in sweetness, otherwise very musical and lively sound.
6 UX-171A RCA/Cunningham Excellent all-rounder, highs a bit less articulated, very nice mids.
7
8 31 RCA Very clear and detailed, a bit dry in the mids/lows.
9 275A Western Electric Good mids/bass, weaker in highs.
10 300B Western Electric Middle of the road. Warm bass, fuzzy warm mids, laid back highs.
Most of these are low power and we should chuck in the 2a3 and 845 for sure. In practical terms, I'd suggest 2a3 for lower power and 300b for higher power. 845 is high volts if you like that kind of thing.
Hi,
for best sounding output tubes I´d rather look at triodes not tetrodes, pentodes or xxodes.
And among these the new highly linear designs of KR-Audio range in the top group.
See KR300BXLS, T100, T1610, KR845.
Designed with Audio in mind.
But apart from this, the circuit design and the complete surroundings are probabely of greater influence
Calvin
for best sounding output tubes I´d rather look at triodes not tetrodes, pentodes or xxodes.
And among these the new highly linear designs of KR-Audio range in the top group.
See KR300BXLS, T100, T1610, KR845.
Designed with Audio in mind.
But apart from this, the circuit design and the complete surroundings are probabely of greater influence
Calvin
Forgot to mention the 6B4G which is handy if you have octal sockets already installed. There again, you don't have to use the big oval ceramic UX4 sockets for 300b and 2a3, because with a bit of searching on ebay you can find octal size ones that can swap into the same sockets. As the poster above says, if you want anyhthing like the best think triode. I'd add, think directly heated triode.