I cannot answer your questions directly as I have not tried that. However, having gone the tube way, I would not go back to solid state. This is quite ironical, as I went from tube ( my first home made amp 30 years ago ) to solid state because of better freq response, and now back to tubes again. I do not know if age was the cause of my change in taste ( when you are young you will prefer boom boxes ).
The stock Ella was clinical, warm sound, good imaging and absolutely no character. I would say very good. BUT, it's true potential can be unlock with simples mods that are easy to do. Thats the fun part. You can color the sonically neutral sound to anything you like and to hell with what others think. Tailor your own joy!
I just received my big bottles, the 6550s. Will be trying them out soon after breaking them in for a day. I do not think it would be as smooth as the EL34s but sometimes I want a bit more power than the EL34 can ooze out.......
My joy is not in music but the journey in making the music I want, when I want, and the learning ( and burning my fingers, electrocuting them as well etc etc )
The stock Ella was clinical, warm sound, good imaging and absolutely no character. I would say very good. BUT, it's true potential can be unlock with simples mods that are easy to do. Thats the fun part. You can color the sonically neutral sound to anything you like and to hell with what others think.
Tailor your own joy!I just received my big bottles, the 6550s. Will be trying them out soon after breaking them in for a day. I do not think it would be as smooth as the EL34s but sometimes I want a bit more power than the EL34 can ooze out.......
My joy is not in music but the journey in making the music I want, when I want, and the learning ( and burning my fingers, electrocuting them as well etc etc )
Interesting impressions on the 6550 in this amp. I haven't tried them or kt88s.
What El34 are you using? I think the EH version is wonderful. I was using them for a long time in triode mode at pretty high idle current.
You may have missed my re: on the diyhifi board. When you bypass the 6922 cathode resistor you are removing loop feedback from the amp. So if you find the bass boomy you may want to put the feedback back to gain some damping on the output. I don't see a 22uF cap anywhere in the stock circuit. Maybe you could explain this mod.
fwiw, I drive the amp directly from a cdp w/ shunt attenuation on the amps input and would not have it any other way. (well maybe a tranny attenuator would be better)
-zarni
What El34 are you using? I think the EH version is wonderful. I was using them for a long time in triode mode at pretty high idle current.
You may have missed my re: on the diyhifi board. When you bypass the 6922 cathode resistor you are removing loop feedback from the amp. So if you find the bass boomy you may want to put the feedback back to gain some damping on the output. I don't see a 22uF cap anywhere in the stock circuit. Maybe you could explain this mod.
fwiw, I drive the amp directly from a cdp w/ shunt attenuation on the amps input and would not have it any other way. (well maybe a tranny attenuator would be better)
-zarni
hang on positron, What's about the KT88 that requires vast experience....?????? Can you expand ?
okay we know about the high gm and parasitic oscillation which can effect both tubes and any output trannny design.....
No....The EL34 isn't my favorite tube and only deserves bench testing repairs. It isn't a pokey tube. Use a KT88/6550 in an EL34 circuit and is poss to adjust nearly for class A with much better performance, that is if the power supply is up to it.. Hint... the GEC 30Watt design does a comparison between 66's and 88's. You can use a KT66 in an EL34 circuit with nearly no changes and an 88 for slightly more power with lower HT.
I agree I am one of those who is using SS preamps and tube main amps.
rich
okay we know about the high gm and parasitic oscillation which can effect both tubes and any output trannny design.....
No....The EL34 isn't my favorite tube and only deserves bench testing repairs. It isn't a pokey tube. Use a KT88/6550 in an EL34 circuit and is poss to adjust nearly for class A with much better performance, that is if the power supply is up to it.. Hint... the GEC 30Watt design does a comparison between 66's and 88's. You can use a KT66 in an EL34 circuit with nearly no changes and an 88 for slightly more power with lower HT.
I agree I am one of those who is using SS preamps and tube main amps.
rich
KT88s
I mention vast experience since so many seem to be down on the tube. I would obviously be using a different tube if I thought others would be better.
I, of course, won't give out my designs, and other schematics I have on hand don't do the tube justice.
Parts selection is critical too, but no one wants to test for the most neutral sounding parts. Most seem to sonically adapt the parts to a particular tube rather than the other way around.
So it is probably better for most people to use a different tube.
What I am hoping to accomplish is to get people interested in testing parts for sonic neutrality. That way, they can improve their designs, sonically, which I think people want.
I don't wish to imply that no tweeking is necessary, but, hopefully, tweeking will be lessened and fidelity improved.
Don't mean to offend anyone.
I mention vast experience since so many seem to be down on the tube. I would obviously be using a different tube if I thought others would be better.
I, of course, won't give out my designs, and other schematics I have on hand don't do the tube justice.
Parts selection is critical too, but no one wants to test for the most neutral sounding parts. Most seem to sonically adapt the parts to a particular tube rather than the other way around.
So it is probably better for most people to use a different tube.
What I am hoping to accomplish is to get people interested in testing parts for sonic neutrality. That way, they can improve their designs, sonically, which I think people want.
I don't wish to imply that no tweeking is necessary, but, hopefully, tweeking will be lessened and fidelity improved.
Don't mean to offend anyone.
Yes, but
I know what you are saying Fd, and you are probably doing more than most in this regard. You kinda remind me of Thomas Edison, always experimenting and trying new things. I have spent years testing and finding the most natural sounding parts possible.
All the schematics I have on hand are not very good using the KT88. I cannot, for good conscience, recommend them to those who wish to try the tube. A different approach seems necessary in order to get great sound from the tube.
That is about all I can say without giving too much info out.
I know what you are saying Fd, and you are probably doing more than most in this regard. You kinda remind me of Thomas Edison, always experimenting and trying new things. I have spent years testing and finding the most natural sounding parts possible.
All the schematics I have on hand are not very good using the KT88. I cannot, for good conscience, recommend them to those who wish to try the tube. A different approach seems necessary in order to get great sound from the tube.
That is about all I can say without giving too much info out.
Complement
Believe me FD, it was a complement I was giving you.
When one uses the best/neutral sounding parts and designs, my KT88 designs produces natural inner detail, not artificial, which does sound different, and is at least as good or better in every catagory, including midrange detail, than the DHT amps I have heard. It is much more "live" and natural sounding.
Believe me FD, it was a complement I was giving you.
When one uses the best/neutral sounding parts and designs, my KT88 designs produces natural inner detail, not artificial, which does sound different, and is at least as good or better in every catagory, including midrange detail, than the DHT amps I have heard. It is much more "live" and natural sounding.
Dementing KT88's
Interesting commentary on the KT88’s. I’m suprised to it’s low standing. Revenge for my opinions of the EL34 ?????
Having been in audio for some time, the KT88 was origonally a top flight tube British (CV5220) and will only perform it’s best when used with a slam low impedance driver stage.... Technically looking at the spec figures (can be used up to 800V B+ max) compared with 500-600V for 6550 series; the 88 has a lower reverse g1 current (which indicates vacuum state). However most of us don’t use them in that high voltage. I’ve seen it used in commercial amp designs at 600V @ 65mA quies, pretty well in red heat; beyond 6550 working zones. Is it overdesigned for audio use ?? It was des.miitary tube, as were most others. It is the highest rated Int Oct tube in it’s class which offers the lowest distortion versus poke. Anyone “better” that ??? So why the problem with audio. Okay use it without an A-G2 snubber and it’s liable to take off and behave an RF transmitter. The best SS designs are immune to this either. I use the KT88 up to 100Khz without snags, perhaps that’s down to how I use it. Skill ? perhaps positron you are right.......I’ve got so used to it.
I’m convinced that most of these “differing views” regarding output tubes (even mine scathing the EL34) should really be more directed to some miserably configured intermediate stages for creating the poor sound and lousy harmonics. Especially when the long tailed configuration is power drive and quenching Miller effect, effectively trying to do two jobs in one. I’m abs’ against this horror configuration unless followed by a non-loading driver stage....this may be the secret of best designs.
Sine wave tests on the Mullard 20Watt exposes a poor looking Lissajous pattern at 10Khz or in laymans’ terms the phase change is goes to pot contributing to THD. It’s not the phase change in the o/p transformer always to blame..... but unsymmetrical quenching of o/p tube Miller effect misbalancing the driver tubes creating a “phase hang-over” at HF leading to high THD.
Apply Miller effect theory (as used in Mosfet drive calculations) and then the impedance cum driver picture becomes clearer of what the drivers have to do. My version of Spice doesn’t uncover this pecularity.
This particular long-tailed pair design uses uses 180K resistors in the ECC83 phase splitter to effectively drive the EL34’s but have a look at the auto bias dampers 470K each....... an amp with overall high loop gain and 30dB feedback @1Khz.. The HF response is high but at very high THD creating a muddled sound.. Interestingly I’ve heard users replacing the EL34’s with KT66’s or even older 6CA7’s have obtained a “better imaged sound”. There is more to all of thisl.
I don’t want to daunt anyone wanting to make this design up as it’s an easy tame P-P starter amp and it will deliver the goods. The S/N is also very good at nearly –90dB below 20W but I don’t rate it at top end Hi Fi quality.
So back to the user of parallel EL34’s in multiple push-pull, it depends whether fixed bias or auto is used and use a good driver stage. One can use cathode followers for drive ease or a well designed high current driver a design sim to Williamson used, except with much lower resistor values.
It isn’t suprising that most of the push pull amp designs that use interstage drivers with a common cathode configuration (excellent C.M rejection) seem to be the best sounding performers.....Williamson etc....GEC88-50..so become not so dependant on the O/P tubes. The same drive comments goes for SE designs.
Comments welcome
Viva KT88’s 807’s
rich
Interesting commentary on the KT88’s. I’m suprised to it’s low standing. Revenge for my opinions of the EL34 ?????
Having been in audio for some time, the KT88 was origonally a top flight tube British (CV5220) and will only perform it’s best when used with a slam low impedance driver stage.... Technically looking at the spec figures (can be used up to 800V B+ max) compared with 500-600V for 6550 series; the 88 has a lower reverse g1 current (which indicates vacuum state). However most of us don’t use them in that high voltage. I’ve seen it used in commercial amp designs at 600V @ 65mA quies, pretty well in red heat; beyond 6550 working zones. Is it overdesigned for audio use ?? It was des.miitary tube, as were most others. It is the highest rated Int Oct tube in it’s class which offers the lowest distortion versus poke. Anyone “better” that ??? So why the problem with audio. Okay use it without an A-G2 snubber and it’s liable to take off and behave an RF transmitter. The best SS designs are immune to this either. I use the KT88 up to 100Khz without snags, perhaps that’s down to how I use it. Skill ? perhaps positron you are right.......I’ve got so used to it.
I’m convinced that most of these “differing views” regarding output tubes (even mine scathing the EL34) should really be more directed to some miserably configured intermediate stages for creating the poor sound and lousy harmonics. Especially when the long tailed configuration is power drive and quenching Miller effect, effectively trying to do two jobs in one. I’m abs’ against this horror configuration unless followed by a non-loading driver stage....this may be the secret of best designs.
Sine wave tests on the Mullard 20Watt exposes a poor looking Lissajous pattern at 10Khz or in laymans’ terms the phase change is goes to pot contributing to THD. It’s not the phase change in the o/p transformer always to blame..... but unsymmetrical quenching of o/p tube Miller effect misbalancing the driver tubes creating a “phase hang-over” at HF leading to high THD.
Apply Miller effect theory (as used in Mosfet drive calculations) and then the impedance cum driver picture becomes clearer of what the drivers have to do. My version of Spice doesn’t uncover this pecularity.
This particular long-tailed pair design uses uses 180K resistors in the ECC83 phase splitter to effectively drive the EL34’s but have a look at the auto bias dampers 470K each....... an amp with overall high loop gain and 30dB feedback @1Khz.. The HF response is high but at very high THD creating a muddled sound.. Interestingly I’ve heard users replacing the EL34’s with KT66’s or even older 6CA7’s have obtained a “better imaged sound”. There is more to all of thisl.
I don’t want to daunt anyone wanting to make this design up as it’s an easy tame P-P starter amp and it will deliver the goods. The S/N is also very good at nearly –90dB below 20W but I don’t rate it at top end Hi Fi quality.
So back to the user of parallel EL34’s in multiple push-pull, it depends whether fixed bias or auto is used and use a good driver stage. One can use cathode followers for drive ease or a well designed high current driver a design sim to Williamson used, except with much lower resistor values.
It isn’t suprising that most of the push pull amp designs that use interstage drivers with a common cathode configuration (excellent C.M rejection) seem to be the best sounding performers.....Williamson etc....GEC88-50..so become not so dependant on the O/P tubes. The same drive comments goes for SE designs.
Comments welcome
Viva KT88’s 807’s
rich
As far as I know, KT88 has the innards of TT21, a transmitter tube competing with the 6146. All tubes that can operate with 800V plate.
KT88 is prone to parasitic oscillations requiring some care in the design at plate voltages above 450-500V.
In my opinion, KT88 has a hard sound in UL configurations. They sound better triode connected at around 525V.
I'm maintaining 2 pairs of Dynaco MKIII's owned by a couple of friends. One pair is equipped with GE 6550A's and the other pair with Sovtek 6550WGB's. Both sound better than with KT88's, in my and my friend's opinions. The pair with GE's the best despite the lowish bias due to wear (62mA instead of 70). This pair is modified using an ECC88 as input and paraphase splitter followed by 2 ECC82 SRPP drivers providing a nice low impedance drive to the 6550A's.
The Sovtek pair is modified using ECC83 in a cascode configuration followed by an ECC82 LTP. The Sovteks are problematic, I can't get a stable bias above 60 mA, they tend to run away. I have told my friend to modify the bias so the tubes can be biased individually to see if we can make them work better.
The 6550A pair already have separate bias and what I do is to first bias the tubes equally, then tweak one of the tubes to obtain 0V DC measured between the plates to reduce the residual DC current in the primary as much as possible. This does a LOT to the sound. It requires reasonably matched tubes with similar Ig2.
But on all listening sessions we have at my place when my friends visit me for rebiasing, I and they always agree that my EL34 amp sound better with softer more easy to listen to highs. I run them in UL with 350V, 330 ohms cathode bias and 68 ohms g2 resistors driven by a 6SN7 LTP and 6J5 input.
Parallel PP with EL34's can be tricky with parasitics as well. A small inductor in series with the plate of one of the EL34's in each half usually works, 1-2 uH or so.
To sum it up, I think KT88 and 6550 isn't for the beginner in tube amps. EL34 and 6L6GC are good tubes to start with. Always connect the EL34 supressor grid to the cathode though. Also always use a grid stopper resistor connected as close to the control grid pin as possible, 1k is a good value.
Just my 2 coins.
KT88 is prone to parasitic oscillations requiring some care in the design at plate voltages above 450-500V.
In my opinion, KT88 has a hard sound in UL configurations. They sound better triode connected at around 525V.
I'm maintaining 2 pairs of Dynaco MKIII's owned by a couple of friends. One pair is equipped with GE 6550A's and the other pair with Sovtek 6550WGB's. Both sound better than with KT88's, in my and my friend's opinions. The pair with GE's the best despite the lowish bias due to wear (62mA instead of 70). This pair is modified using an ECC88 as input and paraphase splitter followed by 2 ECC82 SRPP drivers providing a nice low impedance drive to the 6550A's.
The Sovtek pair is modified using ECC83 in a cascode configuration followed by an ECC82 LTP. The Sovteks are problematic, I can't get a stable bias above 60 mA, they tend to run away. I have told my friend to modify the bias so the tubes can be biased individually to see if we can make them work better.
The 6550A pair already have separate bias and what I do is to first bias the tubes equally, then tweak one of the tubes to obtain 0V DC measured between the plates to reduce the residual DC current in the primary as much as possible. This does a LOT to the sound. It requires reasonably matched tubes with similar Ig2.
But on all listening sessions we have at my place when my friends visit me for rebiasing, I and they always agree that my EL34 amp sound better with softer more easy to listen to highs. I run them in UL with 350V, 330 ohms cathode bias and 68 ohms g2 resistors driven by a 6SN7 LTP and 6J5 input.
Parallel PP with EL34's can be tricky with parasitics as well. A small inductor in series with the plate of one of the EL34's in each half usually works, 1-2 uH or so.
To sum it up, I think KT88 and 6550 isn't for the beginner in tube amps. EL34 and 6L6GC are good tubes to start with. Always connect the EL34 supressor grid to the cathode though. Also always use a grid stopper resistor connected as close to the control grid pin as possible, 1k is a good value.
Just my 2 coins.
......Jax...There is alot to your reply.....ah now the TT21 brute, 1.2kV 200 watt tube UX4 base. I can see the construction connection.......but I'm against too high B+, (makes PSU more awkward) and this is an area where design costs can be reduced.
You are right about KT88's sounding rather bright in mid upper range.......however for stage and power work this is often preferred. For Hi Fi, a little more roll off at the top end by increasing the global nfb cap value usually sorts this out.
I run my KT88's at 66mA quies @ 485V B+(UL AB2) and 95mA @250V B+ (class A UL). The business about the output tranny nulling; I find even the slightest unsymmetrial offset effects LF THD levels. When (UK) Gardener transformers (1970's) produced anb output tranny with a core gap, it was quite large. In effect the E&I have an inherent construction gap, but I'm suprised that you find it effects the sound. What make output tranny are you using ?
As to your comments regarding ECC82's, yes snap! I found this a failed configuration for longterm stability. I tried various config's using the 81's 85's & 88's but in the end I went to high power drive designs.
In the past, the ECC82 wasn't an easy tube to get the noise spec down.....unless made by original mullard........so the price went through the roof. So I drifted away from using it. As far as I can recollect, none of the substitutes made by other manu's come anywhere close to orig Mullard spec.
rich
You are right about KT88's sounding rather bright in mid upper range.......however for stage and power work this is often preferred. For Hi Fi, a little more roll off at the top end by increasing the global nfb cap value usually sorts this out.
I run my KT88's at 66mA quies @ 485V B+(UL AB2) and 95mA @250V B+ (class A UL). The business about the output tranny nulling; I find even the slightest unsymmetrial offset effects LF THD levels. When (UK) Gardener transformers (1970's) produced anb output tranny with a core gap, it was quite large. In effect the E&I have an inherent construction gap, but I'm suprised that you find it effects the sound. What make output tranny are you using ?
As to your comments regarding ECC82's, yes snap! I found this a failed configuration for longterm stability. I tried various config's using the 81's 85's & 88's but in the end I went to high power drive designs.
In the past, the ECC82 wasn't an easy tube to get the noise spec down.....unless made by original mullard........so the price went through the roof. So I drifted away from using it. As far as I can recollect, none of the substitutes made by other manu's come anywhere close to orig Mullard spec.
rich
Jax......Striking the iron while it's hot........ I'm having a go with a UK supplier regarding transformer sheet M6 quality.........longitudinal field distortion and low level remanence from laminations not properly annealed or pure. The result is an unsymmetrical and distorted hysteresis curve.
...Tricky subject...It seems differing tranny manu'rs use different thickness laminations, the 20u oxide film on each stamping acts as the eddy current break, the thickness in practice varies the inherent lamination air gap/ permeability/ end result = inductance. We aren't talking about massive variations, but subtle effects which influence sound quality. Thicker laminations with thicker oxide allow for slightly greater out-of-current balance in push-pull primary. Some manufacturers stack three laminations together then reverse, as often done in mains trannys. However, adding thicker laminations creates a slightly narrower hysteresis quadrant, lowering permeability resulting in more turns.
The way I see it, ye thinner the laminations, the more critical out-of-balance primary becomes. This might account for quality variations at low level signals at low output powers, which you mentioned. On the whole I prefer tranny's with thicker laminations which can accept higher Bmax and tolerate misbalanced primaries without muckin' up the sound quality. However compromises have to made all round and is much a personal choice of manufacturer......
However de-facto......Intermodulation and harmonic distortion, resulting from non-linearity between the mag current and the field in the output tranny. This is always present but is dependant on keeping Bmax low. An undersized core forced to run at a lower frequency will run at an higher eff Bmax with a corresponding increase in distortion.
So the solution for outstanding push-pull quality is to use a large core area which has the same effect as high inductance. This is an area where some manufacturers use different thickness laminations, thinner in the middle and thicker on the outers.
However it would be interesting to compare which output tranny you think sounds best with a corresponding look at the lamination thickness on a particular make. There ain't much in it.
Swedish and Japanese iron quality may account why Lars Lundahl trannys seem to sound the best........and +++$$$
From the pit ....rich
...Tricky subject...It seems differing tranny manu'rs use different thickness laminations, the 20u oxide film on each stamping acts as the eddy current break, the thickness in practice varies the inherent lamination air gap/ permeability/ end result = inductance. We aren't talking about massive variations, but subtle effects which influence sound quality. Thicker laminations with thicker oxide allow for slightly greater out-of-current balance in push-pull primary. Some manufacturers stack three laminations together then reverse, as often done in mains trannys. However, adding thicker laminations creates a slightly narrower hysteresis quadrant, lowering permeability resulting in more turns.
The way I see it, ye thinner the laminations, the more critical out-of-balance primary becomes. This might account for quality variations at low level signals at low output powers, which you mentioned. On the whole I prefer tranny's with thicker laminations which can accept higher Bmax and tolerate misbalanced primaries without muckin' up the sound quality. However compromises have to made all round and is much a personal choice of manufacturer......
However de-facto......Intermodulation and harmonic distortion, resulting from non-linearity between the mag current and the field in the output tranny. This is always present but is dependant on keeping Bmax low. An undersized core forced to run at a lower frequency will run at an higher eff Bmax with a corresponding increase in distortion.
So the solution for outstanding push-pull quality is to use a large core area which has the same effect as high inductance. This is an area where some manufacturers use different thickness laminations, thinner in the middle and thicker on the outers.
However it would be interesting to compare which output tranny you think sounds best with a corresponding look at the lamination thickness on a particular make. There ain't much in it.
Swedish and Japanese iron quality may account why Lars Lundahl trannys seem to sound the best........and +++$$$
From the pit ....rich
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