A thought that came to my mind is,on the LL1663 Lundahl OPT:
http://www.lundahl.se/wp-content/uploads/datasheets/1663.pdf
There are 33% UL whereas others I belive have 43%,does this mean that 33% means lower output power?
And another thought:What is the difference soundwise on KT77 and KT66?
http://www.lundahl.se/wp-content/uploads/datasheets/1663.pdf
There are 33% UL whereas others I belive have 43%,does this mean that 33% means lower output power?
And another thought:What is the difference soundwise on KT77 and KT66?
With 33% you will have more power but more distortion; at 43% (standard tap, also called Partial triode) the tubes are working "similar" as a triode, lower Rp, better linearity, less efficency.
The KT77 and 66 are two different tubes ( same pinout) even are from same family, the KT77 can be used as replacement of 66 ( after the checksl on circuit) but viceversa nedd could not possible
Walter
The KT77 and 66 are two different tubes ( same pinout) even are from same family, the KT77 can be used as replacement of 66 ( after the checksl on circuit) but viceversa nedd could not possible
Walter
> 33% means lower output power?
No.
100% (triode mode) is low THD but very low power.
0% (pentode mode) is more power and low THD.
The range from 50% to 20% tap is all low THD with high power. The "exact optimum" within this zone depends on the tube-type and also what you want to optimize (Watts or THD), but there's really not a lot of difference all through this range.
I never heard of 33% taps but it seems a fine choice to me.
No.
100% (triode mode) is low THD but very low power.
0% (pentode mode) is more power and low THD.
The range from 50% to 20% tap is all low THD with high power. The "exact optimum" within this zone depends on the tube-type and also what you want to optimize (Watts or THD), but there's really not a lot of difference all through this range.
I never heard of 33% taps but it seems a fine choice to me.
Interesting, look at the bottom of the last page in Hafler & Keroes 1952 patent, and the 45% is of windings with a 20% tap for impedance.
The tubes specified are 6L6, 5881, 807, and KT-66
http://www.pearl-hifi.com/06_Lit_Ar...ol_01/Sec_02/073_Keroes_Hafler_UL_US_1955.pdf
I had some transformers wound by Edcor with 25% impedance taps vs the standard 40% taps but haven't had a chance to compare the two. Edcor will wind custom ratios, but charge a $40 setup fee (or did when I had mine made).
Here is an interesting quote from the patent:
The tubes specified are 6L6, 5881, 807, and KT-66
http://www.pearl-hifi.com/06_Lit_Ar...ol_01/Sec_02/073_Keroes_Hafler_UL_US_1955.pdf
I had some transformers wound by Edcor with 25% impedance taps vs the standard 40% taps but haven't had a chance to compare the two. Edcor will wind custom ratios, but charge a $40 setup fee (or did when I had mine made).
Here is an interesting quote from the patent:
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Few comments;
Real behaviour for most beam tubes are shown very well in Gunfu's post #5. It should however be noted that those graphs differ depending on the tube. In general, with pure pentodes e.g. EL34 output begins to fall immediately on moving the screen tap up from 0%, while with the Kt88 output actually rises slightly all the way up to a 40% tap, because of the contribution to output of the screen gird.
One must also be careful regarding change in distortion. The actual distortion keeps falling as one progresses to triode, but the percentage not necessarily, as the denominator in the fraction (output watts) also falls.
Furthermore, there is not a clear optimum percent screen tap as is often claimed. It depends on the tube, and 'optimality' is often academic. Characteristics change smoothly as the screen tap procedes from pentode to triode operation. (A tube's 'triode µ' has roughly to do with the 'optimum' performance, but it is more complicated.)
I will not be drawn into discussion regarding the original Hafler and Keroes patent description; much has been said elsewhere. Similarly The "sound" of one tube vs. another has more to do with the complete circuit design than this or that single feature. I have said elsewhere that what with a sometimes large spread in characteristics between types of the same brand these days, any noticed differences have often more to do with a particular tube's characterisitcs than with the type.
Lastly, figures for distortion are t.h.d. The actual composition of high order harmonics can give an audible result.
Real behaviour for most beam tubes are shown very well in Gunfu's post #5. It should however be noted that those graphs differ depending on the tube. In general, with pure pentodes e.g. EL34 output begins to fall immediately on moving the screen tap up from 0%, while with the Kt88 output actually rises slightly all the way up to a 40% tap, because of the contribution to output of the screen gird.
One must also be careful regarding change in distortion. The actual distortion keeps falling as one progresses to triode, but the percentage not necessarily, as the denominator in the fraction (output watts) also falls.
Furthermore, there is not a clear optimum percent screen tap as is often claimed. It depends on the tube, and 'optimality' is often academic. Characteristics change smoothly as the screen tap procedes from pentode to triode operation. (A tube's 'triode µ' has roughly to do with the 'optimum' performance, but it is more complicated.)
I will not be drawn into discussion regarding the original Hafler and Keroes patent description; much has been said elsewhere. Similarly The "sound" of one tube vs. another has more to do with the complete circuit design than this or that single feature. I have said elsewhere that what with a sometimes large spread in characteristics between types of the same brand these days, any noticed differences have often more to do with a particular tube's characterisitcs than with the type.
Lastly, figures for distortion are t.h.d. The actual composition of high order harmonics can give an audible result.
Perhaps risking over-exposure, but few more thoughts:
One needs to realise that a pentode with whatever kind of external NFB still has pentode characteristics, if reduced: relative sensitivity to operating point and load variations, possibility of higher order harmonic distortion etc. The UL mode has the combined advantages of triode and pentode 'internally' generated' before NFB (as a result of non-linear internal feedback or however one wants to see it). Measured performance indicates UL has a slight advantage over either triode or pure pentode characteristics - and with negligible extra effort.
Comparison to triode operation: At maximum available triode output watts, UL will have slightly lower distortion than triodes with same tubes; in addition then to making the extra watts available. (But a screen switching facility beteen triode and pentode does not necessarily render this; optimum conditions for these topologies are mostly not the same.)
Lastly, the difference in available output power is mostly <3 dB; generally agreed to be a low difference in loudness.
One needs to realise that a pentode with whatever kind of external NFB still has pentode characteristics, if reduced: relative sensitivity to operating point and load variations, possibility of higher order harmonic distortion etc. The UL mode has the combined advantages of triode and pentode 'internally' generated' before NFB (as a result of non-linear internal feedback or however one wants to see it). Measured performance indicates UL has a slight advantage over either triode or pure pentode characteristics - and with negligible extra effort.
Comparison to triode operation: At maximum available triode output watts, UL will have slightly lower distortion than triodes with same tubes; in addition then to making the extra watts available. (But a screen switching facility beteen triode and pentode does not necessarily render this; optimum conditions for these topologies are mostly not the same.)
Lastly, the difference in available output power is mostly <3 dB; generally agreed to be a low difference in loudness.
The effective plate resistance, rp, of Ultra-Linear wired Pentode or Beam Power tubes are often very approximately 2 times that of the same Pentode or Beam Power tubes that are in Triode-Wired mode.
Therefore, without negative feedback:
To have an equal damping factor for an Ultra-Linear circuit as the damping factor of a Triode-Wired circuit, you will have to use an Ultra-Linear transformer with plate to plate impedance that is 2 times higher than the transformer that is used for the same tubes in Triode-Wired mode.
But the 2 times increased plate to plate impedance of the Ultra-Linear transformer will reduce the output power of the Ultra-Linear amp.
It can be a trade off.
Power, distortion, negative feedback or no negative feedback, simplicity, complexity.
Therefore, without negative feedback:
To have an equal damping factor for an Ultra-Linear circuit as the damping factor of a Triode-Wired circuit, you will have to use an Ultra-Linear transformer with plate to plate impedance that is 2 times higher than the transformer that is used for the same tubes in Triode-Wired mode.
But the 2 times increased plate to plate impedance of the Ultra-Linear transformer will reduce the output power of the Ultra-Linear amp.
It can be a trade off.
Power, distortion, negative feedback or no negative feedback, simplicity, complexity.
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