I know that they're not common.But you can order a custom one from the most companies out there.I think Plitron have some standard types,GK xformers and Lundahl.
The internal feedback of a triode isn't linear in all frequencies.This is the major problem of a triode.
With a pentode in CFB,you have very good linearity even below and above the standard 20hz-20Khz.
I'm not an SE fan so I haven't try it.My amp is a pure class A 6550 P-P with CFB.I have 20W undistorted even when the load falls to 2 ohms!
A friend of mine has built an SE amp with a pentode in CFB configuration that really kicks.He uses an SV6550.
7 to 8 watts,like 300B but it drives 4 ohm speakers for fun.
The internal feedback of a triode isn't linear in all frequencies.This is the major problem of a triode.
With a pentode in CFB,you have very good linearity even below and above the standard 20hz-20Khz.
I'm not an SE fan so I haven't try it.My amp is a pure class A 6550 P-P with CFB.I have 20W undistorted even when the load falls to 2 ohms!
A friend of mine has built an SE amp with a pentode in CFB configuration that really kicks.He uses an SV6550.
7 to 8 watts,like 300B but it drives 4 ohm speakers for fun.
Konnichiwa,
This assertation ("internal feedback of a triode") is at best poor science. There is no "Feedback" in the triode. It was merely observed (many decades ago) that a triode behaves SOMEWHAT analog to a pentode with looped feedback. That is a considerably different issue and to simply equate one with the other is wrong.
Further, the key area in the triode where the linearity becomes frequency dependent is due to the input capacitance and the (miller amplified) modulation of this capacitance due to the non-linear anode curves. Again, there is no "feedback" involved.
The result is that adding looped feedback to a pentode does not make it a triode.
So do you with a triode.
A Pentode with CFB or CFB & G2FB is a cheap way to realise a pretty decent, inexpensive amplifier, no more and no less.
No doubt nice. But have you compared it to a nice 300B, Class Push-Pull Amplifier, designed to similarly high standards (including for example crosscoupled, split load)?
Undistorted? I understand you mean with relatively little distortion. But what about the spectrum of this distortion? And exactly what is your definition? Further, what makes you believe a PP Amplifier with a pair of 300B Triodes could not deliver 20W into 2 Ohm with low distortion (it of course can do that, assuming competent design).
Kicks? Compared to what? A well designed 300B SE Amplifier? And in what sense, sonically or on the testbench?
Note, I am not rubbishing the KT88/6550 with CFB or in LM3 Mode. In fact, I'd probably recommend such an Amplifier as good "Beginners" item as it delivers good sound with inexpensive valves and re-usable transformers (ideally a 2k5:16R SE Transformer with a ultralinear tap, the 16 Ohm secondary used as CFB winding and the UL Tap for feedback to the screengrid), but I am questioning that you have sufficient comparisons to well designed, triode output based amplifiers and I question some of the theories you have mentioned.
But all told I'd probably recommend the JE-Labs 300B Amp discussed here over the KT88 based one IF the desire is to build only one Amplifier for best sonics AND these two choices are the ONLY ones available. (please note all the given qualifications).
Sayonara
PS, tried EL34 in LM3 Mode, UL and triode, PP & SE, SE Triode was best but 300B SE was much better and I'd wager the same holds for KT88/6550.
GAK said:
This assertation ("internal feedback of a triode") is at best poor science. There is no "Feedback" in the triode. It was merely observed (many decades ago) that a triode behaves SOMEWHAT analog to a pentode with looped feedback. That is a considerably different issue and to simply equate one with the other is wrong.
Further, the key area in the triode where the linearity becomes frequency dependent is due to the input capacitance and the (miller amplified) modulation of this capacitance due to the non-linear anode curves. Again, there is no "feedback" involved.
The result is that adding looped feedback to a pentode does not make it a triode.
GAK said:
So do you with a triode.
A Pentode with CFB or CFB & G2FB is a cheap way to realise a pretty decent, inexpensive amplifier, no more and no less.
GAK said:
No doubt nice. But have you compared it to a nice 300B, Class Push-Pull Amplifier, designed to similarly high standards (including for example crosscoupled, split load)?
GAK said:
Undistorted? I understand you mean with relatively little distortion. But what about the spectrum of this distortion? And exactly what is your definition? Further, what makes you believe a PP Amplifier with a pair of 300B Triodes could not deliver 20W into 2 Ohm with low distortion (it of course can do that, assuming competent design).
GAK said:
Kicks? Compared to what? A well designed 300B SE Amplifier? And in what sense, sonically or on the testbench?
Note, I am not rubbishing the KT88/6550 with CFB or in LM3 Mode. In fact, I'd probably recommend such an Amplifier as good "Beginners" item as it delivers good sound with inexpensive valves and re-usable transformers (ideally a 2k5:16R SE Transformer with a ultralinear tap, the 16 Ohm secondary used as CFB winding and the UL Tap for feedback to the screengrid), but I am questioning that you have sufficient comparisons to well designed, triode output based amplifiers and I question some of the theories you have mentioned.
But all told I'd probably recommend the JE-Labs 300B Amp discussed here over the KT88 based one IF the desire is to build only one Amplifier for best sonics AND these two choices are the ONLY ones available. (please note all the given qualifications).
Sayonara
PS, tried EL34 in LM3 Mode, UL and triode, PP & SE, SE Triode was best but 300B SE was much better and I'd wager the same holds for KT88/6550.
Hmmm
If you want colored, sheen, thin music, by all means go for a 300b amp. In all my years of listening, haven't heard one yet that didn't color the music. Slow and lacks emotion (indicates a lack of flat response and lack of true inner detail too. )
"Kicks? Compared to what? A well designed 300B SE Amplifier? And in what sense, sonically or on the testbench?"
The 300bs amps I have heard over the years aren't that dynamic either.
Note, I am not rubbishing the KT88/6550 with CFB or in LM3 Mode. In fact, I'd probably recommend such an Amplifier as good "Beginners" item as it delivers good sound with inexpensive valves and re-usable transformers (ideally a 2k5:16R SE Transformer with a ultralinear tap, the 16 Ohm secondary used as CFB winding and the UL Tap for feedback to the screengrid),..
I also think triode mode is sonically better, but with those low P-P parameters, he surely won't optimize the sound of his UL.
If you want colored, sheen, thin music, by all means go for a 300b amp. In all my years of listening, haven't heard one yet that didn't color the music. Slow and lacks emotion (indicates a lack of flat response and lack of true inner detail too. )
"Kicks? Compared to what? A well designed 300B SE Amplifier? And in what sense, sonically or on the testbench?"
The 300bs amps I have heard over the years aren't that dynamic either.
Note, I am not rubbishing the KT88/6550 with CFB or in LM3 Mode. In fact, I'd probably recommend such an Amplifier as good "Beginners" item as it delivers good sound with inexpensive valves and re-usable transformers (ideally a 2k5:16R SE Transformer with a ultralinear tap, the 16 Ohm secondary used as CFB winding and the UL Tap for feedback to the screengrid),..
I also think triode mode is sonically better, but with those low P-P parameters, he surely won't optimize the sound of his UL.
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