Now check this one out..... exactly the kind of design I was thinking of. 
http://www.geocities.com/Tokyo/5913/hybrid.html
http://www.geocities.com/Tokyo/5913/hybrid.html
If that is so, than I guess I will have to take a look at your schematic, the convenience of the other one is that it uses a 6SN7 which I have pleanty of.
I am also trying to keep the circuit simple, it is much easier to construct, and I need to keep the power at 100 watts in order for the metres on the LXI amplifier to be compatible.
The other problem I am worried about is how much heat will be produced, the heat sink is U shaped about 40cm long 8cm tall 4cm wide and half a cm thick, with the old amplifier schematic I have posted the amplifier basically stayed at 25 degrees C, never had it get all that warm even when I was hard on the amp.
So if you want you can ither email me the schematic at: amacrae@ns.sympatico.ca or you can post it here as I would be very interested to see what kind of design you have, building a class "A" amp will be later, when I find a decent heatsink.
Thanks sajti
I am also trying to keep the circuit simple, it is much easier to construct, and I need to keep the power at 100 watts in order for the metres on the LXI amplifier to be compatible.
The other problem I am worried about is how much heat will be produced, the heat sink is U shaped about 40cm long 8cm tall 4cm wide and half a cm thick, with the old amplifier schematic I have posted the amplifier basically stayed at 25 degrees C, never had it get all that warm even when I was hard on the amp.
So if you want you can ither email me the schematic at: amacrae@ns.sympatico.ca or you can post it here as I would be very interested to see what kind of design you have, building a class "A" amp will be later, when I find a decent heatsink.
Thanks sajti
Another Hybrid Design
I’ve been reading this thread with some interest. For anyone interested in an amplifier with an excellent hybrid design, Kevin Carter of K&K Audio has designed upgrades for the venerable Dynaco ST70. The design makes excellent use of solid-state devices and vacuum tubes combined to work in a circuit topology that is radically different and bears no resemblance to the original ST-70. In my opinion, the word “upgrades” is a misnomer. The design is more than sufficient to stand on its own without being tied to the ST70 in any way.
Kevin’s impressive sounding, pure Class A design uses a Lundahl amorphous core input transformer for phase splitting in place of 7199 tubes. Kevin has determined that, besides achieving very accurate phase splitting across the bandwidth, the input (or interstage) transformer “provides galvanic isolation between the source and the amplifier, removing the possibility of ground loop hum involving the power amplifier…” Following the input transformer, a pair 6N23P (6922)tubes is used in a differential stage to drive the EL34 output tubes through four coupling capacitors. According to Kevin “this input stage provides relatively high gain and very symmetrical drive to the output stage at a moderately low impedance.”
In the differential PP output stage, a pair of paralleled current sources (DN2540NS) is used, to which both cathodes of the EL34s have been connected. EL34 bias is adjusted by setting the current sources for the bias current of your choice. Besides operating the input stage as a Class A differential amplifier, the output stage also is true Class A differential and can be configured to operate in ultralinear (35w per channel) or pure triode mode. No global feedback is used. Kevin also explains: “Operating the output stage differentially also means that the output tubes "track" each other dynamically (as well as their initial matching allows.) This lowers distortion and dramatically improves sound quality..."
The power supply is robust and made simple by virtue of the good power supply rejection provided by differential amplifiers.
The modified ST70 sounds very dynamic and its 10W per channel (triode connected) must be heard to be appreciated. The sound is very open, airy, transparent and musical. To my ears, it rivals some very good single-ended amps. 10 watts don’t tell the whole story. There is more than enough power to drive my pair of 90dB Green Mountain Audio EOS HD monitors effortlessly.
Kevin currently sells an upgrade kit that can be purchased in various configurations depending on budget and performance needs. Although the original A470 OT is very good (to some, even ‘legendary’) the kit can also be used with modern transformers in the chassis of your choice.
Link: http://www.kandkaudio.com/poweramplifier.html
Disclaimer: I have no commercial ties with KandKAudio. This post is intended only to provide a response to this thread by sharing personal experience gained from a DIY project.
I’ve been reading this thread with some interest. For anyone interested in an amplifier with an excellent hybrid design, Kevin Carter of K&K Audio has designed upgrades for the venerable Dynaco ST70. The design makes excellent use of solid-state devices and vacuum tubes combined to work in a circuit topology that is radically different and bears no resemblance to the original ST-70. In my opinion, the word “upgrades” is a misnomer. The design is more than sufficient to stand on its own without being tied to the ST70 in any way.
Kevin’s impressive sounding, pure Class A design uses a Lundahl amorphous core input transformer for phase splitting in place of 7199 tubes. Kevin has determined that, besides achieving very accurate phase splitting across the bandwidth, the input (or interstage) transformer “provides galvanic isolation between the source and the amplifier, removing the possibility of ground loop hum involving the power amplifier…” Following the input transformer, a pair 6N23P (6922)tubes is used in a differential stage to drive the EL34 output tubes through four coupling capacitors. According to Kevin “this input stage provides relatively high gain and very symmetrical drive to the output stage at a moderately low impedance.”
In the differential PP output stage, a pair of paralleled current sources (DN2540NS) is used, to which both cathodes of the EL34s have been connected. EL34 bias is adjusted by setting the current sources for the bias current of your choice. Besides operating the input stage as a Class A differential amplifier, the output stage also is true Class A differential and can be configured to operate in ultralinear (35w per channel) or pure triode mode. No global feedback is used. Kevin also explains: “Operating the output stage differentially also means that the output tubes "track" each other dynamically (as well as their initial matching allows.) This lowers distortion and dramatically improves sound quality..."
The power supply is robust and made simple by virtue of the good power supply rejection provided by differential amplifiers.
The modified ST70 sounds very dynamic and its 10W per channel (triode connected) must be heard to be appreciated. The sound is very open, airy, transparent and musical. To my ears, it rivals some very good single-ended amps. 10 watts don’t tell the whole story. There is more than enough power to drive my pair of 90dB Green Mountain Audio EOS HD monitors effortlessly.
Kevin currently sells an upgrade kit that can be purchased in various configurations depending on budget and performance needs. Although the original A470 OT is very good (to some, even ‘legendary’) the kit can also be used with modern transformers in the chassis of your choice.
Link: http://www.kandkaudio.com/poweramplifier.html
Disclaimer: I have no commercial ties with KandKAudio. This post is intended only to provide a response to this thread by sharing personal experience gained from a DIY project.
I don't like to call my designs that use both sand and glass "Hybrid".
Why?
Because "hybrid" is a spoiled word; sometimes people blindly mix tubes and transistors in schematics that are optimal for transistors. For example: typical transistor opamp with tube LTP. Or, typical transistor symmetrical class AB output stage with tube VAS. Such designs never sound good because they don't address the main criterion: getting less of audible distortions using best abilities of both worlds. Instead, they mix tube-specific distortions with opamp-specific ones producing something that being called "Hybrid Amp" turn people against hybrid amps that are designed completely differently.
Why?
Because "hybrid" is a spoiled word; sometimes people blindly mix tubes and transistors in schematics that are optimal for transistors. For example: typical transistor opamp with tube LTP. Or, typical transistor symmetrical class AB output stage with tube VAS. Such designs never sound good because they don't address the main criterion: getting less of audible distortions using best abilities of both worlds. Instead, they mix tube-specific distortions with opamp-specific ones producing something that being called "Hybrid Amp" turn people against hybrid amps that are designed completely differently.
Hybrid Amplifier Clarification
JLH, thanks for the clarification
Wavebourn, thanks for your input. I understand your problem with the use of the word "hybrid". I can say with assurance that in the case of the K&K audio ST70 upgrade design, careful attention was given to using the "best ablilities" of both tubes and solid state devices to attain the best sound. Their respective strengths were implemented appropriately. To my ears, the proof is in the listening. However, because the perception of sound, especially reproduced recorded music, is subjective, to each his own.
JLH, thanks for the clarification
Wavebourn, thanks for your input. I understand your problem with the use of the word "hybrid". I can say with assurance that in the case of the K&K audio ST70 upgrade design, careful attention was given to using the "best ablilities" of both tubes and solid state devices to attain the best sound. Their respective strengths were implemented appropriately. To my ears, the proof is in the listening. However, because the perception of sound, especially reproduced recorded music, is subjective, to each his own.
sajti said:
You may use tubes and transistors such a way their distortions are minimal, or you may use they such a way so their distortions will be maximal. Why I started developing hybrids, because eliminating transformers by using CCS loaded source followers I got rid of transformers' specific distortions. Loading tubes on CCS or gyrator I extend their linearity. And so on. Not any combination of tubes and transistors lead to bad results, as well as not any combination of tubes and transistors lead to good results. What leads to good results, is such combination that helps to achieve more linear transfer function.
But as soon as bad hybrids (AB outputs to eliminate costs of transformers) appeared before good hybrids (combination of sand and glass for cleaner reproduction) the word is spoiled, and people don't see the difference (though refuse to listen to it).
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