I believe codyt got his 2SK79 from Jim's Audio when he built his SRPP preamp and his 2SK79 B1 buffer, and they seemed genuine. I bought mine from a diyAudio member. The were pulls from a non-functioning Sony amplifier.
My take on this is that although the 2SK79 is more expensive than common parts, they are still reasonable compared to some much sought after triode tubes. The solid state parts will also last a long time, probably for the rest of my life, whereas no matter how expensive the tube, it will degrade over time, dragging performance down with it, and will eventually need replacing.
And then because I built it myself the total cost was a few hundred dollars (not including the cost of the volume control transformers that I have owned for may years and were used in a former 26 preamp build). To buy something like this commercially assuming that it would be available would probably be in the thousands of dollars. That's the beauty of DIY. And to top it off, I really like its sound.
If you don't have 2SK79 but have other Sony VFETs such as 2SK60, 2SJ18, 2SK82, or 2SJ28, they can be used to build a preamp too. Perhaps the smaller Tokins too.
And then there is ra7's Schade preamp too.
My take on this is that although the 2SK79 is more expensive than common parts, they are still reasonable compared to some much sought after triode tubes. The solid state parts will also last a long time, probably for the rest of my life, whereas no matter how expensive the tube, it will degrade over time, dragging performance down with it, and will eventually need replacing.
And then because I built it myself the total cost was a few hundred dollars (not including the cost of the volume control transformers that I have owned for may years and were used in a former 26 preamp build). To buy something like this commercially assuming that it would be available would probably be in the thousands of dollars. That's the beauty of DIY. And to top it off, I really like its sound.
If you don't have 2SK79 but have other Sony VFETs such as 2SK60, 2SJ18, 2SK82, or 2SJ28, they can be used to build a preamp too. Perhaps the smaller Tokins too.
And then there is ra7's Schade preamp too.
So to check a LTSPice simulation result, I changed the right channel buffers' V+ to 98V while keeping the 2SK79 V+ at 144V, as the simulation showed lower distortion than with V+ at 144V to both 2SK79 and buffers. It involved a bit more than just changing the voltage but long story short, the measured harmonic distortion was slightly lower, but at high voltage output, higher harmonics became prominent, similar to what was measured when I had the 2SK79 at V+ 98V and Vd 65V (post #36 - prominent higher harmonics at 20Vrms output).
So I went back to V+ 144V for buffers and 2SK79 (post #37). With that decision made, I modified the left channel circuit to match the right channel.
I ran distortion measurements for the left channel and here are the results. The left channel had much lower distortion, most likely due to both 2SK79 not being identical. See post #37 for the right channel's distortion. I have also added 5Vrms and 25Vrms measurements for the right channel for comparison.
I do not know whether the difference between the two 2SK79 is due to the 2SK79 manufacturing tolerances or perhaps the right channel 2SK79 had suffered some deterioration during its life. After all, they had already served some time in a Sony VFET amplifier before they were sold to me. I have no complaints with the sound so I am not going to try to find a replacement 2SK79 to lower the right channel's distortion.
In fact I am actually quite happy with the sound so no more tweaking of this preamp. It is finished. Currently it is feeding my summer amp, the 10W single ended 2SJ28 choke loaded follower, and they sound great.
It also has enough gain and voltage output to power my 50 Watt THF-51S Mu-Follower Follower monoblocks to full power. I do not need 50 Watts - most of the time my amps are probably sending less than one Watt to my 103dB speakers. But this is DIY, so more is better, and the fun is in the journey.
So I went back to V+ 144V for buffers and 2SK79 (post #37). With that decision made, I modified the left channel circuit to match the right channel.
I ran distortion measurements for the left channel and here are the results. The left channel had much lower distortion, most likely due to both 2SK79 not being identical. See post #37 for the right channel's distortion. I have also added 5Vrms and 25Vrms measurements for the right channel for comparison.
I do not know whether the difference between the two 2SK79 is due to the 2SK79 manufacturing tolerances or perhaps the right channel 2SK79 had suffered some deterioration during its life. After all, they had already served some time in a Sony VFET amplifier before they were sold to me. I have no complaints with the sound so I am not going to try to find a replacement 2SK79 to lower the right channel's distortion.
In fact I am actually quite happy with the sound so no more tweaking of this preamp. It is finished. Currently it is feeding my summer amp, the 10W single ended 2SJ28 choke loaded follower, and they sound great.
It also has enough gain and voltage output to power my 50 Watt THF-51S Mu-Follower Follower monoblocks to full power. I do not need 50 Watts - most of the time my amps are probably sending less than one Watt to my 103dB speakers. But this is DIY, so more is better, and the fun is in the journey.
Attachments
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2SK79 Preamp Left Channel V+ 144V Iq 3.5mA 1.0Vrms.jpg -
2SK79 Preamp Left Channel V+ 144V Iq 3.5mA 5.0Vrms.jpg -
2SK79 Preamp Left Channel V+ 144V Iq 3.5mA 10.0Vrms.jpg -
2SK79 Preamp Left Channel V+ 144V Iq 3.5mA 20.0Vrms.jpg -
2SK79 Preamp Left Channel V+ 144V Iq 3.5mA 25.0Vrms.jpg -
2SK79 Preamp Rightt Channel V+ 144V Iq 3.5mA 5.0Vrms.jpg -
2SK79 Preamp Rightt Channel V+ 144V Iq 3.5mA 25.0Vrms.jpg
Hi everybody,
I'm working on a project, using these transistors as a first voltage gain stage of SE no FB class A amplifier.
The second stage is a source follower with Exicon lateral MOSFETs. The supply voltage for the first stage
is similar, in my case the Vds is about 92-93V, Uds is 50V, but drain current is higher - 8-9mA, as the input
impedance of laterals is relatively low, (2x8A transistors in parallel). The transistor is mounted on a small
PCB heatsink. The project is almost done, only very few mechanical works left.
For me the advantage of these v-FETs is to use them with a simple passive load, only a drain resistor and
without any negative feedback. As they are a bit noisy, it'll be better to use them with higher input signals
- 0.5-1V, i. e. your RIAA preamp should work much better with real vacuum valves š
P.S. I bought my transistors from jim's audio, on ebay, so they are genuine, not fake.
If somebody wants to sell some of his v-fet stuff for a reasonable price, please PM me.
I'm working on a project, using these transistors as a first voltage gain stage of SE no FB class A amplifier.
The second stage is a source follower with Exicon lateral MOSFETs. The supply voltage for the first stage
is similar, in my case the Vds is about 92-93V, Uds is 50V, but drain current is higher - 8-9mA, as the input
impedance of laterals is relatively low, (2x8A transistors in parallel). The transistor is mounted on a small
PCB heatsink. The project is almost done, only very few mechanical works left.
For me the advantage of these v-FETs is to use them with a simple passive load, only a drain resistor and
without any negative feedback. As they are a bit noisy, it'll be better to use them with higher input signals
- 0.5-1V, i. e. your RIAA preamp should work much better with real vacuum valves š
P.S. I bought my transistors from jim's audio, on ebay, so they are genuine, not fake.
If somebody wants to sell some of his v-fet stuff for a reasonable price, please PM me.
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Hello Ben Mah,
Yesterday my friend gave me a quad 2SK79, I remebered my DHT preamp before, and I though it could be a good replacement for triode and just need change Vd 65~75V 3.5mA as well as Rs ~ 330R. I will try it out and get the results.
Yesterday my friend gave me a quad 2SK79, I remebered my DHT preamp before, and I though it could be a good replacement for triode and just need change Vd 65~75V 3.5mA as well as Rs ~ 330R. I will try it out and get the results.
Looks interesting. I used to have a 26 preamp during my tube days.
Looking at the schematic I am not sure that you need to change R5. R5 (10R) appears to be used to measure the current.
The gyrator provides the drain/anode load.
It is a mu follower so perhaps adjustment to R7 may be beneficial (or not). I do not have the expertise to advise on that.
Bartola 01a Preamp
Looking at the schematic I am not sure that you need to change R5. R5 (10R) appears to be used to measure the current.
The gyrator provides the drain/anode load.
It is a mu follower so perhaps adjustment to R7 may be beneficial (or not). I do not have the expertise to advise on that.
Bartola 01a Preamp
The 01A in the schematic uses filament bias, so Rf (20 ohms) will also need changing. Filament bias relies on the filament current which is substantially more than that of the tube.
Yah, I made a confusion . It shoud be changed to Rf~330R and coupled by a capacitor. Additionally, Ale decribed it in more detail, Rmu ranging from 470 to 1K5
Hybrid Mu-follower Output Impedance
Hybrid Mu-follower Output Impedance
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I didn't make the transistion from filament (Rf) to source (Rs), so I was fooled, too. Looks like you have things under control.
I was confused too. I thought Rs was R5.
Perhaps a trimmer resistor could be used for Rs to set the current.
Perhaps a trimmer resistor could be used for Rs to set the current.