Here are a couple threads and some articles to get started:
Sony Vfet Illustrated build guide
Sony VFET Amplifier Part 2
http://www.firstwatt.com/pdf/art_sony_vfet_pt1.pdf
http://www.firstwatt.com/pdf/art_sony_vfet_pt2.pdf
http://www.firstwatt.com/pdf/art_diy_sony_vfet.pdf
PCBs for the 'diy' version is still available:
https://diyaudiostore.com/collections/printed-circuit-boards/products/sony-vfet-circuit-boards
Sony Vfet Illustrated build guide
Sony VFET Amplifier Part 2
http://www.firstwatt.com/pdf/art_sony_vfet_pt1.pdf
http://www.firstwatt.com/pdf/art_sony_vfet_pt2.pdf
http://www.firstwatt.com/pdf/art_diy_sony_vfet.pdf
PCBs for the 'diy' version is still available:
https://diyaudiostore.com/collections/printed-circuit-boards/products/sony-vfet-circuit-boards
@lhqam - Thanks for accommodating my order along with Dennis' and thanks for shouldering the work Dennis! 
and if you're game enough, you can try building the CSX1 (VFet v1) here:
http://www.firstwatt.com/pdf/art_sony_vfet_pt1.pdf
I've just finished this amp here and doing the touch ups (clear covers and labeling):
My Sony VFET CSX1 Adventures & Grief !
SIT3X boards were shipped today to:
- Russellc
- arky
- yoaudio
- PierreQuiRoule
- Dennis Hui
- jotom750
- iestynrw
- asanden
- Samuel Jayara
I am working on getting the BOMs up to date. Due some minor circuit changes, primarily the output stage optocoupler CTR, some resistor values must be changes. This is not a big deal, other than a change to probably only one resistor.
There are a number of options for the power supply, depending on the heatsink capacity of the chassis. Although I have not actually tested the SIT3X with heatsinks comparable to the DiyAudio Store 5U 400mm chassis, I think a 300VA transformer with 32Vrms secondaries per channel is appropriate and the OS stage bias can be adjusted for a suitable heatsink temperature. I prefer to use fan-cooled heatsinks, allowing higher voltage secondaries (36V) and higher bias currents.
There are a number of options for the power supply, depending on the heatsink capacity of the chassis. Although I have not actually tested the SIT3X with heatsinks comparable to the DiyAudio Store 5U 400mm chassis, I think a 300VA transformer with 32Vrms secondaries per channel is appropriate and the OS stage bias can be adjusted for a suitable heatsink temperature. I prefer to use fan-cooled heatsinks, allowing higher voltage secondaries (36V) and higher bias currents.
You can use them as a gain device as well. Check Michael Rothacher's LuminAria and my All SIT 50W+ amp thread. You can also find 2SJ28 thread. Excellent device, indeed.
Attached is a zip file containing the following BOMs (Bills of Materials):
- Text files for:
- SIT3X-OS (OS and cap multiplier parts).
- SIT3X-FCFE
- single channel power supply cap board
- dual channel power supply cap board
- XLS files that can be loaded into Mouser for:
- SIT3X-OS
- SIT3X-FCFE
A very timely release of information. 
I have a shiny set of new PCBs. Time to start looking at chassis and PSU build considerations.
I have a shiny set of new PCBs. Time to start looking at chassis and PSU build considerations.
Attached is a zip file containing information about the SIT3X Prototype power supply, chassis, and wiring, and the new SIT3X PCBs and power supply arrangements.
This is a first iteration of what should become a more complete build guide for the SIT3X. This zip file is missing the chassis details for the diyAudio Store 5U 400mm chassis.
Organization of the files in the zip file:
SIT3X-Build-Guide
This is a first iteration of what should become a more complete build guide for the SIT3X. This zip file is missing the chassis details for the diyAudio Store 5U 400mm chassis.
Organization of the files in the zip file:
SIT3X-Build-Guide
- SIT3X-Build-Guide/prototype
- chassis-wiring.jpg (Power supply and chassis wiring)
- heatsink-layout.jpg
- PS-panel-1.jpg
- back-panel.jpg
- bottom.jpg
- SIT3X-Build-Guide/power-supply
- single transformer 2-secondaries
- PS-caps2-20200818-1.pcb.jpg
- PS-2CH-20200830.BOM
- SIT3X-single-transformer-chassis-wiring-1NTC-20200902-2.asc.jpg
- SIT3X-single-transformer-chassis-wiring-2NTC-20200912-1.asc.jpg
- dual transformers 4-secondaries
- PS-caps1-20200818-1.pcb.jpg
- PS-1CH-20200830.BOM
- SIT3X-dual-transformer-chassis-wiring-20200830.asc.jpg
- single transformer 2-secondaries
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