JoaMat

Well, I consulted the old KGST folder on my computer and it looks like the first versions of KGST were with uncascoded 10M90S. Here is a picture from the KGST folder. KGST with smd parts, servo and uncascoded 10M90S. The designer is, the one and only@Kerry! See this post. Unfortunately, the pictures are gone. Board size said to be 2" x 4.5"

You might say I follow the strategy of DIY T2 PSU by Kevin. I have two PSU I’m using for all my electrostatic amplifiers. One original T2 PSU and one I made myself basically same as the original but with KGSSHV PSU regulators. Bottom line: I’ve never have bother about grounding strategies. So far, I haven’t had any issues with ground loops that I’m aware of.

I like the idea about to-252. First draft… …have to think about this. XLR ground pin to signal ground on PCB.

mini T2 with new boards. STN9360 replacing the obsolete KSA1156. Here the 01N100D are replaced with 10M90S and it works all right. The amplifier is configured for EL34/6CA7. Amplifier for 300B by member mla a few posts up. He also have 6A3 - see if he can be persuaded to test them.

No change needed. With LT1021-10volt the current is 10V/787ohm + 1 mA from ground pin = 13.7mA. One builder increased current to 18mA by changing resistor to 590R. Now I use 590 as well in my mini T2 DHT with Emission Labs tubes and I’m happy.

If problem to find 01n100d go for 10m90s. Works great in Sweden. Also, STN9360 (replacing KSA1156) seems to work.

I have no boards left. Last pair sent to Finland some months ago. I’m working on an updated version of mini T2 boards. A senior Head Caser is test building - he has not approved the boards yet. I use a Gilmore DIY T2 PSU for all my electrostatic amplifiers including mini T2. But you probably want to use something more suitable. There are several PSU boards to choose from here https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW?usp=sharing .

mini T2 ver.25 is starting to take its final shape, I think. I'm filing a little now and then. A small test board made now after coffee... here with UX4 socket. The connectors are from Electrokit https://www.electrokit.com/pcb-hane-5.08mm-2-pol-lagprofil and https://www.electrokit.com/skruvplint-pluggbar-5.08mm-2-pol-lagprofil. It is possible to use a regular 2-pole screw terminal, but I think the connectors in the pictures are much more practical. The circuit board connector in the pictures is notched in each lower corner with a sharply sharpened Japanese master chef's knife to fit between the solder islands. P.S. AI translated - I'm lazy

mini T2 board prepared for octal or UX4 sockets. Octal socket overlapped with UX4 (red arrows). If EML 20B-V4 or 300b/2A3 remove components at red arrows. If 300B/2A3 tie pads in green boxes together.

Welcome to HeadCase @EchoRoot Check below two links: https://drive.google.com/drive/folders/1r3g2TAtBUaBdiMorTWX7yYgeJ7maQbYW?usp=sharing https://drive.google.com/drive/folders/152thxfZafBmisG0CKCv6X82V-Ch9TjMH?usp=sharing

I believe you should move 22K resistor right tube to between G1 and 20BV4 pad. Then wire the 20BV4 pads together for bort EL34 and 20B-V4.

Yes. Upper left tube: from pin1 (G3) is a blue trace connecting Pin3 (A) - must be cut, but you probably have done that. Really an exciting project.

Done some more work. Added a couple of zero ohm resistors round the output tubes and a few other changes. If 20B-V4 tube remove the zero ohms and 220R resistors. Pcb layout is more fun than Sudoku.

Below is my way to describe how to prepare mini T2 for EML 20B-V4. Cut traces to Pin1 (G3). Cut traces at heater pins connected to resistor string 120K, 300K, 300K, 300K (one per channel). Purpose of the sting is to create -400V potential for Pin5 (G1) via 22K resistor. Remove 220R resistors. Remove 22K resistor Find a solution to put 22K resistors from Pin5 (G1) to resistor string between 120K and 300K resistors. This is probably the trickiest part. No heater wires between tubes of course. I’m sure you can modify your mini T2 to take the 20B-V4 tubes. But, maybe one should make a new board for the Emission Labs tubes… Not much heat produced by DC-DC converter supplies. No heat sinks needed.

Tanks for the schematic. The DC-DC converter itself is 62mm x 26mm. Board with rectifiers, electrolytics and converter module is 91mm x 33mm per section. No changes to the circuit more than the tube change and its filament arrangement.