JoaMat

I don't what chip it is. Marking might be???? Very hard to see. 26QH 288 A3HL Including in curcuit is also dual comparator 2093B and .05R sense resistor. Good luck and looking forward a report.

Nice idea. If you can implement an auto detect function as well – like Elekit has done with TU-8900. Power module… filament supply in black square, and the tiny - 2mm x 2mm - step-down converter.

You won’t find them boards at Kevin’s library. Custom made.

Check this link - lots of good stuff. There you find gg.zip .

Congratulations to the T2 build. Please, allow me to point out… the crossed/twisted legs of TTA004B/TTC004B that replace 2SK79/2SK216. Great work. No updated boards needed.

Did this today today – in full dayligt. Replaced EML 20B-V4 with 2A3 tubes in a Megatron with solid state constant current sources. Changes are filament voltage and cathode resistors (from 640 ohm to 3600 ohm. Only light is from blue and red LEDs and some light from the tubes themself.

Happy Birthday!

Thanks for comment and link to ROHM document, @simmconn. Very much appreciated. That test had obviously no chance to be successful.

Since I don’t know how to calculate the thermal resistance between to-252 and heat sink out into free air I made this small test. I got a clear answer. I do know Ohm's law though.

Thanks for notifying. The more eyes the better and… No, I missed that damage. With L-bracket it looks like this. Clearence between +400V area and ground is 40 mil. So, I doubt that there has been an electric short. I suspect that, for a reason I don’t understand, the current rushed and 10m90 quickly over heated. At the same time the PSU gave up and all went silent. I guess it’s heat from 10m90s that caused the damage. But that is a 100% guess. Anyhow, I think I stick to to220 version of 10m90s and forget this mishap.

Milled a small board to test IXCP10M90S(TO-252). Attached board to heat sink via L-bracket and sil pad for insulation purpose of course. When increasing current to 20 mA left side its 10m90s popped and left the board completely. Found it on floor. So, no more testing regarding surface mounted 10m90s. I’m very pleased with the new mini T2 board. Here with 300B via tube adapter with filament injection, 5VAC from transformer. Works great. Nice setup, don’t you think?

2n3904 does the same thing. Can be removed. Anyhow it won’t protect you from sudden shorts.

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.