JoaMat

I believe ver 2.0 is taken – Kerry’s shrinked smd…

My T2 PSU differs some from the original DIY T2 PSU as I have a -560V section which is as capable as the -500V. So with this modification the only work the -500v is doing is to set the 6CA7 G1 potential. LTspice simulation I’ve done indicates that -500V at G1 might be desirable. But I don't trust myself doing this kind of work in LTspice. Below schematic: removed Q24,Q25,Q28,Q29,LED, R48,R49. Added jumpers between drain k216 and cathode 6CA7.

I had to open up the KGST for adjustment since I lowered the rail voltages. Four plain old good trimmers. My right foot for size comparison.

Thanks a lot George, but I actually have a small stock of j79/k216 myself. Living in the middle of nowhere you need to be prepared. Have been socializing with the faulty channel today and we are now both happy again. Maybe it’s more of a Grounded Grid with dual tube input and active batteries than a T2. Picture below shows the modded T2. No j79/a1486 at the output stage. Upper right the middle a1486 is missing – replaced with resistor so upper tube grid voltage is set by a voltage divider. If you have a well defined supply voltage you don’t need to send 2.5mA through a 27K resistor – I think.

Happy Birthday!

If running short of 2sj79 one could rebuild the T2 to something similar to a Grounded Grid. I removed j79s, 750R resistors, a1486s and corresponding LED. Works/ed like charm. Unfortunately right channel started to obstruct after a while. Perhaps this kind of modification isn’t appropriate. For the time being I run left channel to both sides.........

MINIWATT tubes - Nice!

Draft of dual 6922 input (similar to T2 input), with current tunnel (as Carbon etc.) Voltage cross 2sa1486 580V and 700mW of heat.

Kerry, do you hear any bump or whistle in the headphone when power off with the servo?

Make your pick. Then Whitigir build the other.

I suggest a Sandwich.

Suddenly left channel went down – turned out that one mosfet 2sj79 had transformed itself to a PNP.

Nice. Like the 08N100D up there. IC1 is?

Reduced voltage on my “modified” T2. DHT by night.

@@bui501, I’ve no idea if the PBHVs will do or not – someone should try. But how about KSA1156? Max voltage cross pnp in battery is around 370V. As for space it might be a little tight though. The squirrels sit on them.

Here is a link to a post. In that post there is a link to a BOM. In that BOM you find LTL-4213. I’ve two different BOMs on my computer from the same topic, both with LTL-4213.

The first electrostatic amplifier I built was the first version of KGSSHV with onboard heat sinks and I used LTL-4213 LED forward voltage 2.1V. At that time the suggested LED was LTL-4213 which also was used in the DIY T2. I’m aware of that some builders stick to LED with lower voltage. My experience is that you very well can use the “higher voltage” LED without changing resistors.

Voltage cross the resistor is LED voltage minus base-emitter voltage - roughly 1.9V – 0.6V = 1.3V. So approximately current through R33/Q17 2.5 mA (RV2 centered) and R50/Q20 4mA. Those values will depend on the individual components.

Very nice indeed! Like them Blue (Hawaii) lights.

1A at 450V – yeh, that’s a pretty decent load

Wow, that’s wonderful! U1 - op amp in sot23-5 package, any suggestion?

Yes, it’s the same SMD transistor. I just soldered them in standing to save space. As a DIYer you are entitled to do whatever you want. If going "through hole parts" I like that layout a lot. Then one should change 2sa79/2sk216 to ksa1229a/ksc2690c and make output stages cascode current sources. That would be a great amplifier with available parts at reasonable prices.

Yep, I remember you used a trimmer – that’s why I came to use trimmer on my modified T2. I think working voltage 50 V will do. Try the servo - it's easily done. Thanks Kerry, LTspice is really a very useful tool. I’ve deliberate skipped the D2 zener (Kevin uses the Zener) to see what happens and so far no failures. The R29 resistor is probably a good idea but I’ve skipped that too as the servo seems to work all right without it. As for C1 I use 1uF/50V in my Carbon and GG with tube input (same as Kevin later designs). But on the T2 I had some problem with 1uF so after some testing I ended up with 6.8uF (have just opened the amp to check). Regarding the 2.2pF – I actually added more capacitance to reduce some oscillation at outputs seen on the oscilloscope. I probably better go back and have look at it again. DIY is fun

Below is a picture of my modified DIY T2. Zoom in and you can finds several resistors standing. There are also standing STN9360. You won’t find other types of STN9360. Those homemade boards have been in service for four years now. I’ve made several modifications and the boards have been very kind to me. Kevin’s t2shrinkedv10 is based on my home cooked boards. I’m confident his board is OK. But be aware if something goes wrong it could be a tricky thing working on that board as some areas are pretty crowded. Today I would make a different layout of the board as I find the board a bit obsolete.

Above post show changes to the balance servo I’ve made. Below schematic shows changes made to get the KGOOS (Opto Offset Servo) - the only offset servo you need. Q33 and R73 replaced by a small daughter board and the resistor strings changed accordingly. For reference here is t2schemop.pdf, schematic of the STAX T2 output section. Drawn by Kevin Gilmore and redrawn by Linear.