JoaMat

@@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.

I’ve two PSUs for my electrostatic amplifiers. The DIY T2 has 500 volts rails so I’m feeding all my amplifiers with 500 volts. Now I’ve been thinking of building a new PSU with 400 volts. From what I understand the only reason to go higher then 400 volts is if you really want high sound levels. Today I’ve brought down the T2 PSU to +/- 400 V and -460 V (the -560 V in my PSU is produced by its own regulator connected to ground). The only modification on T2 amplifier needed was to change the battery voltage from 740 V to 640 V – swapped the 4.7K resistors to 6.8K. Since I use offset servos similar to the opto servo Kevin introduced in his designs a couple of years ago I didn’t have to change anything else.

I’ve been using Denon SC-7000Z for several years and I would say it’s a great tool. With 1.5 mm tip it’s easy to remove a 5 terminal block or a small teflon tube socket. It can also be used as an “hot air gun” and then it’s very practical for desoldering surface mounted components. If interested check Howard Electronic Instruments – I buy spare parts from them.

Two different types of EL34 in there?

Electrokit is my favorite supplier – a small and friendly company. Just takes my 15 minutes by car.

Happy Birthday!

Below is from my kitchen today. I had to test if the DN2540 would do. 25 mA on the meter and voltage, from an old KGSSHV supply, is 887 volts. Only one half of Circlotron and the current seems to stable enough. Might be continued if I don’t break arms and legs during coming week down hill skiing.

My idea with DN2540 instead of “120R resistor” is that you might have better control of the current in the Circlotron. Under normal condition you probably don’t need heat sink with DN2540. 100 V offset should never happen with a good driver but that is in a perfect world. Anyhow, worst case is an offset of +450 V and then the DN2540 is reaching or exceeding its maximum both voltage and power. But I could be all wrong about this.

Average temp of 26.7C - can't be better.

I’ve replaced 120R and optocoupler circuit with a DN2540 circuit. In LTspice it seems to work. If input offset is +100V then I get a current in the Circlotron of 850 mA with the optocoupler and 75 W at 120R resistor and 750 W at the MosFet. With DN2540 the current stays at 25 mA and DN2540 will take some 2.7 W and hopefully nothing will blow. This is of course in theory and what will happen in real life is a completely different story.

What if lower device as DN2540 with C2M1000170D to control current in the Circlotron?

Two months have elapsed. The modifications work alright. Almost forgot what I’ve done. Schematic below shows the difference between the servos.

Of course offset servo is not needed with the Blue Hawaii. Blue Hawaii has been around for a long time. Manufactured and sold by HeadAmp Audio Electronics to many satisfied customers. Been given highest possible remarks by professional tester. As DIYer I do feel entitled to do any modifications to any amplifier I like. Doing so with a Blue Hawaii feels like a privilege. I’m very grateful for the Blue Hawaii and can’t thank you the designer enough.

I’ve used a couple of different offset servos with a Blue Hawaii. I found them very useful. If you like 45 volts drift you should avoid all kind of servos.

Nothing wrong with Servo 2 - the only servo you need.