JoaMat

Thanks simmconn. I think you are absolutely right about that trimmer. When working with my version of CFA3 I added a small trimmer to the lower current source (sink) to be able to, as you put it, balance the P and N arms of the input stage. I don’t remember my reasons to omit the 10K trimmer. But I made some simulations now in LTspice and they indicate that the trimmer changes the voltage cross 100K resistors with 0.1mV or so (but that is my simulations).

I’m not sure of the purpose of the 10K trimmer. The two op amps control the outputs very well so I think you can set the trimmer to any position without noticing much. Anyhow, I omitted the trimmer along with the 10K resistor connected to trimmer center pin in my CFA3_something project.

Maybe one can feed heater direct from the Traco? A small test showed that current starts at 4.2A, decreases below 3A in 2 – 3 seconds and below 1.5A after another 3 - 4 seconds. Tested both a EML 20B-V4 and a 300B. From Traco datasheet: Output Current Limitation 120 - 200% of Iout max. 145% typ. of Iout max.

Happy Birthday!

I think 2sa1627 will work. Someone have to test it. Let us know how it turns out.

but you have connected negative traces to trim pin on layout above... or am I just confused?

TTP15 pin 3 seems to be a trim pin. Can that pin be used for -Vout?

Happy Birthday!

Happy Birthday!

Happy Birthday!

Happy Birthday!

Joint venture. CIA and Poland.

Well, it’s almost 10 years ago I made the “original layouts”. Just found another version of a layout on my computer from that time. A part of it shows (in ugly yellow circle) a RES90 resistor with text "Resistor I=1,3mA". There is also room for three standing resistors instead of one power resistor.

Who is the producer?

R11 determines the current through LT1021-10 which needs 1.1 mA at 25 degree C. Choose R11 value accordingly. For +/-500V sections; R11 = 400K gives 1.4mA and 0.8W.

Jolly good work! Thank you for the excellent PDF document. Lots of interesting stuff there.

Happy Birthday!

Happy Birthday!

I think you can say the last stage of mini T2 is Q8/V3 and Q9/V4. The signals come via R11 and R12 to base Q8 and base Q9.

Happy Birthday!

Happy Birthday!

I don’t think mini T2 works the way you think, micon21. Here is an excellent description how to build the original Blue Hawaii. There is also a nice explanation how it works. Mini T2 works mainly as the Blue Hawaii does. Read the article (I read it several times – have slow brain) and I think you will get a better understanding how the dots are connected. Good luck and keep on with your good work.

R43,44 are the feedback resistors and R7,8 are the lower tube cathode resistors. LTspice simulation indicates that they all determine the gain of the amplifier. 100K and 100R, as in the original schematics, gives a gain of roughly 1000. With 270K and 2K resistors LTspice indicates a gain of 140. The resistor changes you have done will not change DC voltages at the small tube pins. Maybe your trouble is somewhere else than at the feedback and cathode resistors. But don’t give. It seems you are more than competent to build a mini T2 and, even more important, to fix it if it’s broken. I guess you will have a fully working mini T2 sooner than you now think.

If +220V out from PSU you should have +200V on pin1 and 6 and +69V on pin 2 and 7 upper small tube. Lower small tube should have +71V on pin 1 and 6. Your -334V on EL34 Pin 8 seems to be too high, I would expect something like -400V or lower. This, of course, is in a perfect world. What supply voltages do you read on the amplifier board?

Thanks a lot, guys! I’ve had a terrific and quiet Birthday time with my wife and eldest grandchild - after a "hectic" Christmas celebration with our two children and their families with a half dozen grandchildren.