JoaMat

Hum/noise disappeared after an hour. I’m a bit surprised but I can’t hear it any longer.

Think I prefer stereo. Moved the 300B to a T2. Left channel has EL61 with adapters from China and right side has 300B with homemade adapters. Works all right.

Happy Easter folks! Three months ago I bought a pair of Russian 300B. Intention was to try them in an electrostatic amplifier. Eventually I’ve put them in my DHT mini T2. Only mono version but it works. There is some unwanted hum/noise. Maybe because 5VAC for filament. I’ve DC alternatives, so future will tell if that might solve the issue. Anyhow, I’m enjoying the music (only left ear) and I still have some good stuff left.

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.