JoaMat

A faulty ksc2690 (2sk216 substitute) north of one of the batteries. It tested alright on transistor tester but at a much lower hFE than specified.

Problem solved. No hum or noise that my old ears can detect.

Thank you. Them pins looks very interesting indeed. Regarding my current project. Goal with it was to build a T2 on an original board with all modern components. After a visit in the ditch I returned to the narrow road. Rebuilt the batteries to original LED version on the board. Had to change some resistors as I reduced voltages - battery is 640V instead of the original 740V. Furthermore the change to fjpf2145 instead of 2sc3675 called for a Darlington par out of pair of fjpf2145 in batteries. Very easy to make a Darington pair on the original board. Yellow Teflon wire from base to a via on the board – perfect and the via has a perfect diameter. Some components (ksa1220, ksc2690,ksc1008 and j112) have different pin out as the original ones so I twisted their legs to fit the board. Thanks Michael (mwl168) for how to bend legs on the ksc1008. Bottom line: I believe I’ve built a decent version of DIY T2 with all modern components. I’m satisfied and am about to make myself not so sober (it’s Friday evening). P.S. some problem with one channel, unwanted noise and hum. Happens now and then if you have T2s…

Nice balance servo. Here is an old T2 board with small boards with HN4C51J replacing 2SC3381. By the way Kerry, what kind of pins do you use with your small daughter boards?

Yes, of course.

No twisting they can't be at same side of the board due to pin layout of c3381.

You use a board without 2sc3381 footprint?

I’ve used mpsw06, big brother to mpsa06. Here in my modified T2 (mpsw06 in red circles). Here in a DIY T2. Both pieces on same side of board and held together by heat shrink tube. Than you have to twist legs so they look like a Dancing Fool. A lot easier just to stick a pair of TO92 from opposite sides. Want surface mount? HN4C51J.

Now I’ve tried them. KSC1008, put them in like this, one from component side and the other from solder side. Save you a lot of money. J112, changed 22K resistor to 13.7K then able to adjust to 6.55V. Doesn’t save you so much money.

Here is a T2 on original DIY T2 board with all modern components. High voltages decreased by 100 V to satisfy fjpf2145 and ksa1156. Batteries are on small daughter boards. There is annoying hum on left channel. Right channel is silent so hopefully it’s possible to get rid of the hum.

I’ve been using 1.6mm/1oz boards for some years now and I believe they are sufficient in most cases. James (jamesmking) has built one mini T2 and I’ve built two with 1.6mm/1oz.

So you have 7.43V with the 10K trimmer at endpoint? What is the voltage cross 22K resistor of the other battery?

Power supply is back. Replaced a number of FQPF8N80C, 30V zeners, 15R power resistors, one 2sa1486 and one 2k resistor. What actually killed the power supple (except the guy that should be feeding ducks) has to be investigated…

Today has been a nice and interesting day. I finished a mini T2 with active battery. The copper color board on right side in picture in previous post. Late afternoon I were ready for the first power on. One DMM to measure one side verses ground and another to measure the other side. High voltage clicked in – no explosion – on side showed a few volts verses ground while the other almost 400 volt verses ground. It took some time for me to realize that the 400 volt reading in fact was the BIAS. I’m getting to old for this. When I found the right measuring points I had very nice readings. Batteries are always interesting. Readings as follow. Left +194V and -443V, right +196and –443V. So they also seem to be alright. (using 640V instead of original 740V) Connecting headphone. Very noticeable hum but the music sounded good. After a while very annoying noise came. The noise almost disappeared when I approached the trimmer with the screwdriver but came back when I pulled back my hand. Turned power off and changed the small tubes, power up again, lower my guard and went for a cup of coffee and… it all exploded… So tomorrow I have to fix the power supply for the second time within a week. On amplifier board visible; burned traces, resistors and one popped transistor. Maybe I should feed ducks.

Kitchen in a terrible mess. The fellow in black is Pepsi and he loved schrimps. RIP.

Thanks, BUL216 added as c3675 substitute candidate. Here is a schematic of latest battery module if interested. R2 sets current through the voltage reference. R2 = 4.7K gives roughly 0.9mA. With 4.7K Q3 is needed if NPN is FJPF2145. If NPN is 2SC3675 Q3 is not needed. If R2 is 2K then roughly 2mA. Then Q3 is not needed for neither 2SC3675 nor FJPF2145. Purpose of R4 and R5 is to determine current through Q9,Q11 and Q10,Q12. With Q3 I measure roughly 0.05mA through both sides. Without Q3 almost all current goes through Q10/Q12 and if not enough the desired voltage can’t be regulated and that is what happens with FJPF2145 while 2SC3675 works but it’s very close…

No, fjpf2145 is not a direct replacement for 2sc3675. 2sc3675 is a 900 V device while fjpf2145 is good for 800 V. I’ve used fjpf2145 in all c3675 positions on T2 except for Q8-10 and Q13-15 (output current sources). But if you decrease to +/-400V I guess you can replace c3675 with fjpf2145 here as well. I’ve also replaced c3675 with other transistors than fjpf2145. For instance Q30,31 with 2sc3324, a sot23 smd part. Might pop up in a future mini T2 with active battery...

There are only a few modern npn alternatives to c3675. One is fjpf2145 which I’ve used since several years. In my modified T2 the fjpf2145 work alright with its batteries. The battery I’m trying now drives c3675 but not fjpf2145 without stn0214 in a Darlington pair. With stn0214 in the battery you can use whatever npn you like c3675, c4686, ksc5026 or fjpf2145. So for time being I don’t consider stp03d200, but it will certainly work.

Just removed stn0214 (the sot-223 device mentioned above). The npn I use on test board is fjpf2145. It has lower hFE than 2sc3675 and battery on test board is not capable to drive the fjpf2145 alone, it needs the Darlington pair. For reference, https://www.head-case.org/forums/topic/6837-the-ultimate-diy-a-stax-srm-t2/?do=findComment&comment=419666 , here Kevin wrote about darlington out of a pair of 2sc4686. I believe hFE for 2sc4686 is even lower than for fjpf2145.

Made a new small board. All components moved to one side and a sot-223 1200V npn added to form a Darlington pair with the big npn in the battery. It’s possible to use it with Kevin’s original DIY T2 board. Remove battery components from main board and solder in the daughter board (three pins, fits right in) if you dare. Myself I’m a bit shaky after last failure.

Thank you. Using a T2 amplifier as a test bench might be… not so smart. Milled this test board today. On heat sinks; 10m90s current sink to the right and high voltage npn to the left. The small board on the left is the battery that killed my T2.

Since there is no "What Are You Destroying Today" thread I post here. Yesterday, while trying a modification to a battery on the T2 that was meant not to be modified in any way I had a "gun shot" when high voltages were applied. I had to replaced three mosfets, two zeners, and one power resistor in PSU. Amplifier needed four c3675, three k216, only one j79 and two leds. Now I’m happy again. Some broken parts in a small cup. RIP.

May I ask - what software did you use to create files for CNC machine?

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