Simplistic MosFET HV Shunt Regs

[Salas]

thank you very much .

You are welcome. Another thing I see is 285V and 255V B+ points in your preamp. You could adjust the series resistors following in those RC networks in your schematic for proper voltage drops to use one B+ value common for both points. Its simply about measuring DC drops on those resistors and applying Ohm's law to solve for current.

 

[widi]

You are welcome. Another thing I see is 285V and 255V B+ points in your preamp. You could adjust the series resistors following in those RC networks in your schematic for proper voltage drops to use one B+ value common for both points. Its simply about measuring DC drops on those resistors and applying Ohm's law to solve for current.

Thanks again and I will follow your recommendation.
Another question and I know that is already very disputed.
Can I use this JFET, 2N4393-E3 instead of 2sk117gr, attached datasheet?
If yes what modification do you need?

 

[Salas]

I don't think that you will chance on any lowest range 4393 5mA-7mA IDDS samples with -0.5V to -0.7V Vgs (off) that you need to replace the K117, but even if you will do, their en (nV noise voltage) is 10-15 times higher. No, not recommended. There is the in-production 2SK880GR surface mount direct equivalent that you can use a surface to through hole mini pcb adapter for it like those little platforms they sell on ebay.

 

[widi]

I don't think that you will chance on any lowest range 4393 5mA-7mA IDDS samples with -0.5V to -0.7V Vgs (off) that you need to replace the K117, but even if you will do, their en (nV noise voltage) is 10-15 times higher. No, not recommended. There is the in-production 2SK880GR surface mount direct equivalent that you can use a surface to through hole mini pcb adapter for it like those little platforms they sell on ebay.

Thank you, Mr Salas, I will keep this in mind.
In this same forum I have found an Ebay provider in Germany that you recommend and the transistors are not fake.
thanks for your help

 

[king4joy]

What test ot tests can we do to separate the real ones from the fakes ??

 

[Salas]

What test ot tests can we do to separate the real ones from the fakes ??

Visually there are some clues, technically is about confirming the datasheet by measuring IDSS & Vp for calculating gm unless you got a tracer and a surely original sample to compare full curves. See posts #4916,17,18 in the link: http://www.diyaudio.com/forums/powe...tic-mosfet-hv-shunt-regs-492.html#post4411651

 

[merlin el mago]

Salas LV shunt regulator & CCS test is:

To only short F+ with F0 is enough
Can put 4.7k across each 68k, feed 30V input from lab supply and see if the output can adjust to 22V on 220R dummy. That would be a full LV test. If successful remove the 4.7k resistors and set the reg for its HV duty.

I guess the 220R dummy load is connected between S+ & S0, right?

 

[Salas]

In the CCS only LV test no dummy or sense leads are needed. The F+ & F0 lines have the CCS always across them if you look carefully at the schematic..

 

[merlin el mago]

I want to test the CCS only with LV. What have I to do?

 

[Salas]

See post #4479

 

[merlin el mago]

Thanks, PSU fuse 1,6A gone, I have on hand 2A or 1A wich one can I use?

 

[Salas]

2A

 

[merlin el mago]

Used 2A fuse, CCS works. Red LED don't lit, I go to check the sk117gr & the rest of semis.

 

[Salas]

OK

 

[merlin el mago]

Salas checked all semis, LED and resistors and are ok, still don't regulate voltage and still LED don't lit any suggestion?

 

[Salas]

For the LED to shine and for output voltage to develop, the JFET current must go through it to the the 68K resistors. Maybe the trimmer has a problem or there is discontinuity in some PCB line or a bad solder joint in that path?

 

[merlin el mago]

Thanks Salas I will check.

 

[merlin el mago]

Salas was a cold joint 68K resistor.

I have a question: I changed the 10K anode load resistor for 15k 600 ohms OPT to use as headphone the attached schematic, do you know how to calculate the new B+ value using the opt?

 

[merlin el mago]

With OPT I measure 77,3V just now. Each triode dissipates 10mA.

 

[Salas]

So we nailed it, it was a bad joint.

When you have a target operating point that looks good on the datasheet curves then you can adjust B+ until you reach it.