Simplistic mosFET HV Shunt Regs

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#542
Its true I don't know about circuits. Just basic stuff. I am diying simple things, I put them to the listen, and if I feel they work good I show them. But I don't know if they are safe for all scalings or if they inhibit some flaws, beyond what I made for a particular working application. So its there for others to explore further if they fancy. No claims.
 
#544
I put you MJE350 not to need, difficult to find fast, sink for small MPSA TO92. MJE can take small heat by itself. More stable maybe. But if you have only MPSA92 you can still use it.
 

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#545
Salas said:
I put you MJE350 not to need, difficult to find fast, sink for small MPSA TO92. MJE can take small heat by itself. More stable maybe. But if you have only MPSA92 you can still use it.
Click to expand...

OK! I m finish my pre whith Salas shunt,
The sound is very good, but there is a litle noise * is eeee*, i dont know why?
I think my pre is not good, I have to check it now!
thank Salas!
pm I use Filter 220uf- 900R- 220uf/450V . After I connect to Salas shunt!
290V. and out put 230V.
 
#546
Measure output of shunt, is there any AC? To know it regulates well. eeee sounds like oscillation. You must use Oscope to find where it is born. Used MJE350? How many Volt across R1 and what R1? Can't go up to 240V? If you have a picture of it and the preamp I would like to see.
 
#553
Hey quang, do you have one shunt regulator feeding both pre channels? How much current does each preamp channel draws?

I think you setup your shunt reg current limit too low. This could explain the voltage so low on the output.

From your measurements it shows that the total current through R1 is 47mA = 2.21V / 47R. Seems a bit low.
 
#555
OK, let's see. You got 47mA total going through. If you are 100% sure that each channel takes 17mA, then 47 - 17 - 17 = 13mA. That is the total current that is left for biasing and shunt mosfet. I think that's too small. Make R1 just a little smaller value and measure everything again. Do you have a resistor around 40 ohm for R1? You could use two 75R in parallel.

Also, insert a 1R or a 0R1 resistor between the source of Q3 and ground, and measure the voltage across it, with the circuit powered.

You're working with high voltage, be careful! I see you don't have a bleeder resistor in your PSU filter. Your caps retain high voltage, so make sure they are discharged when you work on the circuit.
 
#556
ikoflexer said:
OK, let's see. You got 47mA total going through. If you are 100% sure that each channel takes 17mA, then 47 - 17 - 17 = 13mA. That is the total current that is left for biasing and shunt mosfet. I think that's too small. Make R1 just a little smaller value and measure everything again. Do you have a resistor around 40 ohm for R1? You could use two 75R in parallel.

Also, insert a 1R or a 0R1 resistor between the source of Q3 and ground, and measure the voltage across it, with the circuit powered.

You're working with high voltage, be careful! I see you don't have a bleeder resistor in your PSU filter. Your caps retain high voltage, so make sure they are discharged when you work on the circuit.
Click to expand...

Ok! I try to do that!
Thank! let wait for me!
 
#560
Looks a bit better now. I also asked you to insert a 1 ohm or a 0.1 ohm resistor between the source of Q3 and ground, and measure the voltage across it, with the circuit powered. Have you done that?[/QUOTE]

Yes, I do that!
My pre is stil ees ..esss ! * not change*
I do sample you show!
1 ohm or a 0.1 ohm resistor between the source of Q3 and ground,
I use 1R between Q3 to ground and V= 220V.
i think my pre use tube 6c45, Is is noise!
I check my pre!
Thank
 
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