your problem is due to IRF 840, MJE 350. Because IRF 840 dead, will Mje overwork-it's very hot, so hot when Mje voltage begins to descend.
So you need to immediately MJE 840 and 350.
thanks
As I reported some instability some time back, I today set myself to some part changes.
I changed the pot, I changed the set resistor: replacing the MJE had success.
With a new MJE350 it worked well, flat on 2 mV/cm. For a little time.
because . . . when I changed the voltage (200 ohms multiturn potmeter; 2SK170GR/110K) then all at once the problem stated a bit again: now there is again a little bit of instability around 10 mV peakpeak.
Is my conclusion right that the MJE350 cannot stand tweaking the voltage [even though it is a few volts to the turn)?
I now have a 12V BE zener; maybe 4V1 is better (the max Vbe being 5 V)? I'm afraid I fried another MJE already. NOW - - I'm chicken.
I changed the pot, I changed the set resistor: replacing the MJE had success.
With a new MJE350 it worked well, flat on 2 mV/cm. For a little time.
because . . . when I changed the voltage (200 ohms multiturn potmeter; 2SK170GR/110K) then all at once the problem stated a bit again: now there is again a little bit of instability around 10 mV peakpeak.
Is my conclusion right that the MJE350 cannot stand tweaking the voltage [even though it is a few volts to the turn)?
I now have a 12V BE zener; maybe 4V1 is better (the max Vbe being 5 V)? I'm afraid I fried another MJE already. NOW - - I'm chicken.
Erratum.
While I was away for over half an hour it has settled again, though there is a very mild drift of +/- 2 mV, now it is stable in time. No jolts.
The output voltage went up from 200V to 203 in the mean time, that is of probably the 2SK170 doing its own figuring out how to respond to the warming up of the earth.
Like it is it can be used in a preamp again.
(I tested with a lab supply 220V-240V, 750 ohms source resistor, that is a good setting to take the current limit out of the test.)
albert
While I was away for over half an hour it has settled again, though there is a very mild drift of +/- 2 mV, now it is stable in time. No jolts.
The output voltage went up from 200V to 203 in the mean time, that is of probably the 2SK170 doing its own figuring out how to respond to the warming up of the earth.
Like it is it can be used in a preamp again.
(I tested with a lab supply 220V-240V, 750 ohms source resistor, that is a good setting to take the current limit out of the test.)
albert
Salas,
I have both 170 replaced, but sorry to let you know they're still the same. It drifts very minor at start and I almost can tune to my desired voltage, then it drifts the way up to the supply voltage 217v. I even tried to tune it back down to 145v, then suddenly the voltage free fall to around 41.5v and stop.
I also have the 2 zeners at 9610 replaced, but won't help. I took the 9610 out from the board and checked them with the new one. The readings seemed normal.
Albert
My mind went to the tiny trimmer wiper now. Maybe a resistor in trimmer's place after you check the set value?
Better use a resistor instead of your trimmer for making sure too? Weird behavior when you tweaked it at a point.
The idea did go over my mind once, but I gave up the thought for the reason that both channels with this symptoms the same time. I checked the temperature on the 170 with a laser gun. It showed almost 40c at the flat surface. The R4 100k 2w is rather hot at 60c and kind of close to the 170. Don't know if the R4 reflects the heat to the 170 or..............other reasons. Is R4 supposed to be this hot.
Very P2P.
Agree to this weirdness (I can't stand things I don't understand
)I changed the trimmer 500 ohms (NOS) to new Bourns 200 ohms multiturn but that was no solution; replacing the MJE350 gave the improvement (that went away a bit later again).
My high voltage supplies are in the lab supply just 16uF/L/6uF/4uF and in my RIAA preamp it is 4 uF/L/30uF. Could it be these race from 250V DC to zero faster than the reference capacitor bleeds down? (But then, I have now installed a zener over there, of which the reverse diode is very effective in protecting the MJE350 B-E junction.)
So I did touch the SK170 (experiment somewhat like Albertli did): immediately the voltage drifted a bit. It went down tens of mV (on the scope it drifted).
If thermal responsiveness of the 2SK170 is a cause, I can check it with a 2SK30, which is known precisely for that good point: no or little thermal drift. (I choose that jFET for my lab supply for that reason .. even though the 2SK170 has a lower noise).
The output behaviour itself is quite acceptable now, just I know that this type of noise is transmitted to an output quite quickly (standard anode loaded triodes have low PSRR), while 50 Hz hum goes rather undetected, these DC-shifts can be experienced more.
albert
Albert & Albert:
So the pots are good.
40C on the K170 is high to be self produced in that bias it uses. It should be radiated from a nearby object. Either a more indifferent fet or some way to protect it from varying heat. A 5W R4. I have experience with 2SK30ATM, problem is in this app it should not have more than 0.6V VGS(OFF) so the under 1mA IDSS ones from a bag should be used. You may need higher Rvref to reach previous Vo. Its noise figure is low, but at very high impedance. We still give it ~100K here so it should be quiet. A low side IDSS BF245A is a good option too.
So the pots are good.
40C on the K170 is high to be self produced in that bias it uses. It should be radiated from a nearby object. Either a more indifferent fet or some way to protect it from varying heat. A 5W R4. I have experience with 2SK30ATM, problem is in this app it should not have more than 0.6V VGS(OFF) so the under 1mA IDSS ones from a bag should be used. You may need higher Rvref to reach previous Vo. Its noise figure is low, but at very high impedance. We still give it ~100K here so it should be quiet. A low side IDSS BF245A is a good option too.
I've been looking lately at the 2SK246 too; this is very linear at low voltages (better at a lower Vds at low Id than both 2SK30 and 2SK170).
The other trick could be to hide the main jFET with a cascode. It makes the jFET more temperature stable and might have an improvement too of the input capacitance of the gate. [In fact, a cascode is what I used a tube for in my HV supply]. I would still call this simplistic, as the main error amp is the MJE350/powerFET.
I'll try this asap
The other trick could be to hide the main jFET with a cascode. It makes the jFET more temperature stable and might have an improvement too of the input capacitance of the gate. [In fact, a cascode is what I used a tube for in my HV supply]. I would still call this simplistic, as the main error amp is the MJE350/powerFET.
I'll try this asap
Sorry for that, won't even try it...
After very good results with SSLV1.0 to power a Tripath, I am trying to run now my first SSHV2, but after several attempts, still no success. I have burned some zeners, one KSA1381 and three DN2540 yet.
Now I have only one DN2554 healty and miss another one to continue amusing this way.
My cuestion, do is possible to place as Q1 or Q2, IRF9610 ?
Input voltage is 310v and output should be 225v/60mA.
Thanks in advanced.
Now I have only one DN2554 healty and miss another one to continue amusing this way.
My cuestion, do is possible to place as Q1 or Q2, IRF9610 ?
Input voltage is 310v and output should be 225v/60mA.
Thanks in advanced.
On pic attached I hope it appears the circuitery on rectification stage. Yellow marker are components deleated, and blue color marker is 4k7 resistor value I changed to raise up the voltage (now I see that's wrong) There is 320v on secondaries, then CRC 100uF/4k7/100uf after modification.
This powers a pair ECC81, on a buffer stage, eating 225v./60mA.
I placed a dummy load resistor: 13k7/8w.
And expect to fix 800mV. on TP but never got start the module.
This powers a pair ECC81, on a buffer stage, eating 225v./60mA.
I placed a dummy load resistor: 13k7/8w.
And expect to fix 800mV. on TP but never got start the module.