Simplistic MosFET HV Shunt Regs

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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amandarae said:
Hello guys! I need some guidance troubleshooting the SSHV2.

I have followed the test procedure per SSHV2 build to a tee, including testing
and works fine. I only have 120 Vdc supply so I was unable to vary the voltage but the output V is almost the same as the input V.

I then connected the SSHV2 to the circuit (preamp). H+ is 198 Vdc. I can regulate the output B+, set to 150 Vdc (R11), and adjust the current (R4) no problem and the unit was operating smoothly. I waited 25 minutes, not much change so just fine tuning to set the V and I.

I was testing the preamp for about 45 minutes and I did not have a problem with the regulator. I connected two meters the whole time and reads 150 Vdc and 360 mV (36 mA) stable. I then connected I believe is a shorted tube and I heard two "clicks", that sound like a spark but no flash. As a result, B+ =9.3Vdc, but current was still 36 mA (360 mV). I measured H+ input and it was the same (198 Vdc). I immediately shutdown the power.

On the bench, I inspected the board visually. No burnt smell or burnt component I can see. Connected to 10k resistor (S0, F0 and S+, F+), I applied 120Vdc just like how I tested it and expecting about the same at the output. Instead, I have ~ 9.3 Vdc.
Is Q1 and Q2 blown? What is the best way to check it? I was unable to measure voltage from Gnd to bottom or R5.
Thanks!
Abe
Click to expand...

amandarae said:
Made some measurements. H+ at 118Vdc.
Q1: VGate (VG)= 13.287 V, VDrain (VD)= 118 V, VSource (VS)= 11.23 V
Q2: VGate (VG)= 9.185 V, VDrain (VD)= 13.28V, VSource (VS)= 11.23 V

Q2 dead?

Abe
Click to expand...


If you can still adjust CCS mA the input CCS section semiconductors are OK. If not, measure Q1 & Q2's VGS (between pins 1 to 3 each). For healthy ones its usually around 2V in this circuit. When that section works one or more semiconductors had probably blown down the line. Usually the small ones not Q3 which can be confirmed for 3-4V healthy Vgs or not after the smalls ones had been taken care of. In those troubleshooting posts, after the CCS section low voltage test info, there is also some info about checking the voltage regulation shunt section. Read #4491-4498.
 
amandarae

amandarae

Member
Joined 2004
Salas said:
If you can still adjust CCS mA the input CCS section semiconductors are OK. If not, measure Q1 & Q2's VGS (between pins 1 to 3 each). For healthy ones its usually around 2V in this circuit. When that section works one or more semiconductors had probably blown down the line. Usually the small ones not Q3 which can be confirmed for 3-4V healthy Vgs or not after the smalls ones had been taken care of. In those troubleshooting posts, after the CCS section low voltage test info, there is also some info about checking the voltage regulation shunt section. Read #4491-4498.
Click to expand...

Thank you Salas!
I will read the posts, test, and will report back.

Abe
 
TonyTecson

TonyTecson

Member
Joined 2003
amandarae

amandarae

Member
Joined 2004
amandarae

amandarae

Member
Joined 2004
Made some measurements:

Power Off
Red Probe on Emitter
Q4 (E-B) pin 1&3 = 78.3 kOhms; Q5 =0.65 ohms
Q6 Pins 1-2 0.67 ohm, 2-3 2.76 ohms, 1-3 2.35 ohms

Power ON
10 kOhms load; 118V H+ in.
Q1 (1-3) 2.0 V; Q2 (1-3) 2.0 V; Q4 (1-3) 0.64 V; Q5 (1-3) 0.0V

CCS still can be adjusted no problem. VOut=9.18 V

Looks like Q5 is dead?

Abe
 
amandarae

amandarae

Member
Joined 2004
Thank you Salas!
I will follow your instructions. Unfortunately, I do not have a spare Q5 but Mouser is just a few clicks away. I will also source Q6 as it is not readily available. I asked Mike (TeaBag) for the 2SK117 spares and graciously acknowledge that he can sell some.
Thank you and I will report back.
Abe
 
amandarae

amandarae

Member
Joined 2004
Got some time testing and received replacement parts today.
D3 -> shorted; replaced.
Q5 -> dead, same reading as I posted earlier; replaced.
Q4 -> healthy
Q6 -> suspect, same reading in and out of the circuit; replaced.

Power up, success!!! Thank you Salas and the rest who helped me, much appreciated!

Abe
 
A

audiorado

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Joined 2009
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SSHV2 Probem

Hi folks,just buyed from some diyaudio member complete kit for this reg.Iv put al together and it seems something is wrong.Becose the Q3 Irf840 is not get hot,not ewen warm.My input voktage is 175V on output I get 115-131V.I can without problem set the current on ccs withot problem and I can set the voltage on output 115-131V.I have set the current 60mA,so 40mA for the pair of tubes and 20mA spare for ccs.Output voltage is now set to 120V.So if I understund right it must be around 2,4w dessipation on Q3,but the Q3 get not ewen warm not hot can it be it is defective??Plese for help.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
When setting CCS current with no problem then it must run into somewhere. Maybe your load consumes more than you expect and very little goes to the shunt MOSFET (IRF840) so it remains cool. Maybe that is also why you can't go above 131V. Current limiting. The IRF840 must show few Volt of VGS (2-4V between pin 1 and 3) if healthy when few mA run through it and its open.
 
A

audiorado

Member
Joined 2009
Paid Member
Hi Mr.Salas,
.....thanks for your answer.Im using this one piece reg to feed voltage to pair lundahl LL1660 transformers that Im using for triode 71a on preamp output.I have set 120V on Sshv2 reg output with this voltage I become 100V on each anode thru transformer and by -18V bias I have 22mA on each tube.So 22mA per tube is 44mA bouth and 20 mA for ccs itself is 64mA.I have set the ccs without problem to 64mA.The reg itselfs is feed thru ClClC psu with 75uf mkp and pair chokes hammond 20H 100mA.When I mesure the voltage betweeb n pin1 and 2 on irf840 I can read 124V.Like I say before input voltage is 170V.When I mesure the voltage from ground to Drain pin it is 116V,ground to Gate 3.1V and ground to Source is 0V ,on irf840.I have no scope on hand rigjt now so I can only mesure with multimeter.
 
A

audiorado

Member
Joined 2009
Paid Member
Hi Mr Salas,thanks and yes now is working,I set the ccs to 80mA and now the Irf840 get also hot.And the sound thru lundahl is better,but on the end not my cup of tea,I prefer Ales Moglia gyrators with 71a tubes in my system,the sound is much faster,the bass deeper and articulate and the output impedance better for my D class power amps.Thanks for help.😉
 
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