Simplistic MosFET HV Shunt Regs

[asdiasx]

Example....

I found an example... as I said, the concern is related to the transformers specifications....

 

[king4joy]

I have bought a SSHV2 kit from TeaBag a while ago, but only have time to finish it recently, awaiting testing.

The SSHV2 will be used in my SET line amp with a pair of VT-25A. Each VT-25A is loaded with a CCS (C4S) setted at 12.5 mA.

The original PSU is as attached.
Do I need to modify the PSU for the best performace??

My worry is, the chokes are only rated at 40mA each and I need to set the T.P. to 45mA (12.5 + 12.5 + 20). Do I need to parallel the two chokes??

I plan to set the out-put of the SSHV2 at 270V for the amp....

Any suggestions/recommendations will be welcome.

Thankyou and cheers,

KIng

 

[Salas]

Yes you will need to parallel them so they can handle the 45mA constant current asked by the regulator they will now have to feed. This will also allow for less voltage drop across the pre-filtering. Your minimum input for good 270V output from SSHV2 should be 280V input. 290V is recommended to allow for mains play. Still if you know it will never give less than 280V DC to the reg in your area, then its enough. The tube rectifier needs to allow at more current now also.

 

[king4joy]

Thankyou Salas....so I should move the second choke to parallel the first one...and still keeping all the caps....and I will try for a 290V by adjusting the value of the resistor...thankyou again...

 

[king4joy]

Forgot to mention, the original box does not have enough space for more chokes....I am stuck with the part count....

 

[Salas]

If you can have your last 22uF cap nearest to reg's input its good, it decouples the inductance along the road. What you already have is pretty nice for keeping as rectification and passive filtering to the reg. Helps.

 

[Salas]

P.S. Good luck, I wish success. Post us a photo of the finished system when all is done, and let us know if you liked the passive as is or with the reg better.

 

[Salas]

Hi Salas, sorry it wasn't clear... Let me try to explain graphically:


(home AC outlet 120V)=======(1st Trafo pri120V/sec220V)==========(2nd Trafo pri120+120V/sec12V)============(Ac output 240V)


120V ==================== PRI // SEC ===================== SEC // PRI ============================ 240V to rectifier/regulator


My concern (if it is possible) is to specify the trafo secondary current, so I can get enough current at the output....

Regards

Your primaries current ability should not change if you use them back or forth. So it should be what it was given by the manufacturers as primary max mA. I am very basic in transformer tricks knowledge, maybe I am wrong.

 

[king4joy]

The SSHV2 board is just next to the 22uF....

is it OK if I move the second choke to parallel with the first input choke....and leave the rest the same (the PSU will become a LC type)...

But the board is about 12" away from the CCS's for tubes, and I hope it will work out fine.

 

[king4joy]

Yes, I will post photos when it is finished....

 

[king4joy]

What would be the best way to fine adjust the PSU to get 290V for the SSHV2 board please??

 

[Salas]

Load your PSU's output (disconnect preamp) with resistor that asks 45mA at 290V and tune until you get about 290V I think. 22K//18K//18K 10W each. Then disconnect them and it will give the same if you connect SSHV2 set at 45mA.

 

[king4joy]

22K//18K//18K 10W each.....parallel with the bleeder resistor to adjust for 290V out??

 

[Salas]

No, across output capacitors to the right.

 

[Salas]

Those will be just dummy load so you will be able to adjust your bleeder, see how much the rectifier sags, see your series drop on the chokes. And to try for 280V-290V.

 

[Salas]

Or you simulate on PSUDII. http://www.duncanamps.com/psud2/index.html

 

[king4joy]

OK...ok...understand....put a dummy load that will draw about 45mA at 290V....and adjust the value of the bleeder resistor to give 290V at the dummy....

 

[king4joy]

interesting....after moving out the second choke....the bleeder looks like a load resistor....yes??

 

[king4joy]

so I will use a 6.4K 10W as load; and adjust bleeder to give 290V...then remove the 6.4K, and connect the PSU to the SSHV2.....and I use a 11.6K as a dummy at the output of the SSHV2....

 

[Salas]

10W will melt, 290V*0.045A=13W. That is why I suggested 22K//18K//18K 10W each. You need about 2 times the dissipated power in nominal resistor power to get very hot and 3 times to get rather comfortably hot. Your bleeder is now direct part of the load after the chokes move, yes. The other things you wrote are correct.