Simplistic Mosfet HV Shunt Regs - Page 357 - diyAudio
 Simplistic Mosfet HV Shunt Regs
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diyAudio Member

Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
 Originally Posted by Salas Yep it may, but the Supertex one underneath does the current. The IXTP shields HV. (68Kx2)*K117 max in circuit current=Vo max.
Assuming the 2SK117 that's in there now is the component "limiting" the voltage to 340V, I would find it's Idss less than (approximately) 2.5mA?

So I should find one 2.8mA or better? (by your formula)

Gary

 9th December 2012, 10:59 PM #3562 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece 3mA in circuit should go full tilt 400V. They give bit less IDSS than free with a battery when in circuit due to less VDS there, so a 3mA free should suffice.
 9th December 2012, 11:01 PM #3563 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece Another way is 75K 2W resistors instead of 68K if short of JFETs
diyAudio Member

Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
 Originally Posted by Salas Another way is 75K 2W resistors instead of 68K if short of JFETs
Salas,

BTW - I did not yet substitute a 1 ohm for the 10ohm sampling resistor, I do not have a 1% MF.

I found a strong 2SK117 with an Idss of 5.6mA (using the 9V battery test)
However, it did not make so much of a difference.

I can now readily get the output to 350V, at 80mA. However, that's with a minimum of 420V in. If I drop below that, the output falls pretty fast. I think that's a maintainable number (420V) for Vin, since it's coming off of my plate supply, but why would I need 70V overhead to maintain a Vo of 350V??

Very odd, the other board id not behave like that at all!

Last edited by roger57; 9th December 2012 at 11:48 PM.

diyAudio Member

Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
 Originally Posted by Salas Another way is 75K 2W resistors instead of 68K if short of JFETs
OK, I found the problem. Time for a break while I fix my head...

Ok, all better now.

I had 2 resistors in series for the load, a 5K and a 820 ohm. I had my meter clipped across just the 5K.

Next time I'll look a bit closer before I send an SOS.

Sorry to bother you Salas, and thanks for your help.

Gary

 10th December 2012, 04:35 AM #3566 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece No shortage in semis IDSS then, wrong load. Happy end.
 10th December 2012, 06:06 PM #3567 diyAudio Member     Join Date: Sep 2009 Location: Catalonia - Europe Salas could benefit the SSHV2 adding before a cap multiplier?
 10th December 2012, 07:10 PM #3568 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece The multiplier will ruin the flat low Z. Rather not. If you meant putting the mult before, rather yes. But use output cap on the mult to avoid it will ring with CCS.
 10th December 2012, 08:06 PM #3569 diyAudio Member     Join Date: Sep 2009 Location: Catalonia - Europe I ask because as you know I use an AZ1 so PSU can have more than 60uF, could you link me to a schematic or thread where I can get the information?
diyAudio Member

Join Date: Apr 2011
Quote:
 Originally Posted by king4joy Final testing of new PSU with 150K bleeder only. V out = 377V
Salas....I changed the shape of the heat sink and now I am fitting two SSHV2 boards in my PSU box....

I will set each board to about 30mA giving about 8-9mA to each VT25A tube.

If I connect 2 x SSHV2 boards to the PSU instead of one SSHV2, do I need to change the bleeder value or other parts of the PSU??

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