Simplistic Mosfet HV Shunt Regs - Page 61

andRookie · 21st October 2009, 12:36 AM

Seems to be ok in test. Acted as you said, the voltage dropped a bit at first.
I have a 10K test-resistor. At 180V this gives me like 18mA trough it and 18mA shunt as I followed Salas scheme (p.53), I guess.

What I have calculated wrong is the input voltage. I thought it would come out 215V but ut is now 240V with the reg attached. I might be running the LEDs a little too hard. Should I adjust the LED-ground - resistor?

Salas · 21st October 2009, 12:47 AM

Just run a bit more current, will be better for the reg and it will sag the trafo a bit. You have quite a sink there, so no problem. Change to a 47 Ohm R1 for about 42mA. The question is if your choke will saturate. How large in VA the TX is and what is its nominal secondary? I don't think you run em hard. What current you derive if you divide the voltage across their resistor to ground by its value?

P.S. You were about to run 2 regs? Then they will sag the secondary for sure. Still 70V is nice for driving faster rise time.

andRookie · 21st October 2009, 01:10 AM

tx is 100mA, have multiple sec on 180, 200, 220. (do not remember which one I use)
Valve rectifier
First cap is 12uF
Filter choke is 50mA, 700R
second cap is a 100uF

I need to cut the heatsink to fit it. Now I think no more than 35C.

234,4v/ 47k = 5mA - how does that sound?

Salas · 21st October 2009, 01:14 AM

Spot on led current I wanted. Also your CCS current looks spot on. Its the leds are really 1.7V it seems. You brobably use the 200V one and your tube rectifier drops 40V. With just a few more mA in the shunt you probably going to make the rectifier duck a bit. Which double diode valve you use? Is it a stiff or limp one for voltage sag?

andRookie · 21st October 2009, 01:24 AM

It`s a 5z4g and I like the looks

The LEDs are red, thats what I`m sure of.

Salas · 21st October 2009, 01:35 AM

OK thought of the solution. R1 = 47R 1W. First cap 6u8 to 8u2. In spec for longevity, plus it will drop some voltage. It does not seem to be losing much before you ask for 100mA at voltages you use. Is it a Brimar?

andRookie · 21st October 2009, 09:41 AM

Yes its a Brimar.
Can use 6uF (it is now 2x6u very large WW2 pio sprague). I`ll play around with the psu.
If I paralell the R1/56E with 293E I get 46,988E. Need to dig deep in my drawer and see what values pops up.

Salas · 21st October 2009, 09:52 AM

Ballpark 40-50R will be adequate. It isn't that critical. Just see you don't go over 55c with your final sink, so to have it working reliably for long. The first CLC cap value is going to help you tune your input voltage. Aim for 50V Vdiff in out reg. You will use one shunt for 2 12+12ma bias asking channels?

andRookie · 21st October 2009, 10:10 AM

One shunt for two channels, yes.

I have one more print and next time I might expand to using two shunts for this preamp, but as for now one will do.

Salas · 21st October 2009, 10:12 AM

Ok. Let us know your impressions soon. And remember, we always like to see nice pictures posted when glowing valves are involved. Good luck!

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21st October 2009, 12:47 AM	#602
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Just run a bit more current, will be better for the reg and it will sag the trafo a bit. You have quite a sink there, so no problem. Change to a 47 Ohm R1 for about 42mA. The question is if your choke will saturate. How large in VA the TX is and what is its nominal secondary? I don't think you run em hard. What current you derive if you divide the voltage across their resistor to ground by its value? P.S. You were about to run 2 regs? Then they will sag the secondary for sure. Still 70V is nice for driving faster rise time.

21st October 2009, 01:10 AM	#603
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	tx is 100mA, have multiple sec on 180, 200, 220. (do not remember which one I use) Valve rectifier First cap is 12uF Filter choke is 50mA, 700R second cap is a 100uF I need to cut the heatsink to fit it. Now I think no more than 35C. 234,4v/ 47k = 5mA - how does that sound?

21st October 2009, 01:14 AM	#604
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Spot on led current I wanted. Also your CCS current looks spot on. Its the leds are really 1.7V it seems. You brobably use the 200V one and your tube rectifier drops 40V. With just a few more mA in the shunt you probably going to make the rectifier duck a bit. Which double diode valve you use? Is it a stiff or limp one for voltage sag?

21st October 2009, 01:24 AM	#605
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	It`s a 5z4g and I like the looks The LEDs are red, thats what I`m sure of.

21st October 2009, 09:41 AM	#607
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	Yes its a Brimar. Can use 6uF (it is now 2x6u very large WW2 pio sprague). I`ll play around with the psu. If I paralell the R1/56E with 293E I get 46,988E. Need to dig deep in my drawer and see what values pops up.

21st October 2009, 09:52 AM	#608
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Ballpark 40-50R will be adequate. It isn't that critical. Just see you don't go over 55c with your final sink, so to have it working reliably for long. The first CLC cap value is going to help you tune your input voltage. Aim for 50V Vdiff in out reg. You will use one shunt for 2 12+12ma bias asking channels?

21st October 2009, 10:10 AM	#609
andRookie diyAudio Member Join Date: Apr 2006 Location: up north	One shunt for two channels, yes. I have one more print and next time I might expand to using two shunts for this preamp, but as for now one will do.

21st October 2009, 10:12 AM	#610
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Ok. Let us know your impressions soon. And remember, we always like to see nice pictures posted when glowing valves are involved. Good luck!