Help with creating a simple tube HV regulated supply

[jmillerdoc]

I was wondering if anybody had a fairly simple schematic to design a tube regulated HV supply for 300v for a preamp I want to build. Is it Kosher to put a tube regulator after a CLC filter? I want almost no ripple when it is all said and done. This will obviously be my first attempt a a regulated HV supply, I have always wanted to try one but really don't have the first clue of where to start. I have seen several schematics out there but none creating 300v so I haven't been able to just copy one to date. I want to keep this as simple as possible.
Thanks for your help in advance, you guys always come through here!
Jeff

[SpreadSpectrum]

Jeff,

I have an HP650A sine wave generator that has a simple tube regulated supply. You should be able to find a schematic easily on the internet. It is adjustable through a resistor divider.

Heath

[chrish]

Does the regulator have to be tube? Maida style regulator can be made with LM317 voltage regulator. If tube is requirement, found this with a google search, might be useful - Regulated HV power supply

[astouffer]

This was scanned from an issue of Sound Practices. The tube is a 6BM8 although you could probably sub in something similar without too many problems.

[bob91343]

Make life easy and use VR tubes. You need 300 Volts? Use a pair of 0A2 in series, or a pair of VR150s. As long as you have enough striking voltage available, this makes for an extremely simple yet effective regulator.

[chrish]

Originally Posted by bob91343

Make life easy and use VR tubes. You need 300 Volts? Use a pair of 0A2 in series, or a pair of VR150s. As long as you have enough striking voltage available, this makes for an extremely simple yet effective regulator.

Good reference for VR circuits. Basic VR Tube Regulator Circuit

[jmillerdoc]

Originally Posted by bob91343

Make life easy and use VR tubes. You need 300 Volts? Use a pair of 0A2 in series, or a pair of VR150s. As long as you have enough striking voltage available, this makes for an extremely simple yet effective regulator.

How much striking voltage is required for a Vmax of 300-325V?
Jeff

[duderduderini]

Hi.
I have used this design successfully for 3 of my preamps. Yes I use a clc filter prior to it and its good for 100mA. It is not my design and the schematic is annotated to its rightful designer.
Hope it works for you.
ps this design was available on a chinese based web site so I assume that its cool to post it. My apologies if it isnt. It was a list of mods to the lsdy regulated voltage kit addressing a few of it shortcomings.

[jmillerdoc]

Originally Posted by bob91343

Make life easy and use VR tubes. You need 300 Volts? Use a pair of 0A2 in series, or a pair of VR150s. As long as you have enough striking voltage available, this makes for an extremely simple yet effective regulator.

OK, I did a little research on the OD3 and OA2 VR150 type tubes. I never knew much about these things until now. Very interesting device, the NEETS module does a pretty good job of explaining how they work.

A couple of questions though, you say to use 2 of these in series....so would my final B+ come from the cathode of the 2nd tube in series?

The NJ7P database shows the Vmax supply voltage to be 185v for both of these tubes. To get the 300V I need the first tube in series would see 300v thus exceeding the specs. I am not sure how this works really though. Wouldn't the first VR tube in the series limit the voltage to 150 seen at the plate of the second tube??? How can 2 of these tubes in series provide the 300V in the end if they are designed to regulate the voltage to 150. Seems to me the finel voltage of two of these in series would be 150V, just "double regulated" now. I don't understand.....please enlighten me. It is not that I don't believe you, I just don't see how this works.
Jeff

Edit:

I just went back and reviewed the NEETs module on VR circuits and not just the VR tube itself. I think I understand now, the series of VR150 tubes is placed across the B+ and ground, in parallel to the load. Thus the VR series of tubes acts like a shunt. My final B+ should be taken from the top (plate) of the first tube in series.....am I correct in this now?

Thanks,
Jeff

[danFrank]

Think of the VR tubes as shunt regulators, kind of how you would employ zener diodes. You totem pole the VR tubes; top end connected to the voltage you are trying to regulate, the bottom to ground. If the supply voltage is too high, then you need to put dropping resistors in series before the voltage supply gets to the VR tubes. Resistance values have to be calculated by what your load current is.
VR tubes can not have much current going through them or you will fry them. If you end up making a simple VR tube only regulator, you have to calculate the current pull of your circuit plus the current that is permissable through the VR tube to find out what series resistance value you need to use in the supply rail.
How many milliamps does your circuit pull? If it's more than maybe 10ma (I'm guessing here; look at the VR tube specs) then consider using a pass tube connected to an error amp (which is connected to the VR tube through its grid).
One more thing Vr tubes like A LITTLE capacitor across them which helps with regulation. Something like .05uf, if I recall.
Hope this answers your questions... Daniel