Mosfet Identification Help Request

[J M Fahey]

Good, we *still* need to know what you want to do. []
As in: "I need a screen voltage: 400V@30mA max; my B+ is 500V" or whatever. []
And: "I need it to be fixed/I need it to follow B+ to have some sag"

[bob p]

Thanks for the help, guys.

If this circuit design is old and antiquated, it would be hard for me to tell, as I know more about tubes than solid state devices. My education is firmly planted in 1950s technology, not 21st century engineering courses. If there's a better way to perform the required task with a lower parts count and more modern devices, then there's every reason to use a modern circuit instead. The problem is that this is so far out of my comfort zone that its not funny. I just thought I'd build this circuit, not knowing any better. If there's a better way to skin the cat, I'm willing but ignorant.

[Enzo]

We were talking not long ago about high voltage regulators. Seems to me it might have been someone trying to invent a 48v phantom supply, but the LM317 he was wanting to use wasn;t up to the voltage levels... or something. I recall finding some newer adjustable regulator IC that was good for high voltage, but I don't recall just how hugh a V, nor the part number. In any case, the circuits posted above look more or less like the internal circuit of some Vreg IC anyway. WHy build discrete when they already package it in a TO220?

[J M Fahey]

Hi bob-p

it looks like a mosfet is being used with an op-amp in a "voltage stabilizer" type circuit.

Yes, you are right.

Looking at the diagram, the discrete semiconductors seem to be drawn as depletion mode MOSFETS. The problem though, is that when I've been looking up the parts numbers, the only parts I've found with suffixes that match these items are not depletion mode mosfets. In the case of the 2N6761 the Fairchild spec sheets list it as an enhancement mode device.

They are enhancement types.
The symbol drawn indicates so by not showing an internal diode getting into (or out of) the gate symbol (because there's none there); the parallel gate line showing it's insulated from the channel (by a thin glass layer) and the channel drawn with an interrupted line, meaning the "natural" state is open.
The schematic is quite dated/venerable/obsolete/vintage, take your pick, even in the way it's drawn, maybe that confuses you.

the proper supplier/part number for the semiconductors listed in the voltage stabilizer circuits shown below? So far I've determined that the OP176 is an obsolete product by Analog Devices. Its been replaced by the OP184. I've had no luck ID'ing Q8 (6761) or Q9 (8401).

Probably any good op Amp (think TL071) will work there.
I've found the 2N6761 to be a 4,5A 450 or 500V device, quite obsolete by the way.
2N6761 Datasheet pdf - N-Channel Power MOSFETs/ 4.5A/ 450V/500V - Fairchild Semiconductor
I'm sure an IRFP450 will replace it nicely.
Too sleepy (it's 04:50 here now) to follow 2N8401, although i'm sure I'll find it in my ooooollllddd D.A.T.A. handbook rather than on the net. (yep, it's *that* old).
If you found its datasheet, post it here.
These supplies or regulators are very old, needlessly complicated, and they look like the stuff used by the NASA or Vietnam era planes, probably worth U$24.000 each , meaning "taxpayer dollars" and "1968 dollars", not joking about that.
What do you need to be done exactly? (As in Volts in->Volts out @ so many milliAmperes)
It can be done today with *very* simple circuits, although they'll have an error of, say, 500mV , for less than 10 bucks each.

[bob p]

I've been perusing schematics lately, with a particular interest on power supply circuits that use solid state devices in support of hollow state applications.

Here''s an example: the schematic below shows a snippet of two voltage regulation circuits that are used for the B+ and bias supplies. In each case, it looks like a mosfet is being used with an op-amp in a "voltage stabilizer" type circuit.

Looking at the diagram, the discrete semiconductors seem to be drawn as depletion mode MOSFETS. The problem though, is that when I've been looking up the parts numbers, the only parts I've found with suffixes that match these items are not depletion mode mosfets. In the case of the 2N6761 the Fairchild spec sheets list it as an enhancement mode device.

Obviously, I'm making a mistake somewhere. Can anyone help me to determine the proper supplier/part number for the semiconductors listed in the voltage stabilizer circuits shown below? So far I've determined that the OP176 is an obsolete product by Analog Devices. Its been replaced by the OP184. I've had no luck ID'ing Q8 (6761) or Q9 (8401).

Any help would be appreciated. TIA.