Mosfet Identification Help Request

[bob p]

Sorry, I didn't mean to cheat you. Those pages that I linked to were not from the company site. The company doesn't share their schematics. Those pages were from a fan site that is maintained independently. Offhand, I don't know who the site's owner is. I found the interview by Googling for the designer's name.

If I took your comments about obsolete discrete semis and mistook them to refer to an obsoleted circuit design, that was my mistake. I agree that modern semiconductors would be a better choice. If its possible to find modern substitutes for both the 6761 and the 8401 that would make the PSU circuit build-able. I guess this thread will stay open until I have the definitive list of replacements for all of the obsoleted parts, or an encapsulated solution to replace them.

WRT hunting and buying an original one -- most of those devices in working order are selling in the area of $1000. Dead ones still command a ridiculously high price, because most buyers aren't aware of the problems in repairing a PSU board that's based on obsolete components that can't be sourced. Both working and non-working units command prices that are too high and there aren't any "deals" out there.

That brings us to the prospect of a DIY build. The audio signal path is a damned simple circuit that just about anyone here should be able to build. In the best case scenario a well built DIY might sound similar to the $1000 used gear. In the worst case scenario a well built DIY will sound like vintage audio from the golden age. Its not that hard to build circuits that are on-par with the 1950s products, so if the recommendation is to buy "golden era" amps, to me that's equivalent to a DIY recommendation. To me, DIY seems like a no-loose proposition. Its a worthwhile as an experiment, anyway.

Thanks for your helpful posts.

[J M Fahey]

most of those devices in working order are selling in the area of $1000.

All I can say is OUCH !!!
No offense taken and wish you good luck with your project.
Still think that the "mechanical" part will be a PITA, if you want to keep it on the same high level as the electronics proper part.

[bob p]

Look at the end of this thread: http://music-electronics-forum.com/t15120/

I had found the TL783 which takes up to 125v directly
http://focus.ti.com/lit/ds/symlink/tl783.pdf

And Tedmich found several interesting resources. All potentially helpful to you

Thanks Enzo! It looks like the TL783 circuit would have a lower parts count, and my needs fall right in the range of its specs:

Vi - Vo = 125V
Io = 15 to 700 mA
Tj = 0 - 125 C

Best of all: $2.02 shipped from Digikey.

[bob p]

Well, the problem isn't solved yet ... I have been digging but I can't find any suitable integrated solutions for high negative voltage regulation. I've even spoken to Tech Support at TI and they're unable to help.

It looks like I could be headed back toward mosfets/opamps in voltage stabilizer circuits.

can anyone provide specs for the 6761 and the 8401?

[Enzo]

What if you had a 9v battery circuit, and you wanted to add a -9v circuit to it. WOuld you look for a -9v battery?

A negative regulator doesn't need to be made for that job. DO you have a independent transformer winding for your negative supply? If you make a basic supply and regulate it, at the end you wind up with a + and - lead. Usually we ground the - lead and have +V. But if the transformer is not already grounded, you can just as easily ground the + lead and have -V. Still using a positive regulator IC.

As to specs, this is just a power supply voltage regulator, no distortion or freq response to think about. WHat is the raw voltage you are starting with? Your +v knocks 240v down to 180v which would seem like 60v. But when power is first applied, empty caps can seeem like a momentary short, and that is zero volts, so I would want the MOSFET to have at least the 240v rating. SOmeone else may disagree. Looks like your -V starts with the same 240v. And then current. Well, how much current does the circuit need? What is three of four times that much? Pretty much any similar type transistor that meets the minimal specs should work.