newbie power supply / voltage regulator question

i searched around, but couldn't find this info, if it exists on here, a link would be great.

[backstory]
so anyway, i dug out the green pres i stuffed years ago and decided to try and figure out why they didn't work back then. i no longer have access to a bench PSU, so i am trying to finish the one that a third party started making for me for the green project. the design was pretty similar to peters, but different in some ways.
the +15/-15V rails are done, but the phantom circuit is only as far as the voltage multiplier stuff.. so it's hanging with an unregulated 90V at it's end currently.
[/backstory]

in going through the test process, i noticed my voltages from the power supply are off a little. like +15.2/-14.67V. I'm using an 815 and 915 regulators, respectively.

my first question is, since these are fixed regulators, can i assume that the variance i'm seeing is just their standard tolerance?
second question, how to i remedy this? i could just throw a resistor on the positive rail to knock it down, but i don't know how to make up what i need on the negative rail. do i just order a bunch of replacement regulators and try them all until i get closer?

final question: to finish the 48V rail, i have all the parts except an adjustable 317 regulator. i do have a couple non-adjustable 317s that apparently yeild 37V. would this be acceptable here for testing sake?

thanks, and i apologize for the dumb questions.

Do I just order a bunch of replacement regulators and try them all until I get closer?

Click to expand...

Nop. You simply forget about these voltages--anything between 12 V and 18 V is close enough...

I do have a couple non-adjustable 317s that apparently yield 37 V.

Click to expand...

There are no non-adjustable 317 regulators. If you really have 90 V at the input a 317 will die though--there's recently been a thread about that. I'd call this a bug in the according PSU, others might disagree.

Samuel

[quote author="Samuel Groner"]

Do I just order a bunch of replacement regulators and try them all until I get closer?

Click to expand...

Nop. You simply forget about these voltages--anything between 12 V and 18 V is close enough...

I do have a couple non-adjustable 317s that apparently yield 37 V.

Click to expand...

There are no non-adjustable 317 regulators. If you really have 90 V at the input a 317 will die though--there's recently been a thread about that. I'd call this a bug in the according PSU, others might disagree.

Samuel[/quote]

gotcha. maybe my concern about the 317 was just that it didn't adjust all the way up to 48v, and i confused the issue with something else. (i get confused easily. hehe.)

yeah, I wasn't sure about the 90V, I wondered if maybe the voltage was higher to compensate for something else, but didn't really know. the multiplier has three steps, so i can just tap off the second one, which is 60V.. will check the specs to see if the 317 can deal with that.

thanks for the info!

Tapping off the voltage at the 60v point is the way to go. You might find that your AC voltage from the transformer secondary is a bit high which is why the tripler stage is giving 90v.

Peter

[quote author="peterc"]Tapping off the voltage at the 60v point is the way to go. You might find that your AC voltage from the transformer secondary is a bit high which is why the tripler stage is giving 90v.

Peter[/quote]

cool - thanks peter!

I've used LM317HV regulators for phantom, but they worry me. I think, if you want to be nice and safe, put in a TL783.

Peace,
Paul