Pyramid PS-21K voltage mod

[Technotronic]

Recently fixed one of these up, it had a bad bridge diode block. I went and installed
an LED voltage display readout and its operating well, delivering nearly 25A.

I need a supply that will deliver 26V at a low current no more than 100mA,
and also 50V at about 2A max and was curious if a voltage doubler of some sort
could be put in as a mod to double the 13.8v once for the 26V, then again for the 50V?

I have studied some voltage doublers , triplers and quads online but not sure what way to go.

The PS uses half the diode bridge block as a FW center tapped setup, and I wound up ditching that
for 2 stud mount high current diodes that were in my parts bin...in the photo.

I am thinking maybe a DPDT switch of some sort to bring the doublers in and out perhaps.
The 2N3055 transistors are about 60V rated, so they should handle the higher voltage, and perhaps
I will have to upgrade some of the caps...and maybe the op amp board would also need some changes?

Or am I better off building a separate project box to just plug the output jacks into and let it handle all that?

[coromonadalix]

yes and no   

you can hack it  to higher voltage, but half of the current,  but no adjustable current
to have adjustable current its another matter / design etc ... it will add more complexity and costs

you have to remove the xformer center tap,  and change where the main ground supply is / will be

lucky you  the psu  has a floating section for the lm723


but the voltage divider potentiometer need to be recalculated  and a few things too,  you need to get the lm723 datasheet for floating operation and values calculations

in red circle   you have to check theses

but if you have no experiences you may or will fail,   switch and other parts need to have calculations,  and you can not switch   when the psu is powered on

i hacked an ps51k to higher voltage / half current with no problem,  they are all based on the same design / topology

to add digital meters  i added another small psu for them  since for the amps you need isolated supply too, but im on the positive rail, not by the ground as many small meter does

and the thermal switch   was the 1st thing to go out loll

theses a crude / basic psu's     the lm723 can make a good job if you know what you're doing, if not it will get unstable at some point


oh  tweaking the xformer  will get you around 25vac  once filtered will be around 40vdc,  you will not be able to get more,  maybe around 35vdc out of the psu

forget your 50v requirement, and surely the current limitation as it is

better switch to an already made psu, voltage and current limitted,  took me 3 pcb iterations to get a good morking psu,  from 10ma to 20 amps, a real zero volts to 30 vdc, lm723  can't go down to zero by its design, you have to use tricks

but now it is abandonned, and i got real psus  like lambda kepco kikusui for serious stuff

[Technotronic]

Yes, I kept it on the bracket but used the already drilled holes and widened them for the 2 big diodes.
The thermal sw really belongs on the heatsink with the power transistors somehow as they get pretty hot
naturally.

Would be neat if with some sort of slide switch or 3 pos rotary switch we switch out
the full wave diodes and bring in a fw doubler off the xfmr, then double that with the 3rd
pos of the sw. Somehow I guess the potentiometer running the op amp for bias must also
change to I guess some fixed resistances to properly bias the 3055's and clamp them at
26 and 50V respectively.

and the thermal switch   was the 1st thing to go out loll

[coromonadalix]

but you dont catch the fact its more than a switch addition

you need to change parts to have higher voltage output, it was calculated for the original use, not the one you intend to use

and once again  forget the 50 volts   you will never get it