power supply questions

[mcfarlane_audio]

so, as im working away at my MCI console rebuild project (an MCI 416A), i have run into a huge snag with the power supplies, basically they are shot, but im fairly confident that the transformers are still good, so, in the hopes to avoid the tracing problems through the old design i figure we can do better (now that its 2007 and not 1970) so i have been browsing the power supply meta for a few weeks and have come up with:

the JLM power supply, (link here : http://www.jlmaudio.com/JLM ACDC Schematic.pdf )now i know that it was not designed to run a whole console, so there would have to be some modifications, this is where i get lost, i cant seem to find transistor or current limiters with the specs that i need, hoping to dive into and rip out the transformers this week, but any help woulf be greatly appreciated along the way. (as inspiration ther will be spare transformers (belived to be jensen) up on the black market when im all done :grin: )

here are the specs (copied from blevins audio)

CONSOLE POWER REQUIREMENTS:
LAMPS: 21V DC Bipolar @ 1.5 Amps
RELAYS: 24V DC Bipolar @ 2.3 Amps
AUDIO: 24V DC Bipolar @ 1.4 Amps

POWER SUPPLY SPECIFICATIONS
ELECTRICAL:
Three interchangeable power supplies are used.
Voltage outputs are determined by connecting
Appropriate power cable from console.

VOLTAGE: +21V DC or +24V DC Bipolar
Regulated to Less than +1% for Inputs of 95-135V AC and outputs up to 3 Amps less than 1 mv ripple.

CURRENT: 3 Amps normal output. Current limited to 3.4 Amps – at this point the Output voltage goes to zero.

thanks again, -Brock-

 

[Samuel Groner]

Have a look at the LT1083 or LT1084. For the relays and lamps you may consider the use of a simple zener regulator.

Samuel

 

[amorris]

dont forget to make sure that the console didnt take out the power supplies and build these just to have the same problem. usually the bridge rectifier goes in these and the caps. otherwise its usually a module that takes them out.

 

[mcfarlane_audio]

the reason i dont want to rebuild the old ones is because the regulator cards (full of dc feedback stuff) are missing in 2 of the supplies and one of the supplies looks like it spent some time in a pool :shock: , its also not the most efficient way of doing things, so i figured i could reuse the transformers to save me some $$ and DIY the buggers using a newer design, although the power one HCC24-2.4-A looks like almost exactly what i need, it will run me 110 bucks a piece, they do have them at allied though, thanks again everyone,
i also dont know how i missed the LT1083 or LT1084, thank you Samuel, more suggestions are welcome

 

[mcfarlane_audio]

ok, so after some thought this is what i think i have come up with, one of the transformers is shot, so i need at least one new supply, i figure ill buy one HCC24-2.4-A and use it as my audio supply, then rebuild the other two, from the JLM schemo to use for relays and lights, any problems with this idea??, ok, now for the dumb question, can i use an lt1083/4 for both the posotive and negative leg?? i cant seem to find any neg voltage regulators, so im assuming yes?? Thanks again, i really do appreciate the help, thanks for the tip amorris, but i think its some inner working of the regulator card, the caps and rectifier seem to test out ok, and all the strips came out for the rebuild so its not a module, thanks again, pics to come soon!

 

[Sorr]

I have just built a new supply for a 48 channel Trident.
I used two LM338k regulators for +/- 17.5.
In the negative regulator the O/P of the 338 is connected to ground and the minus is used as the -17.5. (This was done in a number of consoles including the TAC/Amek Matchless).
This requires two secondary windings!
The bridge rectifiers are 25A, 22,000 mfd filters with 0.1-1mfd right on the input of the regs.
I used a 3A protection diode across the LM338's. 27 mfd 63V across adjust resistor and 10 mfd 100V on the output.
And another protection diode across the 120 ohm resistor from O/P to adjust terminal.
Do not exceed the 35V I/P to O/P.
If that is a possibility then use three 6W 10V zeners in series across the 3A protection diode.
For the lamps I used a LM350.
For the relays I would use another LM338k