Elektor Lab Power Supply Oct/Nov 1990

[smithy666]

I built this project some time ago (it was published Oct/Nov 1990 in Elektor), but I have never been able to get it working properly. It switches on ok, you can change the volatge from 0-40V, both channels operate independently & tracking but as soon as I apply a load the transformers make clicking sounds and applying a 50W load with say 20V 2.5a, the fuse blows (5A slow blow on 240V). It seems the preregulation circuit is not working correctly. Has anyone had any experience with this project or can offer guidance?
Thanks, Chris

Schematic:

[smithy666]

I received an errata on the project, so following the mods I now get both channels working in independent & tracking modes from 0-40V and current up to about 4.5A. There still seems to be a loud buzzing/sort of ticking from the transformer when under a load of 2A or more. The errata said the ticking was caused by overshoot in the pre-regulation circuit and the mods suggested should solve the problem. Monitoring the main filter cap (C26) with an oscilloscope shows the cap is being charged every cycle (actually 2/cycle), which seems correct. My guess is the buzzing/ticking is still occuring from too much amplification in the regulation circuit. Is this correct and what should I do to reduce this or has anyone else still had this problem after implementing the suggested change? The schematic of the change is attached - what should I change to reduce the gain?

[peranders]

I'm afraid I can't help you but if you don't get any answers here you could surf over to www.diyaudio.com Over there you have a couple of good people, "eva, "janneman" and some more.

[teknofix]

Hi, I am also looking for info for my unfinished Elektor Power supply,can not remember the exact year, I think it was issued back in 1985-1990 futured Lab Power Supply, using LM723 and two LM741 and 2N3055 output transistors.
The front cover of this isuue was green and Twisted Ribbon Cable was pictured on the cover, I wonder if you could possibly identify and locate this issue for me to obtain needed info.for this circuit. Thank You. [email protected]