L200 Bench Power supply.

[audioguru]

The absolute maximum AC supply you can have from the transfomer without exceeding the rating or your 741 is actually 32V

Nope.
Two of the opamps have a negative -5.6VDC supply.
So the max allowed AC voltage for 44V opamps is 28VAC. But a 28VAC transformer will be about 29V or 30V without a load.

A 26VAC transformer would work but is not available and produces an unregulated supply voltage that is too low. A 24V transformer is available but also produces an unregulated supply voltage that is too low. The original project spec's a 24VAC transformer with a current rating that is too low.

 

[Hero999]

That's true.

Hang on a second, the MC33071 will work with the inputs down to the negitive rail which will eliminate the requirement for a negitive power supply. Granted you'll need to modify the ofset trimming but it on the whole, will simplify the circuit.

 

[hackableFM]

Right, Sorry for the late reply guys.... I've been away on holiday for 2 weeks!

Anyway, I'm back and this PSU is now built. It worked on first switch on! The one thing that surprises me is that this thing's output voltage is adjustable from 0.00Volts up to 34.4volts! Neat ehh?

@ Audioguru, I might just be the first to have built this thing with your suggested BD139! It's in there and working! Are there and tests you want done with it using this transistor?

I must however admit that I have only used the original TL081 I.C's, I couldn't source any of the higher voltage ones. If they blow up then I will spend more effort in sourcing the higher voltage versions as suggested. All other modifications have been made though, I am using Higher power rated resistors in some places (i.e. 25Watt instead of 10Watt) and I have doubled up on some 6Amp diodes for the rectifiers.

Boy am I pleased with this already, I have been into electronics on & off for about 20 years and up until now I managed without a variable PSU!

MANY THANKS!! to all of you who helped me through this build... Without you I would be in need of a toupee by now!

hackableFM....

 

[Hero999]

I'm glad to see it's working.

It always amazes me at how far you can push some components past their absolute maximum ratings and they still work. I remember building an LED flasher with 74LS00 NANDs and it still worked even when I powered it from an unregulated walwart set at 12V. The LS IC is only rated for 5V and the wallwart must have pumped over 18V in to the thing and it didn't even get warm!