I'm trying to clone a early 80s sound device which uses several supply voltages: +/-18V, +/-14.5V and +/-4V
The schematics of regulated +/-14.5V using LM723 is attached. I get -14.5V from emitter but the temperature of the TL081 and 2N3906 is too high. I have killed one 2N3906 letting the circuit working for 4 minutes. The original schematics is also attached, the only difference that it uses one of four opAmp of TL084 instead of my implementation with one TL081. Any help on this temperature issue is appreciated.

 

hi Delian,
Welcome to AAC.
Will tidy up your images.
E

 

hi,
What is the current load for each of those supply voltages.?
E

 

There is no load at all for now... and I get 68°C on the surface of TL081. I even try to change the TL081 from TI to ST and other...

 

hi,
What are the power rail voltages on the TL081 OPA.?

 

In the LM723.png : +14.5/-18V

 

There are two presumptions in answers on on my post at the EE SE
1. The absence of base current resistor
2. The wrong case of TL081

 

You have a high current drain. There is something that acts as a load.

 

The load of -14.5V is detached from the board so I completely sure that there is no load for now.
But I can cut the 2N3906 collector from PCB to check will the issue be eliminated. If so, what are the methods to find the reasons for high drain?
The daughter board that you may see on the picture attached is completely removed and all other -14.5V consumers are desoldered.

 

hi Delian,
There is about 0.5Watt in the transistor and 1Watt in the TL081
E

 

hi Delian,
There is about 0.5Watt in the transistor and 1Watt in the TL081
E

I have also gone this way... simulated this node ... getting the same values, that means "IT HAS TO WORK"

 

eric - Q1 is a 3906 PNP.

Separate from that, Q1 is operating as an emitter follower, so depending on the circuit's operating point, a base resistor is not mandatory. Here is a circuit variation that shows the negative output pass transistor and the output voltage divider in a more traditional arrangement:

ak

 

hi,
The -14.5V is Output voltage from the 2n3906, with a light load the components run cool, where is the-14,5V connected too.?

Woops thanks @AnalogKid.... ref the TS's drawing error...

Eric

 

eric - Q1 is a 3906 PNP.

Separate from that, Q1 is operating as an emitter follower, so depending on the circuit's operating point, a base resistor is not mandatory. Here is a circuit variation that shows the negative output pass transistor and the output voltage divider in a more traditional arrangement:

ak

Yep! I have this high current PSU working for 8 years for now. And I thought about rebuilding the part of the circuit. But the original schem is working fine. I want to find the source of high drain...

 

hi Delian,
Looks OK with correct transistor.
E

 

I'll try to desolder the emitter of the 2N3906 to check. May be it is the defective PCB issue?!