LM324 Power Supply with variable voltage and current

[mike_mike]

Initial thoughts are, the fans only can be powered from the 2x15Vac transformer.
The tap changer might be able to be powered from the 2x12Vac transformer with modifications so that it can accept negative sensing input voltage.  Because the DVM can only measure positive voltage, it needs to be powered WRT the PSU's negative output. So the unmodified tap changer might as well be powered from the same supply.
 Keep in mind that ground on a Harrison PSU is the positive output.

Can you please be more explicit ? Are you trying to explain that the tap changer could be powered if I modify the schematic ? Regarding the DVM, I didn't understood.

[xavier60]

Initial thoughts are, the fans only can be powered from the 2x15Vac transformer.
The tap changer might be able to be powered from the 2x12Vac transformer with modifications so that it can accept negative sensing input voltage.  Because the DVM can only measure positive voltage, it needs to be powered WRT the PSU's negative output. So the unmodified tap changer might as well be powered from the same supply.
 Keep in mind that ground on a Harrison PSU is the positive output.

Can you please be more explicit ? Are you trying to explain that the tap changer could be powered if I modify the schematic ? Regarding the DVM, I didn't understood.

The tap changer could be powered from the same supply as the LM723 if the tap changer is modified to input negative sensing voltage.
But there is no point because the DVM can only accept positive sensing input voltage so needs to be powered WRT the PSU's negative output terminal and the unmodified tap changer can also be powered from the same supply as the DVM.

[mike_mike]

Do you mean that I need a separate winding on the transformer or another small transformer for the DVM and tap changer ?

[xavier60]

Do you mean that I need a separate winding on the transformer or another small transformer for the DVM and tap changer ?

Yes.

[xavier60]

Do you mean that I need a separate winding on the transformer or another small transformer for the DVM and tap changer ?

That can be ambiguous, you can have the same winding or transformer for the tap changer and DVM but separate to powering the LM327.