I see, in that case well done....

Don't worry about the op-amp, I've decided to start fresh and build a circuit from scratch using all new parts.
I've built the circuit, well two of them, and have been testing them for the last couple of hours. I had one with two motors running to make sure it could handle the pressure.
worked fine I'm glad to say.

I'm actually building them for my valve amp and wanted something small and tidy. But they will work the motors just as well, in fact they have been

Low part count, easy circuit as most of it is in the chip and even that only has 3 connections.
Bits you have as follows....
one rectifier, two caps, one transformer
Bits you don't have
one 1k lin pot, one chip LM1084 rated at 5 amps,
You will need something to mount it on and some wire, which you may have...
There really is nothing to it if you are interested I can give more details. It will run 12 & 24V motors.
Mine need to run at 10A each for the valves, so I'm sticking a 2N3055 on the end, well a pair of them in fact. You can do the same, it's simple enough and would help the LM1084 to run cool instead of hot. But it can take it. Besides it has it's own build in protecting circuit so you can't damage it anyway.
If that all sounds too much, don't worry I can show you step by step if need be, I can always build another one and do a post a day for each component with pictures

When you have done it once you'll find all sorts of things you want to power and make some more......
