Help with a rotary speaker motor?

[rufustf]

I know it's not a leslie simulator stompbox, it's a small 10" speaker leslie w/ a 12/24V 300ma motor.

I had another post up about controlling the slow speed of this leslie kit (rotary wave from songworks.com) but I resolved that issue only to find another. It came with a 9v 300ma wall wart.
I got rid of the wall wart and built a simple power supply from a 12V/2A transformer. There are two rectifiers in parallel on the T leads: one goes to a 7805 regulator to supply a relay to switch the slow/fast speeds, the other to power the motor. Both have caps to gnd.

The relay puts a 6 pos. rotary switch with some very low resistances in line w/ the motor. It's crude, but it's working fine and when engaged exhibits no problems. I'm throwing that in for clarity, while I get to the source of my troubles.

The "heart" of the motor speed control was a 317 regulator that has a 500 ohm pot w/ a 75 ohm (?) resistor across it on the adjust leg. (Resistance is about 60  something ohms across the pot on the meter). Tied from the adj. to the out is a 174 ohm resistor. A good fast speed reads about 1.8 to 2.1 volts on the motor. Unfortunately, it's short lived.

So, here's what happens: I turn it on, it works great w/ both speeds for about 30 - 45 seconds, then the fast speed starts to slow. When it hits about a volt it stays. Figuring that the 317 is being pushed to draw too much current, I swap it for a lm350. Same thing happens with the beefier regulator.

Now, I'm thinking I need to play with some resistances on the regulator to get this thing to sit tight at two volts at the output, but this is where my knowledge fails me. What value resistors should I try? should I use a different pot?  The 317 wants to see 1.25V at the output, but I don't know if the 350 wants the same deal.

I know that there are probably better ways to do motor circuits, but I'd like to work with what I already have, especially since the slow speed is finally about perfect.

When I draped a resistor across the regulator, I melted the tip of my clip, so I'll employ the homemade alligator clip wire for this one for any recommended tests.

So, who knows how to tame this simple 24V motor (not a stepper)? Again, what's ideal is a steady 2.1V on the regulator output.

Jason

ps-If it's more helpful I can try to do a sch. of the thing but I thought that explanation would suffice.