[af024]

Actually, perhaps that's not a good idea on my part (increasing the connected resistances at pins 5 and 6). I'm also not sure about the max rating of the LM317T. I mean there's circa 42Vd.c. supply to deal with. I don't know what the IC will pull in terms of current, but how if I used a series 68 ohm resistor off the 42Vd.c. supply and take that to a 1.3W 24V zener diode with, say 470uF strapped across it and use that as the IC supply (then take the other resistor values back to where they were)?

I'm still at a loss when it comes to selecting suitable values for R1, C1 and C2 (even though I've read the datasheet several times). Pages 4 and 8 seem relevant.