modified diablo circuit help

[dom44]

I have successfully modified the diablo 2 circuit to run on 60khz but i have noticed on the bench there is thermal drift i take it is from the 555 timer oscillator you have to wait about 20 sec for it to stabilize on turn on when you tune it the slightest air currents make the tuning point drift any ideas apart from putting it in an enclosure to help stabilize the circuit?

thanks