I clean SMPL and others with a rotating brass brush (soft and slow).
Between 3 mods I exchanged parts to get better/full "start on" power.
Result:
The problem seem to be the 8(?) to 12(?) notches in the switch.
They seem to make not always the best contact to negative:
you hit the button left side: OK, you hit right side: not OK.
It seems the mod is worn out, too much play between electric parts.
I think I need some new tube mods,
but what to buy?