Distorting reverb tube

[Tomislaw]

Looks like the problem is gone and the solution was pretty straightforward. I decided to try the 12AU7 as the reverb driver which was a move in good direction, but the tube would still start oscillating if the volume was too high. I then disconnected the cathode bypass capacitor and that finally stopped the oscillation and lowered the maximum signal swing to around 260Vpp with the stock Rk value of 2K2. I changed it to 1K6 which yields 300Vpp at the plate and just about enough reverb. The tube seems to still have some headroom as it wouldn't oscillate even with values below 1K, but I think I'll leave it as it is right now.