Mojotone Vibrolux 5f11 Kit: Tremolo Thumping

[Johnrcurry]

I've gotten back to this project after some distraction and wanted to report results. I came across a thread on another forum in which the poster was complaining of the same problem in a Princeton 6G2-style amp. The solution that worked for him was to install "snubber" capacitors, including one across the 1M resistor that goes to ground from the grid of the tremolo tube. I experimented with clipping in several values of capacitors I had on hand and ultimately found that a .0047uf capacitor stopped the thumping without noticeably effecting the tremolo effect. I am pleased that the thumping is gone, but it would be nice if I had a better understanding as to why. I also feel as though I've treated the symptom but not really cured the disease. In any event, thank you all for your help.