[morzh]

I alsoo found as a kid, not as hard - I simply was buzzing a transformer's primary with a tester and when disconnecting I felt a bit of a ...not really a shock but it was certainlt electric and it was certainly higher voltage than that that does not produce unpleasant sensations.
Then I read up on it and since I only use one hand when buzzing large coils.

The flashovers in tube amps when musicians plug speakers hot.
Certainly if the speaker is soldered in, there is nothing to worry about and caps could be sized for the B+ only.
In an unlikely event of the speaker disconnect....one time probably nothing bad will occur.

But with pluggable speaker and people not nowing better....yes, there could be that Tesla coil effect.