[jrblasde]

Ah, very clever. Just an increased voltage rating, but it need not be a safety cap?

[morzh]

No, you do not need a safety cap.
You need a high-voltage cap, 1200-1600V, but even that is mostly due to the fact that if a speaker is pluggable (not hardwired), unplugging it could create a flashover on the transformer (high voltage at the primary).
In the normal operating mode the voltage there is B+ and 500V rating is quite enough.
I do not even use high voltage caps as I do not unplug speakers while in operation.

[jrblasde]

I wouldn’t ever think to disconnect the speaker while the radio is powered on. Not at these voltages!  But, what can I say? Common sense is not so common after all.

[morzh]

What I do not know if they were planning for bad connection and arcing in the speaker connector, or a sudden voice coil open, or...or just to have an idiot-proof design. I mean, things are possible. But also not very likely.

[jrblasde]

All are fair points. I’ll utilize the higher voltage rating. I might as well spend a few dollars more to protect the transformer. We’ve worked so hard to get these transformers cleaned up!