Speed,
I’d consider returning if you can’t get help from the dealer and ARC is being difficult.
I’m fairly certain ARC amplifiers use cathode resistors for biasing. If a tube goes haywire and blows a resistor, the amplifier will need to be serviced. This isn’t entirely uncommon.
If you aren’t comfortable soldering, and you can’t get help for a simple LED light, you’ll end up being in the same position again if you get a bad tube.
Manley uses a similar design but they offer “clip-on” resistors so the user can service the amplifier at home.
Good post-purchase support can be critical for tube amplifiers built like this.