Cary V12 - Output Tubes Problem

most-likely that is the fault of a power supply and less-likely you'll be able to perform that troubleshooting by yourself if you've never worked with high-voltage circuits (nearly 500V).

there are definitely fuses on the amplifier and i guess one main for power supply and the other is an output fuse. changing these fuses will unfortunately less-likely help.

were the previous tubes blown? did you try them on another side of the amp or placing them onto the working monoblock?

sorry i made a-bit unprecise statement about power supply which truly meant to be the individual DC supply for the tubes that might be for a few at the same time depending on the design topology.

the mentioned resistor-fuse circuit protection as mentioned by Catman is integrated onto many amplifier brands and I guess with the simple 10Ohm/5...10W bias-measurement wire-wound resistor. the grid supply resistors 1k...5k can also act like fuses if something happens with tube or outside(grid-cathode shorts).

these problems can be easily traced with multimeter when the amplifier is off BUT discharging powerful filter caps is a-must before even touching anything on the circuit. use 1k wire-wound resistor(RadioSnack is OK) with isolated clip leads on each filter cap and any high capacitance caps.

when the problem is identified in order to properly fix it you need to carefully replace the faulty element without damaging next-standing elements(use heat sinks for soldering) and without boiling the solder(use 15...20W setting on your iron). use tin/silver solder that is more strong and heat-proof.