AG, an eight Ohm speaker is shown on the schematic, rather than four Ohms.The original amplifier with a +-25V supply produces about 40V p-p which is 14.14V RMS which is about 50W into a 4 ohm load. The amplifier is class-AB so which is about 60% efficient then the total heating of both output transistors is about 40W or 20W each which is fine.
When the supply is increased to +-52V then the amplifier output is about 92V p-p which is 32.5V RMS which is about 265W into a 4 ohm load. The heating in both output transistors will be a total of about 175W which is 87.5W for each output transistor and they will melt unless you cooled them with a huge heatsink, a high velocity fan and maybe some liquid nitrogen. The driver transistors will also get too hot and the circuit will need to be re-designed to supply the very high current. For such high output power amplifiers use paralleled output transistors.
Hi Micas,I wonder what to do to use a complementary pair of transistors (2SA1493 and 2SC5200) in the output of this amplifier (attached image) increasing the supply voltage to + -52V.