Class D amp Transplant ( Like Post#2):
In Dec 2023 I repaired a vintage 30W Electar Guitar amp that had a big pcb containing front panel tone controls etc, and a Class B amplifier at rear.
Amplifier was blown up. It was a DC coupled amp something like an op amp with discrete trasistors.
With no circuit and tracks melting off, (Hold my beer, ) I put the board in the scroll saw and cut off the amp section !!
Purchased Newark part 53Y1822 ~$17, a 2 by 15Watt single board amplifier by SURE Electronics. Instruction sheet showed how to connect as single 30W.
DC Limit for the Class D is a strict +26V, so beefed up the amp's + supply and made a +24V regulator from the one of the original ouput transistors.
The amp now gives 14Vrms into the original 4 speakers with equivalent 8 Ohm.
One item to be careful of, the output is offset at half of the +DC supply. So I removed the external speaker socket.
For present case, search on Newark "SURE Electronics" show a range of these Class D boards rated up to 400 Watt.