This is the amplifier I plan to use in the project. I got cheap at a hamfest in Aberystwyth, Wales. 

It has a nice metal box, so shielding should not be a problem. Nice sturdy microphone plug inputs, but RCA connectors for the output. I'm not very fond of those, so I might change it.

The whole thing is very much 20th century inside. Only four transistors and a bunch of resistors and capacitors inside. The transistors are 2SC2240s, which seems to be the right choice.