http://www.amwindow.org/tech/htm/t4.htmHere's some simple mods to make the T-4 Drake line sound FB on AM. (Seven simple steps)
I have personally done the T-4X and understand that the TR3/4 models use basically the same circuitry for AM.
Take out your schematic and see if it applies to your TR4-C. The fidelity obtained with these mods is well worth the effort.
73,
Tom, K1JJ