Tracking down a background hum

[jlucas]

Crack with Speedball that I built several years ago but only get to listen to irregularly.  It occasionally has a slight background hum on the left channel.  It's independent of volume knob, independent of the RCAs being connected and most strangely 95% goes away if the base plate is slightly tipped like so:
https://s19.postimg.org/cvdl00ak3/IMG_20171225_074700999.jpg
Any ideas as to why the tipping helps or where to start investigating?

 

[kgoss]

You probably have an unsoldered connection. Tilting the amp is making a physical connection. Either do the chopstick test or just reflow all connections. Pay special attention to joints with multiple wires.