Looking for any info on a Symphony Porto-Amp made in 1948.  Small 3 tube practice amp @ 12" x 12" x 5".  One knob labeled "Volume" and two inputs labeled "Instruments", runs on 110 Vac wall power,  8 inch speaker.

Has a removeable front cover that is covered in it's original fake alligator skin material, back cover is covered in the same material.

 Looking for some advice concerning injecting a test signal into a fender Princeton Chorus amp.  I have some modest experience troubleshooting electronics but this is my first go at a guitar amp.  The factory schematic calls for a 1 kHZ input signal in order to achieve the signal values listed at the various test points on the schematic.  However the schematic makes no mention of a voltage requirement for the 1 kHZ test signal.  The first test point in the signal flow is "TP9", a tie point right after input jack #1.  The signal value listed is 2 mVAC.  Should this be the value of my 1 kHZ test signal?  My next question is a bit of a newbie no-brainer but I want to be sure...to inject the signal do I just take an old guitar cord jack plug and attach a couple of leads to hook it up to the sig gen and amp?
Attached is a cut of the input for the amp.  Thanks in advance!