I just got an Ibanez Valbee 5-watt VBG and I was wondering if it is possible to mod this amp to add a footswitch, because the distortion tone is great. I was planning to buy a multi-effects pedal, but if I can't use tube distortion, better not!
No, because it wouldnt do anything. No channels to switch or reverb so it would be pointless. And to mod it to be able to switch from clean to OD would be extremely difficult
Try to see if you can get an actual schematic, with components and values. And we can be more helpful. Since you don't have channels to switch, the only thing you could to with a footswitch is control the boost, but that may be what you want.
Yes, controlling the boost on/off is exactly what I want to do. What components do I need for a footswitch? I suppose something like a relay, or some switch...
Take a look at the boost switch. If it is a simple ON/OFF SPST jumpering a resistor, then what I think you will need to do is replace the current boost switch with a 1/4" jack. So you would solder the hot lead from the switch to the tip of the jack and the ground lead to the sleeve. This is what you will plug your footswitch into. The footswitch itself will consist of a 1/4" cable coming from an enclosure with the tip wire connected to a side lug of a SPDT stomp switch and the sleeve wire connected to the middle lug.
Basically, all you are doing is extending the wires to move the switch out of the amp.

I haven't tried this, but I think it would work.
This description will only work if your current boost switch is simply an ON/OFF switch. If it's something different, then we'll need another plan.