I found a keyboard amp at pawn shop for really cheap this week. The amp is an old Stage (univox) 720k, solid state, from the mid 70s. Everything is working perfectly but the reverb tank is missing. By the look of the amp it's easy to tell that it's been in a lot of shows and the previous owner must have removed the reverb tank. So, how can I know what reverb tank I must put in it ? There's no information at all on internet about that amp. I found the schematics here : http://www.schematicsunlimited.com/u/univox/univox-stage-720k-keyboard-amplifier-schematic but it's not really helping me (I'm not really good in electronics and I don't understand it). I really want that reverb back.