I just received my new practice head today to go atop my Carvin 410 for my apartment. It is an old solid state Ampeg bt but Im not sure of the model. On the schematic inside it says BT-25, BT-25L, and BT-140. Just curious if anyone knew which one this was (from the posted pictures and url link) or what year it is from? The serial number on the back is 088777. Also when playing it for a longer period of time the heat sinks on the back seem to heat up a lot. I was wondering if I should be concerned about this or if there was a way I could install a fan (mostly just finding a wire with the correct voltage). Check out more pictures of it at here http://people.msoe.edu/~gerkea/amp/amp.htm Thanks!