[mikethedruid]

That speaker should work fine. To test it, just tap the leads on a 1 1/2 V battery. You should hear clicking in the speaker. I suggest you not use the power supply for the filaments. Get a small 6V motorcycle battery and a cheap charger for it. For the B supplies you can use the power supply if it is well regulated and smooth. I would buy some C or D cells and make 4 C batteries by wiring sets of 3 each in series. This will allow you to cut in 4 1/2, 9, 13 1/2, or 18 volts for the C voltage by adding C batteries in series until you find what works best. I think it will be 18 V, looking at the characteristics of the '71A. The C battery draw is very low, so these batteries should last a very long time.