Here is an identical pair Hammond Rola AO 21055-2 Field Coil Speaker for Sale, including a pair Field Coil Power Supplies for the speakers.
Field Coil voltage is 110 V DC at approx. 160 mA.
This Speaker is rather a Full Range Speaker than a Woofer.
High efficiency, I think over 96dB/1Watt.
I have used a Darling 1626 SE Amp with 0,7 Watt RMS to drive the speakers, was absolute no problem.
I have used this speaker in an open baffle configuration, see picture, only marked position is for sale.
If you have further questions, please send a message or call me.