A 71A should drive the 100A very well. There is an adjustment on the driver pin/magnet gap on those 100A's that can have quite an effect on volume, but it's been too long since I messed with one to remember the adjustment procedure. If the speaker works well with other radios, then I wouldn't mess with the adjustment. Those 100A speakers were one of the best sounding of the day, almost hi-fi by period standards.
