[morzh]

Koik,

Here's how.

1. Buzz across the field coil. Should be 1.7 kOhm.
2. Take your variac, preferrably plugged via isolation xfmr into 120V outlet. Set it to 20VAC output. Connect the output to your output xfmr PRIMARY. Turn it on. Take a small magnet, not too strong, the type you could hold in hand without it flying out and gluing itself to the speaker pole, as it can damage coil or cone - hold it firm, and move it towards the voice coil fom the front. Again, do not let it out. You should hear the 60 Hz buzz when you close enough. Another way is just to tempirarily place small magnet right to the top of the pole, but then you will need to take it off and it is inconvenient once it is there since the voice coil is around. You could try a very strong magnet from the back of the pole, might work too.

All this is for you not to have to power the Field coil.
So, if the FC is 1,700 Ohm and the spiecker hums, it is good electrically.