O-10 is a Push-pull plates to line transformer, 30,000 ohms plate to plate, secondary 50, 200, 250, 500 and 600 ohms. Fairly low power, think in terms of milliwatts, not watts. These are the diminutive UTC "ouncer" trannies, they're very small. 600 ohms was the "industry standard" line impedance for broadcasting and most "pro" audio, back in the day.
Might be good for a dandy little line stage, use a 6J6, 6DJ8, 6CCG7 6FQ7 or 12AU7 as the "power tube" in P-P, then use the 600 ohm secondary for the line output. Might also be good for driving
very efficient 600 ohm headphones. Flea=powered PP amp for each channel.
MC usage, connect the cart to the low z winding, the 30K winding to the input of the phono stage.
Grab 'em if you still can, they're a treasure!
/ed B