Maximum output is 2 Vp-p into a 93 Ω load. The 1121 is AC coupled at the input, but DC coupled at the output. The output stage is a 12BY7A pentode, V483, biased with 33 mA plate current, which gives a transconductance of about 13 mS. Assuming the tube operates unilaterally, this gives an impedance of about 77 Ω at the cathode of V483. Series output resistor R486, 30 Ω, makes the output resistance of the 1121 about 107 Ω. (Why is this not 93 Ω?)
The 1121 uses a turret attenuator at the input.
The front panel probe power connector provides 6.3 VDC @ 0.2 A for the heater and +120 V @ 10 mA (regulated) for Type P500CF cathode-follower probes.