This one was made by the perfectionist James Millen Corporation, their "Junior" model (manual for 92201 here), rated at 150W continuous, 300W peak:
Internal construction is as clever as most Millen devices. The split-stator input variable condenser sits on top of a little copper-plated box and the input connector is at the rear-wall end of the box. What's in the box? A standing-wave bridge, a pair of directional couplers for providing equal-
The output capacitor stands on ceramic pillars: both sides are at an RF potential above ground.
On the back panel, an extra connector! It connects to a one-turn loop coupled to the main coil (see the manual), and provides a sample of the signal for an oscilloscope or keying/modulation monitor.
Found on an auction site for a remarkably low price, this example is unrestored. Typical of Millen products, it is overbuilt and will only need attention if the meter movement or passive components in the SWR bridge (two diodes, two resistors, a fixed condenser or two) are damaged.