I have used the 1600 Ohm UBT-1 in several different amplifier topologies.
It is a good transformer when properly used.
Some use it as a 3200 Ohm transformer, by connecting an 8 Ohm load on the 4 Ohm Tap(or 16 Ohm load on the 8 Ohm tap).
But the UBT-1 primary inductance is only 8 Henry.
8 Henry is 3200 Ohms at 64 Hz.
The result of using the transformer this way is the low frequency bandwidth is not very good.
The Randall amplifier uses 3 EL34 tubes in parallel, and the tubes are wired in 'super triode' mode (the suppressor grid, screen and plate are connected to each other). The transformer is used in the intended 1600 Ohm mode (8 Ohm load on 8 Ohm tap, etc).
8 Henry is 1600 Ohm at 32 Hz.