This example is one of the last Dual-Band FM radios made by Zenith (the other was the 8H332) for the 1947 introduction of the 1948 model year. A short-lived model, it was quickly replaced by the 7H8202 which used the near-identical "hot chassis" AC/DC circuit but with only the familiar 88-108 Mc band.
The first all-minature-tube FM radio for Zenith and one of the first to use the new selenium rectifiers, this unit is a mix of both the old and the new.
Like an AA5, the sum of the filaments approximates the powerliine voltage with 5x12.6 + 18.9 + 35 = 116.9v eliminating the need for any further voltage drop for the 150 ma string. Unlike battery sets, the filaments are fed with ac reducing the load on the Se rectifier.
In this case the design is much later than that of the 8H332 mentioned above since the eighth tube in that unit is a 5Y3 rectifier, unnecessary with a Se rectifier and nearly identical to the 1946 chassis 8C20 design except for the partial substitution of minature tubes.
Also a feature of this radio is the inductive tuning of the FM band for more precise tuning. This was also used by Zenith through the 1961 Transistor Royal 2000 Trans-Symphony.
Note that this unit reflects the first use of what was to become a Zenith trademark, the large circular dial directly over the speaker cone with a variable tone control at its center, something continued in most AM-FM table radios through the 1960 C835R.