Note
QST, Feb 1971, p. 125.
The new Delta 70 linear amplifier is externally identical to the Alpha 70 except for the plate-tuning control; it uses a vernier drive to an air-variable capacitor.
Internally, the only difference between the Delta and Alpha models is
the use of an air-cooled 3-1000Z in place of the Alpha 70's vapor-cooled system.
The two amplifiers are almost identical electrically and handle much the same. Power ratings are identical.
While the Alpha 70 features continuous coverage from 3 to 30 MHz, the Delta is specified for the amateur bands, 10 through 80, although it too is almost continuous tuning.