[Synchrodyne]

From its TV AGC papers of 1957-58, one may infer that for positive/AM TV systems, Mullard preferred to use remote cutoff valves in AGC’d positions, although the sharp cutoff type was seen as being acceptable for negative/FM systems.

The PCC84 comprised a pair of sharp cutoff triodes that when operated in series cascode, had a net remote cutoff characteristic.

The PC88 had sharp cutoff triodes that in combination provided a sharp cutoff result.

The PCC89 had remote cutoff triodes that in combination produced a curve similar to that of the PCC84

So, given its preference, it seems reasonable that for UK domestic production, Mullard would have stayed with the PCC84 until the PCC89 became available, rather than switching to the PCC88.

Mullard described the PCC189 as the PCC89 with a different pinning arrangement that facilitated alternative positioning of components in tuner units.


Cheers,