The Mk II was a development of the Mk-I and its design is
generally attributed to RJ Orbell of Radio Ltd. The significant
differences between the two are as follows.
The Mk II is dual band having an LF band of 2 - 4 MHz
and an HF band of 4 - 8 MHz.
A synchronous vibrator was used dispensing with the
need for the two 6X5 rectifiers. (6X5 rectifiers were almost
The switchable HT voltage feature was dispensed with.
Other improvements were the tropicalisation of components
and improved sealing and weatherproofing of the case, repositioning of the
antenna matching controls and meter, replacement of battery terminals with
plug and socket, relocating the lamp socket to a more central position and
other minor changes often dictated by the availability of specific parts at
a given time. The use of special flux solder as part of the
tropicalisation process initially caused many assembly line problems with
it's much higher melting point. One complete batch of 50 sets is
reputed to have been rejected and returned to the manufacturer by military
inspectors because of dry joints and generally poor soldering when the new
solder was first introduced.
Official records show that the Mk-II was originally
planned to have a UHF transceiver included in the design matching the No. 19 set.
The UHF section was to be an associated stand alone unit with it's own power
supply. This idea was not followed up, although prototype
UHF modules for this project were designed and constructed as a joint effort
between Collier and Beale and the NZ Post Office Radio Section.
Key components such as meters, valves and
the main tuning capacitors were all of Australian, American or English
Wellington based Radio Corporation was given contracts
for the production of the ZC1 Mk II as was Radio
Ltd of Auckland.
In all, it is now believed that
a little over 9,500 ZC1 Mk II sets were made.
A number of ZC1 Mk-2
sets were issued for use on the "Home Front" inside New Zealand in the last
months of the War. This is the only recorded service seen by the ZC1 Mk-2 in WW2.