The ZC1 MkII Transceiver

 I've had this WW2 transceiver for many years but I've never looked insde the case until today. I imagined it used 2 volt valves and had a very low output power but, to my surprise, it uses standard octal valves with 6.3volt heaters. Inside the outer case is the valve layout and you can see what types are used. The types are even referred to by their commercial numbers so are instantly meaningful to amateur radio enthusiasts of the valve era. The 6U7G is a variable mu pentode, not too different from the KTW63, 6K7 and EF39. The 6K8 and 6Q7 are very familiar as is the 6V6, of which one is used as the PA stage in the transmitter and the other as a Heising modulator.


 Here's a circuit diagram and a better picture of the top view of the chassis... Strictly speaking the set is not a transceiver because that term is usually reserved for a set having a common tuning arrangement with a single oscillator designed to work the receiver and transmitter. The designers of the ZC1 were advised to provide two separately tunable oscillators so transmission and reception could take place on different frequencies if so desired. A set such as the WS19 is designed to transmit and receive on a common frequency. However the ZC1 has circuitry which couples transmission and reception together, even including breakthrough operation.

 Below are views of the chassis which bears a passing resemblance to the British Army 19 Set.



 Here's an underchassis view which looks a lot easier to work on than a 19 Set

 The front panel where you can see it uses a preset tuning control different in design to the 19 Set. The calibration of the dials is pretty similar however, using opposite sides for the two wavebands. PA tuning looks to be more comprehensive than that of the 19 Set which relies on an external variometer for accurate aerial matching.

Another difference is the power supply arrangements. The ZC1 uses a 12 volt vibrator and transformer inside the case instead of an external setup. As you can see by the toggle switch adjacent to the battery connector, battery consumption can be reduced by switching off the transmitter.

 Now some close-ups of the various areas of the front panel.


 The Transmitter tuning dial


 Transmitter aerial matching


 Receiver tuning dial


  The identification plate


Another underchassis view where you can see that several components, although not very modern, are not original.



The receiver bandswitch for the two wavebands


 The transmitter bandswitch for the two wavebands


 More views of the topside of the chassis, the first showing a damaged condenser, and next the 12 volt vibrator with the spare missing.. no, I'm wrong.. that 5-pin socket wouldn't fit the 7-pin vibrator so what's it for?



 Receiver tuning condenser, local oscillator and RF



Transmitter tuning condenser followed by PA tank coil and adjacent the two 6V6 valves



 Finally, a view into the outer case of the transceiver


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