ARMY wireless senders C42 and C45

My partial extract of the EMER (manual) for the C45

(EMER....Electrical and Mechanical Engineering Regulations)

The wireless set C42 and C45 were vitually identical set covering differant frequency ranges.  The C45 cover the high HF range and the C42 covered the low VHF range. They were wideband FM transcievers with a one band wide coverage transmitter and double converstion radio. They used differant construction methods to the C13 radio but were still biult like the tanks into which they were installed.   They appeared in large numbers in the surplus market from the late seventies onwards. Many hams succeeded in getting these rigs on air, unmodified , onto 6 meters and some onto 10 meters.  At 52 Mhz the front end 6AK5 was less then optimum noise figure and benefited from even a low cost transister rf amp to improve noise figure.  They were not really suited to "narrow band" FM chanelised operation as they lacked the repeatability to put the carrier into the narrow if range of converted commmercial low band FM transcievers.  However, with a counter on hand, they could be reliably put "on channel".   The transmitter portion had a nominal 10 watts output.  My C42 would often contact via tropospheric ducting paths between Melbourne and assorted Queensland locations during the Xmas season when many hams were off work. However, in the early eighties many Melbourne hams had C42s working and  CQs were allways answered on 52.525Mhz and 53.5Mhz.  

I never got a manual for the C42, however a I obtained  a zillionth generation copy of part of the C45 manual which proved to be the same circuit, for all intents and purposes with only the LC constants differant.

Presented here are the schematics for the C45, scribbled on the anotated by myself, many years ago. They are 3rd generation photocopies done about 1977 and recently "imaged enhanced" with the GIMP. My usual advice is still , best to goto and follow their procedure for downloading the EMER manuals which are of much higher reproduction quality.

For those lucky hams who have the C45, they can be used on the 10 meter band, there are even a couple of 10M repeaters in Australia, however you would need a pair of C45s to use the repeaters due to the RX TX frequency split.  

For those wishing to restore or repair their C42 and may not be of a sufficiently advanced vintage to understand the finer points of vacuum tube technology , my advice , simply is this.  It is possible to repair and maintain this set with nothing more than a multimeter and a digital frequency meter.  First step, check ALL resistors, especially screen grid droppers and anode loads, they will have drifted too high after 50 years. Then check all screen bypass capacitors for leakage. If a tubular capacitor says "HUNT", just replace it.  Millitary spec valves of this vintage "never" failed.  If your C42 does not quite work, it is allmost certainly NOT due to a faulty valve!  Nevertheless, check that all valve filaments light up, and that no silvery getter material on the valve envelope has gone white. White means the vacuum seal is broken.
A signal generator for checking the radio is pretty much essential, however if you live in an area with lowband television, then a piece of wire and the set tuned to the video carrier  (56Mhz)  will do.  To check the transmitter, ( you should be or know a ham ) you need
dummy load and frequency meter.  Operation with other hams on 52.525 Mhz FM calling chanel that use narrow band crystall locked and crystal filter converted low-band FM transceivers is possible if you keep peak deviation down and monitor your actual transmit frequency with the frequency meter. The DFM is a must, the film strip dial repeatability and settability  is good, very good, state of the art in 1955; but it is not good enough for the "modern" transceiver.  On air use requires the use of a low pass filter if you need peacefull and happy non ham neighbours!

Australian hams may only use the  set C42 between 52 and 54 Mhz, so sadly, no prospect of "rare" DX on this set for me.

RHS of schematicmiddle part of schematic
LHS of schematicgeneral system block diagram
the seperate power supply unitC42/45 power requirements
PSU output pins and voltages

and dont forget to look at some power supply designs

And thats all of the C45/C42 EMER (Electical and Mechanical Engineering Regulations) manual that I possess. The most complete
manual for this and all the Larkspur series radios can now be obtained from  

I am not allowed to reproduce the royal signals EMERs here. it is well worth the effort to take the time and trouble to register
with the site and get the download permits and keys.  The royal signals people appear to have available scans from the virgin first  generation documents and their scans and retouching is off the highest quality.


you are most welcome to email me at

Thu Jul 17 19:23:25 EST 2008 added repair note, email sig