|I have included this web page by request. I have been sent a number
of Emails from people world-wide, having visited my website and noting
that I used a Marconi M361 in my schooldays, which was many years ago.
They requested further details of this historic equipment. It appears
that although the equipment is very outdated, people still want the thrill
and excitement of getting these receivers to work. I don't know how they
get hold of these remarkable receivers, but I regret loaning my own M361
receiver to a friend over 50 years ago, never to see him or the receiver
I would like to make it clear that I don't have the Service Manual
or the Handbook. The Circuit Diagram of my M361 was located FIXED to the
underside of the hinged lid. The Photograph above and also the Diagram
shown below is that of a Marconi Type 394A Receiver, and I am sure
that they are very similar to the M361.
The main request has been for me to provide the
information on the Power Supply.
|It is important to check the Valve types. This can be done using a
Valve Data Book. (Another item of history). My M361 Receiver was
supplied with 2-volt valves; these were directly heated ( 2-volt valves
were fitted as standard). Some receivers were fitted with 4-volt or 6-volt
The battery supply terminals are situated on the front of the
receiver and suitably labelled.
|Both H.T.3 and H.T.2 terminals should be joined together and to the
positive terminal of a 120 volt H.T. battery.
Terminal H.T.1 should be connected to a 72 volt H.T.battery. (I used
a 67·5 volt H.T.Battery available at that time).
The grid bias battery, which is connected externally, supplies the
negative bias required by the output valve. The positive terminal of the
grid bias battery must be connected to the L.T. negative. For an anode
voltage of 120 volts on the output Valve, then the grid bias voltage required
is approximately 3 volts.
It is very important to check the valve types and also the heater voltage.
If directly heated valves are used they must be supplied with a SMOOTH
Direct Current supply, (I used a 2-volt accumulator). It is very difficult
to provide this from a Mains Power Supply. There have been many circuits
in Practical Wireless Magazine for pure d.c. rectification from the mains
supply, but there is always a risk of 'a.c.ripple' on the output
audio. Later receivers Marconi 394C/12 and 394C/30 used indirectly heated
valves which don't give rise to the same problems.