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Swedish superhet receiver
The MA-444 was a valve-based superheterodyne receiver, developed during WW-II
by MILORG/SOE-Section Norway and built by an unknown company in Sweden.
The receiver was mainly intended for use by the Norwegian resistance
(MILORG/SOE-Section Norway), for listening to the coded messages that were
hidden in the news broadcasts of the BBC in London.
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During WW-II, the Norwegian resistance MILORG listened to
the news broadcasts of the BBC in London. Hidden in these broadcasts were
coded messages, informing them about droppings of weapons and other equipment
and giving them further instructions for sabotage actions, etc.
In September 1941 however, the Germans ordered everyone who was not a member
of the Nazi Party, to hand in their receivers. As a substitue, the MA-444
was developed by the SOE-Section Norway (i.e. MILORG technical
personnel operating from the UK).
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The MA-444 was built by an unknown company in Sweden and is also known
as Svenskesuperen (the Swedisch superhet). The picture above shows a
pristine example of the MA-444. The receiver was connected directly to the
220C AC mains and had a connection for a high-impedant
pair of headphones
(2000 ohm) at the rear. A single wire antenna was connected to a
socket at the top.
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The image on the right shows how the head-phones were
connected at the rear
of the unit. A correct polarity is important, which is why one of the sockets
is marked with a red dot. The circuit diagram, reconstructed by Tor Marthinsen
in 2000 [3] reveils that the speakers are connected in series with the anode
of the 6Q7 valve.
In order to keep the price of the unit down, it was built on a simple
chassis and consists of just 4 valves.
The frequency dial is visible through
a circular window at the front, but is in fact a simple piece of printed paper
glued onto a disc.
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The components are protected by a perforated metal case, that is similar to
a case that Siemens used at the time for antenna amplifiers [2]. The case
provides sufficient shielding and ventilation at the same time.
The radio was suitable for the reception of phone (AM) and telegraphy signals
on frequencies between 15 and 50MHz.
The two knobs at the front are for tuning and volume.
The MA-444 was produced towards the end of WW-II and most units
were delivered by the so-called borderpilots to Norway [1]
[2], where they
were used alongside other clandestine receivers such as the Norwegian
Sweetheart. The Sweetheart was a battery powered
device, intended for use in the field, whereas the MA-444 was a desktop
mains-powered receiver.
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The circuit of the MA-444 is build around three valves:
A 6J8 as HF mixer and oscillator, a 6K7 for the IF stage
and a 6Q7 for the detector and the AF output. The IF frequency is at 432kHz.
A fourth valve (25Z6) is used as rectifier. The 2000 ohm headphones are connected
in series with the anode of the 6Q7 AF-amplifier.
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- Louis Meulstee, Wireless for the Warrior, volume 4
ISBN 0952063-36-0, September 2004.
- Erling Langemyr, Svenskprodusert radioutstyr benyttet i Norge 1940-45
Hallo Hallo, Nr. 67 (3/99), September 1999, p. 17.
- Erling Langemyr, 'Svenskesuperen' MA-444
MA-444 circuit diagram reconstructed by Tor Marthinsen (2000).
Hallo Hallo, Nr. 78 (2/02), May 2002, pp. 20-22.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Tuesday, 25 September 2012 - 17:34 CET
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