[Dept. of Computer Science]

Radiomarelli 9A75E

Our Department and University.
See my other radios too! (Here is the next one.)

This radio is a precious gift from Piet Hoen.

The first time I saw the Radiomarelli 9A75 was in the window of an antique shoppe in Bologna, Italy. The shop was closed, but I went there four or five times to see if it would ever be open (the iterinary next to the door wasn't very reliable). A few hours before my departure I found the shop open and discovered that the radio was in questionnable shape and priced at 550.000 liras (about 300 ECU!). I left Italy with another radio.

A few months later Piet told me he had an old junker to give away; after seeing a picture of the above radio I immediately wrote him to say that the junker had found its new home. Under loud cheers to the honor of Piet the Radiomarelli 9A75E was added to my collection in February, 1997, but waited for a restoration until April, 1998.

Data for this radio
Type Radiomarelli 9A75E
Bands L (900-2000m), M (200-560m), C1 (31-53m),
C2 (19-32m).
Cabinet Wood and bakelite, 40x36x23 cm.
Tubes 12EA7GT (self-osc. mixer), 12NK7GT (IF),
12Q7GT (det+AF), 35L6GT (output),
35Z4GT (rectifier), 2 dial lights.
Controls Volume (pull for pickup), Off/tone, band, tune.
Produced Italy, 1946/47.
Paolo Borroni and Marco Berti sent me this Schema.

Technical Peculiarities

RF Section: The radio has four wavebands and is tuned inductively: that is, the tuning circuits consist of a fixed capacitor and a variable coil. The mixer tube is a pentagrid type and the IF tube should be 12NK7GT, but this tube was missing and I put a 12K7GT instead.
The dial lists some of the exotic places that are never received in the cold swamp called the Netherlands, and therefore never found on Philips dials: Jerusalem, Bayrouth, Cairo. Of course I cannot receive these stations (perhaps they don't exist anymore after half a century) but looking at the names already gives me a warm feeling and brings the memory of sipping cold drinks under palm trees.

AF Section: The loudspeaker has no permanent magnet but is of the field-coil type; the field coil serves also as the choke coil in the power supply, and by mounting the output transformer on the speaker one needs only three wires between the chassis and the speaker. Tonality control is by a three position switch that places zero, one, or two capacitors accross the output transformer's primary. The tonality switch is combined with the power switch.

Power Supply: The power transformer of this radio is an autotransformer; I cannot really see why this was chosen. With the autotransformer, the radio cannot be used with DC, while the chassis is still connected to the mains (the chassis is `hot'), thus the autotransformer combines the disadvantages of transformerless and transformer radios. The autotransformer has many taps so the mains voltage can be switched easily without the use of any dropping resistors (which would always run hot). The tube filaments are connected in a series string (150mA, American style), I think to keep the currents through the autotransformer small. The two dial lights are also connected in series, but are fed from a separate (14V) tap on the transformer. Plate voltage is obtained by half-wave rectifying the voltage on the 190V tap of the transformer. The filter capacitors (22 and 25 microFarad) are a little bit small compared to later standards, certainly for half-wave rectification, and the hum of the radio is definitely present (though not annoying).

The Cabinet: This is a real Italian `design' piece as you can see from the picture. Actually it is what makes the radio interesting, because the quality of the electrical design is questionnable. The cabinet has wood parts and aluminium sides in bended shapes which made me nickname the radio: `the radiator radio'. But perhaps the Italian designers didn't even know what a radiator heater was...

Gerard Tel, gerard@cs.uu.nl.