Marconiphone III (M3) ReceiverSPECIFICATIONS
Model: Marconiphone M3
Type: TRF (Neutrodyne)
Made by: The Marconi Wireless Telegraph Co. of Canada, Montreal.
Frequency Range: Broadcast band
Tube lineup: Five UV-201A
Circa: First production 1924
Original price: $300 .
Comment: The Marconiphone III was a completely original development of the Marconi Wireless Telegraph Co. of Canada.
In the 1920’s, when the Canadian Department of the Interior held a literary contest for all of Canada called “Forests Protection” it was supported by the most important Canadian newspapers of the time. The prize was to be a high quality radio receiver. Not wanting to award just any receiver, the existing receivers of the time were evaluated and the Marconiphone III was selected as the best of the lot.
This receiver was an original development of the Canadian Marconi Wireless Telegraph Company of Canada. It employed six UV-201A vacuum tubes when production was first started. There are three RF amplifier stages ahead of the detector and two AF stages after the detector. The receiver is of the neutrodyne design and incorporates a special “bridge circuit”, a design patented by Canadian Marconi. No details about the bridge are available at this time.
The sensitivity of the neutrodyne design allowed the listener to tune very distant stations and eliminated any RF emissions from the set. For best results, Marconi recommended that an external loop antenna be used with the receiver although a wire antenna could be used as well. Interference from local stations or static could be minimized or eliminated by rotating the loop antenna.
In 1924, the base price of the radio was $250. Fitted with tubes , A and B batteries and Splitdorf earphones, the price jumped to $345. If inflation is taken into account (over 1000% since 1924) then the equivalent cost of fully accessorized receiver would be around $3,400 in 2008.
FRONT PANEL MARKINGS
(Note: Serial 442 does not apply to any of the featured radios in this document)
MFG. PLATE ON INSIDE BACK: 'THE MARCONI/ WIRELESS TELEGRAPH CO./ OF CANADA LIMITED/ MONTREAL/ PATENTED1918-23-24/ TYPE NO. M3 SERIAL NO. 442'/ 2 CARDS ON INSIDE BACK: 'Diagram of B Battery Connections for/ MARCONIPHONE III./ [DIAGRAM]' 'MARCONIPHONE 111/ NEUTRAGENERATIVE RECEIVER/ CALIBRATION CHART [SEE SUPP.INFOM FOR COPY]'/ DESIGNATIONS ON KNOBS: 'AERIAL' 'LOOP' 'LOOP/EARTH' '6 VO[?]S/+' 'DETECTOR' 'BALANCE' 'AMPLIFIERS' 'BALANCE' 'AMPLIFIERS' 'PRIMARY/ TUNE' 'R.F./ TUNE' 'DETECTOR' 'BATTERY/ SWITCH' 'AMPLIFIER'/ ON FRONT PANEL: 'MARCONIPHONE III/ NEUTRAGENERATIVE RECEIVER/ MARCONI/ CANADA'
THEORY OF OPERATION
Wikipedia provides this explanation of the neutrodyne receiver.
"The Neutrodyne was a particular type of Tuned Radio Frequency (TRF) radio receiver, in which the instability-causing inter-electrode capacitance of the triode RF tubes is cancelled out or "neutralized". In most designs, a small extra winding on each of the RF amplifiers' tuned anode coils was used to generate a small out-of-phase signal, which could be adjusted by special variable trim capacitors. This would cancel out any stray signal coupled to the grid via plate-to-grid capacitance.
The circuit was developed in the early 1920's by Alan Hazeltine and used by a group of more than 20 manufacturers that were licensed to produce Hazeltine-Neutrodyne receivers, This group was known as the Independent Radio Manufacturers. Hazeltine's invention effectively neutralized the high-pitched squeals that had plagued early radio sets. The design also neutralized the stranglehold that RCA then held on the commercial radio industry. Compared to the technically superior superheterodyne, the neutrodyne was cheaper to build and operate, and much easier for non-technical owners to use.
To properly set up a Neutrodyne receiver, not only did the circuitry need to be aligned for peak performance, (that is, getting all its tuned circuits operating "in step"), it also had to be neutralized. However, this procedure only needed to be done once (usually by a serviceman) and thereafter the radio could be tuned by anyone without special skill, a unique feature at the time. The neutrodyne was the first commercial receiver suited to use by the general public. By 1927 some ten million of these receivers had been sold to consumers in North America".
|The Marconiphone M3 was provisioned with a loop antenna but it could also be used with an external wire antenna. The example of this receiver held by Le Musée Québecois de la Radio is a 1924 model. This image was derived from a brocuhure which described the set. (Image via Le Musée Québecois de la Radio)|
THE NEUTRALIZATION TECHNIQUE
Wikipedia also describes the neutralization technique. To neutralize a Neutrodyne receiver, the procedure went something like this:
- Turn the receiver on. Tune the receiver to a strong station near the high end of the dial (e.g., 1500
kHz) or use a modulated signal generator set to that frequency and tune the receiver to it.
- Turn the receiver off.
- Start with the final RF stage and work backwards towards the antenna.
- Disable the tube filament (so the tube is not conducting) either by unsoldering one lead and taping
the wire to prevent it from shorting to anything or (preferred) using a neutralizing adapter between
the tube and its socket.
- Turn the receiver on. If you can hear the signal that the receiver is tuned to, that tube needs
- Adjust the neutralizing capacitor for that tube for minimum volume.
- Retune the receiver for maximum volume.
- Adjust the neutralizing capacitor for that tube for minimum volume.
- Turn the receiver off.
- If you disabled the filament by unsoldering it, resolder the lead.
- Repeat with each tube until all RF stages have been neutralized.
- The receiver should be realigned after being neutralized and if it still squeals the neutralization
- It is important to neutralize using the actual tube that will be in that socket as grid-plate
capacitance varies some from tube to tube. Also once neutralized the tubes should not be
exchanged between sockets. Often replacing a defective tube with a new one required
neutralizing the receiver again therefore tube replacement usually required a serviceman.
Type: UV-201A receiving
|The metal base version of the UV-201 tube. (Courtesy Radiomuseum.org)|
The power consumption of the tungsten filaments of tubes like UV 201 was very high, resulting in a short duration of the A-battery (filament battery). Tungsten filaments needed to reach high temperatures like incandescent lamps. They emitted a bright shining light when operating. As a result, they were called "bright emitters".
In 1922 an improvement was made. For metallurgical reasons (prevention of crystalization) the tungsten used in the filaments of incandescent lamps was mixed with a small percentage (some 0.7%) of thoria, a process patented by Westinghouse in 1910. It was observed that tubes with these filaments sometimes had a very high electron emission even at lower temperatures. The special process steps which produced this high electron emission were investigated and improved. As a result the thoria percentage increased to about 1.4%. The new design was called the thoriated tungsten filament or "dull emitter", because the required temperature now was lower, giving a dull yellow light. In this way, the power consumption was reduced to less than one half.
In 1922, Marconi UK formed the "Marconiphone" department, to design, manufacture and sell domestic receiving equipment. This equipment complied with Post Office specifications and tests, and was therefore awarded the BBC authorization stamp; initially sets were made at the Chelmsford Works. In December 1923, the 'Marconiphone' department was formed as a subsidiary of the Marconi Company. It would therefore appear, that in the UK, the name Marconiphone was applied to a division of the Marconi company but in Canada Marconiphone was applied as a specific product brand name.
In December 1929, the Marconiphone division was sold to the Gramophone Company, along with the right to use the trademark "Marconiphone" and the copyright signature "G. Marconi" on domestic receivers. The Marconi Company never re-entered the domestic radio market. In 1931, the Gramophone Company became Electric and Musical Industries (EMI) and produced domestic and radio receivers using the Marconiphone trademark until 1956, when receivers were made by the British Radio Corporation, under licence. Domestic receivers bearing the Marconiphone trademark produced after 1929 had no connection with the Marconi (UK) Company.
To see a list of Canadian broadcast band stations that were active in September 1923, please select this link. Courtesy Radio Station Treasury. These stations operated on wavelengths of 450 to 400 metres which put them between 666 and 749 KHz respectively.
|Front of receiver.|
|Back of receiver with cover down. Note that the dial calibration chart is affixed to the inside of the receiver, a rather odd place by today's thinking.|
|Rear view of chassis.|
|Filament power posts.||Aerial, loop and ground posts.|
|Dial calibration chart|
|Nameplate. Note the Marconi designation of M3.|
|Cover of operating manual||Title page of the operating manual published in French.|
|All photos in this table by Jacques Hamel. This Marconiphone III is the property of Le Musée de la Civilisation du Québec (Quebec City) and is part of their "Joseph Cardin Collection". Mr Cardin had been the local radio station (CJSO) engineer from 1945-6 to the end of the 1980's when he retired. Le Musée Québecois de la Radio also acquired a number of pieces from his estate after he passed away in January 2001.|
Contributors and Credits:
1) Le Musée Québecois de la Radio - Jacques Hamel, VE2DJQ
3) UV201 photo http://www.radiomuseum.org/tubes/tube_uv201a.html
5) The Proliferation of Tube Types http://18.104.22.168/portal/cms_docs_iportals/iportals/aboutus/ history_center/conferences/che2004/Goerth.pdf
6) French-only marketing pamphlet describing the Marconiphone III.
7) Radio Station Treasury 1900-1946 by Tom Kneitel. 1986. CRB Research, Commack NY.