Marconiphone Model 253 table radio

serial No.253-352200
chassis No. 12100D


As received on the left and as restored and working on the right

Marconiphone model 253  Four valve Long and medium wave band AC mains operated table top valve radio housed in veneered wood case. Made in UK 1933

This radio was given to me in 2013 by Ian Rea. He rescued this one from the loft of his mother's house when she moved some years ago. As can be seen from the pictures it was in a poor condition but seemingly complete and unmodified. A penciled note on the chassis indicates that it was repaired in May 1945 but I could see no obvious repairs.  Several problems that would need fixing were immediately obvious when the chassis was removed from the case: A new rectifier valve would be needed, the HF amplifier valve would need repair, the loudspeaker cone would need support, the dial assembly would need re-stringing, the inter valve transformer and the metal can housing capacitors had overheated and leaked black pitch over the chassis. With all the valves removed I energised the set and checked the mains transformer, all seemed OK and the pilot lights worked. The loudspeaker produced a click from a 9 volt battery and the field winding and output transformer checked OK for continuity. A successful resurrection seemed possible! The other obvious  discrepancy was that the valves were all of Mullard manufacture rather than the Marconi ones specified (see specification lower down the page)

Chassis and speaker as received (note the broken rectifier and broken valve top cap)



The majority of the paper capacitors are housed in a wax and pitch filled tin plate box manufactured by Dubilier. The connections can be seen on this view of the underside of the chassis. The inter valve transformer together with two associated capacitors are housed in a pitch filled heavy cylindrical screening can. With some difficulty each was gently heated and the contents extricated. The transformer was OK but all the capacitors were discarded and replaced. The loudspeaker cone moved freely and the rotten flexible peripheral support was carefully scraped away and replaced with a piece of cotton fabric (from an old shirt) glued in place with PVA adhesive.  


Replacement capacitors wired ready prior to being held in place with hot melt glue and fixing in the tin plate container. The loudspeaker repair is not a thing of beauty but it won't be seen.



marconiphone253

As can be imagined getting the capacitor assembly out and back in place was not the easiest of tasks but went well without mishap. The transformer had me beaten for quite a while, I had muddled up the connections and one wire was making contact withe the screening can. Fortunately the wire on the top of the HF valve was long enough to solder an extension and re-attach the terminal which I super glued in place. With a replacement full wave rectifier and when attached to a fairly substantial aerial the set now works well, though some care is needed to tune weaker stations juggling between the volume/reaction and the tuning controls is necessary. The varnish on the veneered wooden case was in poor condition so I decided to strip it , apply a coat of stain  (American Walnut) and finish with Danish oil. The celluloid dial window was discarded and replaced with a piece of glass and a new piece of speaker grille cloth was glued in place. Finally four new felt feet were fixed to the base.


The brass screw operates in a similar way to the zero adjustment on a voltmeter.


These two labels are on the inside of the wooden cabinet


Picture from a 1933 catalogue


Original Specification

VOLTAGE RANGE 200 to 250 volts AC 50 to 60 Hz. This instrument is designed to work only on the voltages for which it is adjusted. Should any variation be experienced the supply company should be notified immediately.
IMPORTANT-This instrument must not be connected to a supply point which is "fused" for more than 5 amperes (working current).
CURRENT CONSUMPTION. 65 watts (approximately).
SPEECH OUTPUT 1.25 watts (approximately). 8 watts anode dissipation.
WAVELENGTH RANGE 200 to 550 metres (approximately) and 1000 to 2150 metres (approximately).

CIRCUIT DESCRIPTION.
Model 253 is a 3-tuned circuit band pass radio receiver with special aerial toppings which ensure the utmost degree of selectivity. The secondary of the band pass arrangement is connected to the grid of the
Screen Grid High Frequency Amplifier-Marconi MS4B. The sensitivity of this valve is controlled by variable resistance VR1 which is operated by the volume control knob.
Reaction Also coupled to the volume control knob is the variable condenser VC4 which controls the reaction coils L7 and L8. Choke (CK1) and condenser (C5) couple the M54B to the tuned grid coils (L5 and L6) of the
Detector Valve (Power Grid Type)-Marconi MH4.The detector valve is resistance capacity coupled to high ratio L.F. transformer, which Is in turn coupled to the
Output Valve (Pentode)-Marconi MPT4.- The transformer T3 (mounted on speaker) receives the output of the MPT 4 and transforms it for the speech coil of the electromagnetic moving coil speaker.
The high tension supply is derived from the
Rectifier (full Wave Type) Marconi U12