McMichael Twin Superhet from 1934

 
 This radio looks older than it really is and may help to explain why McMichael ran into financial trouble in 1934, however, under new leadership it recovered and went on for many years. Although looking dated it was, in fact, an up-to-date superhet receiver, but sadly did not have a dial that did it credit, as by 1934 many sets had large interesting dials marked with lots of continental stations.

 
 The case is veneered in walnut so will look good when treated with some proprietary scratch remover. The front speaker cloth is in dire need of replacement but that at the rear, hopefully will just need gluing back in place.

 

 You can't fail to notice the intriguing title and of course the picture of the front of the set where you can see two similar loudspeakers. The manufacturer's literature claimed the receiver had stereophonic sound, but that of course is not what we'd understand by the term today.

This set is one of only a few that uses a metal rectifier and thus perhaps saving a little on its Marconi Tax which by this date stipulated not "valves" but "valveholders" in order to stop sets being sold "less valves" with a box of the same supplied "under the counter" as it were.

 When I removed the two rear covers I found the upper one has a metal plate attached to prevent heat from the output valve from damaging the case. The lower cover has cloth which may be for improving air flow but probably to prevent things being poked into holes which would have been necessary if the usual perforated cover had been fitted. I say this because immediately behind the lower cover are positioned three high voltage components viz. a massive mains transformer, large metal HT rectifier and a block HT smoothing condenser carrying live termials on its top.

The set has two heavy metal chassis, the lower carrying the power supply has metal side plates.. for what purpose I wonder? Clearly manufacturing costs may well have been a trifle on the high side making the set expensive and perhaps not recouping all its development costs... remembering that manufacturers were obliged to bring out a new range of models every year in order to keep up with the high rate of progress of receivers and competitiveness.

Once I'd begun to remove the chassis from the case all became clear. First I was able to loosen the grubscrew on the remaining circular knob and having spotted the centre screw on the wavechange spindle the knob pulled off. The top chassis is completely rust free and is secured to the side panels screwed to the bottom chassis. The side panels are not separate pieces of metal but form the sides of the three sided structure also holding the pair of loudspeakers. Very convenient.

Below are views of the complete assembly.

The valves which have 4 volt heaters, apart from the first (behind the AC2 output valve) which has a later shaped glass envelope, look original and are from left to right :

AC/HL (B5 triode), AC2/PEN/DD (B7 pentode with something like 3.5 watts output), AC/VP1 (B7 variable mu pentode), AC/VP1 (B7 variable mu pentode), AC/TP (B9 triode-pentode frequency changer). No rectifier valve as the set uses a metal rectifier.

 
 I found a pair of aluminium sleeves loose in the cabinet. These fit over two of the valves. The coils, including the two IF transformers are enclosed in square aluminium cans whose upper halves just pull off for access. Note the early balloon-shaped frequency changer valve.

 
 

 
 There's evidence of servicing in the four missing screws (two either side) and lower down you'll see a Radiospares 47uF condenser.

 

 Unfortunately the dial is badly distorted and to fix this might mean removing it by drilling out the rivets holding it in place. The distortion probably arose because of the heat from the dial lamp. The local station must have been about 330m?

Later, I found that using a hair drier and some judicious prodding I was able to remove most of the dial distortion.

 

 Below, after a spot of heat treatment...
 

 

 

 Above is a "wet" electrolytic condenser which needs to be vertical when power is applied, in which case how does one access the underside of the chassis to make measurements?

Above right the Radiospares condenser and right the only part of the original speaker material was around the edge of the speaker aperture and not visible from the outside of the case and the torn black cloth is loudspeaker dust cover.

New grille cloth will need to be substantial in order to cover the hole without sagging because unlike most sets the speakers are not in contact with the cloth.

 

And below a set of labels from this set.. I'll swap these for better pictures later 

 

 

 

 

 Above, after reassembly with the new cloth in place.

 I'm on the lookout for a service manual or schematic to add to this page....

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