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VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Healing R401E/S401E Mantel Radio A. G. Healing of Melbourne made radios and TV sets for many years. They varied from quite simple units to reasonably elaborate ones. They never appeared to strive for the top end of the market, being content to stick with good, middle of the market equipment. The 401E 4-valver is a basic little mantel receiver de­ signed for areas where signals are reasonably strong. It is quite an attractive little unit in a brown Bakelite case, with the speaker grille on the left and the dial on the right. The dial has “Golden Voice” in its centre which was part of Healing’s trademark. It has two controls, volume and tuning. It has no on/off switch, the wall switch being required to do the job. It could be considered a miniature mantel receiver, although some sets of the era (1948) were smaller. The above-chassis view is filled with components, except for the power transformer and rectifier valve which are recessed below the chassis. It appears that provision was made to have a card type cover for the back, for other sets using this cabinet. This model apparently didn’t have a back, as the spots where the cover would The simple design of this Healing set extended to the gold-painted dial drum with the pointer printed directly onto it. 84  Silicon Chip have attached to the cabinet had never been drilled to take securing screws. Consequently, the set is easily removed from its cabinet, by undoing two screws along the bottom edge of the chassis at the back and taking the two knobs off. The set is then slid out of the cabinet but like many small radios, the dial scale and speaker remain in the cabinet. This makes it awkward so I length­ened the speaker leads, so that I could more easily service the set without having to remove the speaker from the cabinet. The dial light is also attached to the cabinet via a slip-in socket but it is easily removed. For a long life, the dial light runs from a 4.5V tap on the 6.3V filament winding of the power transformer. One interesting little point – there is a spigot protruding from the inside of the front of the cabinet that acts as a locating pin for the chassis. It stops the chassis from moving around inside the cabinet, seeing as it is only held in place by two screws at the back. The dial drive consists of a drum driven from a rubber grommet drive via dial cord. The grommet is a tight fit over the brass tuning shaft. The dial drum is a gold colour and there is a straight black line painted across it to act as the “pointer”. This is elegantly simple and works very effectively. The two operational controls are fitted the opposite way to normal, with the tuning control on the left and the volume control on the right. They could easily be swapped around, and maybe some sets were built with the controls arranged in the conventional manner. I am not a fan of deep chassis construction such as this example. Relatively speaking, it is not too deep at 55mm but being a narrow chassis, www.siliconchip.com.au Fig.1: simplicity is the keynote of this 4-valve super­het made by A. G. Healing. Not shown on this circuit is the filter choke which has its frame connected to the HT rail. care is needed in accessing some points. Some manufacturers seemed to believe that a deep chassis gave them the right to put layer upon layer of components in, just to keep things nice and compact. Pity the poor person who had to service the sets. Hot filter choke The filter choke is hidden underneath the chassis and just as well. It is mounted on an insulated fibre board and its frame is connected to the high tension (HT) line. This was done to minimise the voltage between the winding and the frame. This technique was used to help prevent electrolysis eating through the winding at some spot. Speaker transformers of this era were quite prone to the primary winding going open circuit and were often mounted so that the transformer frame was at HT too. Howev­er, this is the first time I’ve seen it used with a filter choke. The circuit shown has a dropping resistor instead of a choke, so it would appear that various modifications were done to the model throughout its production life. Servicing the 401E Being such a simple receiver, it is not hard to get it up and running. Most www.siliconchip.com.au paper capacitors were replaced as they were most likely leaky. The only ones I considered essential to re­place were C3, C11 and C13. However, the circuit is remarkably tolerant of slightly leaky capacitors in all locations. This cannot be said of many other receivers. All resistors bar one were within tolerance. The electrolytic capacitors were changed and a new 3-core power cord was fitted and a clamp attached to secure it in place. Knotting the power cable to prevent it being pulled out of the chassis is not an approved method these days. So if you do replace a mains cable, clamp it to the chassis with a metal or plastic clamp; it keeps the authorities happier. Having replaced the components most likely to give trouble (paper capacitors in particular), a resistor and the mains cord to the set, it was time to give it a go. I went through my usual Hiding under the chassis, adjacent to the 4.7µF 500VW capacitor, is the filter choke with its frame tied to the HT. This could give a nasty shock to the unsuspecting repairer. September 2001  85 These rear views of the set show how the power transformer is recessed right into the deep chassis. procedure of checking for any shorts in the power transformer, across the high tension line to earth and that the speaker trans­former had continuity in the primary winding. All was well. Power was connected and the set warmed up but its perfor­mance was not good. I do have a few replacement valves and by the nature of the problem and measurement of the cathode to earth voltage on the 6V6GT, it was obvious all was not well. The vol­ tage was not the designed 12V, so a replacement was tried. The set then 86  Silicon Chip sounded a lot healthier. Other than the alignment nothing else needed attention. Alignment The set is quite easily aligned. As the circuit has no automatic gain control (AGC), all adjustments can be done for maximum volume out of the speaker, provided you have a signal generator. If you have no signal generator, the best method is to connect a digital multimeter (DMM), set to a low voltage DC range, across R6 the detector load. A normal analog (moving coil) multimeter will unfortunately load the circuit too much and the readings are not likely to deflect the pointer sufficiently up the scale. Connect a reasonable aerial to the set. Tune to a strong radio station and with a small screwdriver, adjust the primary and secondary windings of the IF transformers L3 and L4 for maxi­mum reading on the meter. The volume control setting will affect the readings on the meter. You may not have the IF tuned to 455kHz but it should be close unless someone has been twiddling the adjustments. This is the easy part of the job. The alignment of the oscillator and aerial circuits is a little more complex. Place the chassis back into the cabinet and make sure that when the gang is closed, the black pointer line lines up square through the Healing name. If it doesn’t, adjust the drum on the gang spindle until it does. With the set in the cabinet, tune to a strong station that you know around 600kHz. If you are fortunate, the station will come in on the appropriate station marker on the dial. If not, put the dial on the station mark on the dial and withdraw the chassis from the cabinet. Now adjust C7 until the station coincides with the dial marking. All being well, you’ll be able to get the station tuned in accurately. Then adjust the core in L1 for maximum reading on the meter. The next step is to tune to a station around 1500kHz that you can easily recognise and once again, having identified the station, turn the dial until the correct station identification has the dial pointer behind it. Note: a few years ago, some sta­tions changed their frequencies and the markings on the dial may not be anywhere near where they were in times gone by. For exam­ple, 3NE moved from 1600kHz to 1566kHz, so older dial scales are no longer accurate. Leave the dial pointer coinciding with the station dial marking. Adjust C4 to hear the station, then adjust C1 for maximum volume and meter reading. The adjustments of the aerial and oscillator circuits interact with one another from one end of the dial to the other. Hence it will be necessary to go over the adjustments a couple of times to get the alignment as close as is practical. Having to slide the chassis in www.siliconchip.com.au Photo Gallery: Astor OZ “Mickey Mouse” Looking for an old valve? or a new valve? BUYING - SELLING - TRADING Australasia's biggest selection Also valve audio & guitar amp. books SSAE DL size for CATALOGUE Manufactured by Radio Corporation Pty Ltd in 1934, the Astor Model OZ “Mickey Mouse” was housed in an attractive veneered wooden cabinet and was the first of a long series of small sets to carry the “Mickey Mouse” and, later, “Mickey” name. The circuit was a straight 5-valve superheter­ odyne with an IF (intermediate frequency) of 455kHz and included the following valves: 6A7 frequency changer; 6D6 IF amplifier; 6B7 detector, AVC rectifier and audio amplifier; 43 audio output stage; and 25Z5 rectifier. The set was fitted with a 5-inch electrodynamic loudspeaker. A feature of this unit is its low HT voltage – just 130V – hence the choice of a type 43 output valve. This gave cooler running in the small cabinet. Photo Gallery: Astor “Mickey Grand” ELECTRONIC VALVE & TUBE COMPANY PO Box 487 Drysdale, Victoria 3222. Tel: (03) 5257 2297; Fax: (03) 5257 1773 Mob: 0417 143 167; email: evatco<at>mira.net Premises at: 76 Bluff Road, St Leonards, Vic 3223 been completely maladjusted, it is unlikely that this simple method will achieve the results necessary to get optimum performance out of the set. In fact, if the alignment is way off, you may not be able to hear any signals from the set. This can be compounded if there are defective valves in the set too. How does it operate Manufactured by Radio Corporation Pty Ltd in 1935, the Astor Model MZ “Mickey Grand” was housed in an attractive mini-console cabinet measuring just 380mm high. It used the same basic 5-valve super­het­ er­o­dyne chassis as the “Mickey Mouse” but was fitted with a larger loudspeaker (6-inch vs. 5-inch). As with the “Mickey Mouse”, this set also operated with an IF of 455kHz and a HT voltage of just 130V. and out of the cabinet to do this job is a real drag, but there is no alternative when the dial scale is attached to the cabinet. Once this procedure has been comwww.siliconchip.com.au pleted, it is desirable to seal the cores and trimmer screws with some plastic cement or nail polish to stop them shifting out of adjustment. If the tuned circuit adjustments have The performance of small 4-valve radios is never expected to be marvellous. However, many do surprise me and the performance of this little set is very good, rivalling a number of 5-valve sets. Obviously, Healing got the design of their coils and IF transformers close to optimum, to obtain the performance it does have. There is no AGC so it is necessary to adjust the volume control as you tune across the band, as strong stations will blast you and weak ones require the volume control to be advanced for reasonable volume. A set like this would not be good in areas where radio signals fade up and down due to this lack of AGC. However, it is designed for strong signal areas so this is prob­ SC ably not a great deficiency. September 2001  87