The HMV 456 is a small wooden mantle radio covering the AM broadcast band. It has three valves plus a rectifier, so it was intended for a city high signal strength environment. It has a dial scale showing the radio stations for Australian states, which was driven by a single TUNING knob for selecting the desired station. The VOLUME control is one the right, and a TONE control switch is on the left. There is a clear plastic sheet on the front to provide the labels for the knobs.

The valves are all octal types, using a 6A8 as the mixer, a 6G8 providing the IF amplifier, detector, and AVC function, and an EL3 as the audio power amplifier. The rectifier is a 5Y3. It looks strange, as the EL3 is huge, and the 5Y3 is a small GT size. The radio has no ferrite rod aerial, but provides and AERIAL and EARTH terminal for an external aerial. The 6 inch speaker is an electro dynamic type, and has the speaker transformer mounted on it. There is a lead and plug for the speaker, which mates with a chassis socket, so it is easy to remove the chassis from the cabinet.

It has a plated steel chassis, with fibre octal sockets. The radio chassis only uses two thirds of the cabinet space. The tuning capacitor and coils are on a separate small chassis, mounted on the main chassis.

The radio looked in very good condition, the wooden case just needed a polish, as there was no damage. The chassis was removed from the case, and the dust brushed off. The power cord was stiff and not flexible, so it was replaced with a new cloth covered cord. The radio was plugged into a VARIAC and brought up to full voltage slowly. The radio showed no signs of life at all. I checked with the multimeter, but there was no heater voltage or HT voltage.

The power transformer had a burnt smell, and checks showed an open circuit primary. It was a small transformer, and I appeared to have nothing the correct size. I asked at an local radio meeting but nothing was available. I asked about having it rewound, but was told it would be expensive. I eventually found a transformer in my spare parts bin, tested it on the bench, then fitted it to the chassis. It powered the valve heaters for an hour before it started to hum and then overheat. It was too much of a coincidence for two transformers to fail, so I spent a day looking for short circuits. There were none that I could find. Maybe I had two faulty transformers! I began looking through old chassis in the parts pile. I discovered an old piece of test equipment, that had the correct size transformer, so I removed it, and powered it up, on the bench with nothing connected to the secondaries. This one ran for two days with no problems. I then fitted it to the radio. I wired up the heaters, plugged in the valves, and ran it for another two days. The transformer only warmed up a little. I disconnected the electrolytic capacitors in the radio, tacked in some new ones, plugged in the 5Y3, and applied power. Some HT appeared and there were sounds from the speaker. A weak station was able to be tuned in.

I checked the resistors and all were good, with only a few high in value, and those were in non critical parts of the circuit. The rubber wiring was hard and the insulation cracked off when they were disturbed. Some rubber wire was taken from an old mains cable that had good flexible rubber wires inside. The hard wires were replaced, one by one. The wiring to the power transformer was tidied up and insulated. The dial lamps were replaced. The volume control was crackly, and then failed. It was replaced with a working old one that looked the same.

The mica capacitors were left alone. The four electrolytics were removed, gutted and fitted with new electrolytics inside. Three were HT and one was a cathode bypass. They were wired in and the radio tested again. All appeared to work. The ten paper capacitors were removed, gutted and stuffed with new/old Philips polyester capacitors. They were fitted and the radio tested, then an alignment was performed.

This was a lot of work, but the under chassis views show that it looks very close to original. No one else knows, and probably no one will ever see the under chassis again, (but I know). The radio performs well, for a city environment radio. It was unusual to have two transformers fail.

Ray Robinson