Customer repairs: HMV receivers

HMV Model 1375, S/No. 2102; Repair No. 22

Reported fault: Makes noises when playing
Fault diagnosis: The fault is typical of an internal short in the output valve. During testing this proved to be the case.
There were a few other faults noted. Firstly the output valve grid coupling capacitor was leaky - this may have precipitated the fault in the valve as its effect was to put a high voltage onto the grid electrode. Secondly the negative feedback link between the output circuit and the loudspeaker transformer was found to be disconnected and thirdly the mains on/off switch on the tone control is lazy and needed adjustment and lubrication.

Repair: A large quantity of dust was removed from the interior of the radio and the tuning mechanism, which was seized, cleaned of sticky deposits and old oil.
The tone control carrying the on/off switch was removed and dismantled. The switch mechanism was lubricated and the activating parts adjusted to ensure reliable operation. When the switch worked reliably it was re-assembled and the tone control refitted.
The leaky output stage grid coupling capacitor was replaced.
The loose negative feedback link was reconnected and a new UL84 fitted.
The radio was re-assembled and satisfactorily tested.
The dial pointer needs to be refitted.

Parts fitted:- UL84; coupling capacitor

HMV Model 1643 Radiogram, Repair No. 37

Reported fault: Cartridge needs stylus replacing
Diagnosis: The old stylus had been removed from the cartridge and it was difficult to see how it went back together.

Repair: The original parts were reassembled then the new stylus was fitted.

Note: The radio dial was seized in one direction and the volume was a little on the low side. The volume and tone controls were noisy. Repair suggested at future date.

HMV Model 1121, S/No A14 109361; Repair No. 1455

Description: The radio is in especially good condition and retains all its original features although I have replaced the mains lead with one having modern brown and blue wires.
This model is unusual in covering the "trawler band", the frequencies between medium waves as well as the standard short wave broadcast band. Wavelengths covered are as follows:-

Long waves.....2000m to 720m
Medium waves....580m to 187m
Short wave 1....187m to 50m
Short wave 2.....50m to 16m

The dial illumination is novel. The dial assembly is tilted so it can be read without difficulty in normal lighting, or alternatively, through an edge lighting system using the glass plates as lightguides. The paint used was probably luminous when new, containing a radioactive isotope, but over the years this has faded somewhat. The tilted glass also provides another feature in that it allows openings for the much larger than average loudspeaker used in the set. As the speaker is sited behind the dial it re-uses the dial space rather than requiring a second area of front panel as with contemporary sets.

As with all non-VHF radio sets of this vintage one needs an aerial. Positioning and size of an aerial is not critical unless it is used in the vicinity of television sets which unfortunately generate lots of interference. Fluorescent lights may also generate interference. With this model the aerial need only be a few yards long. If interference is a problem the earth socket, at the rear, could be connected to a convenient waterpipe or similar having a path to ground. This often improves matters. The tone control can be used to minimise whistles from interfering TV sets.

I changed the audio output valve, which had an intermittent heater, but the condition of the other valves is excellent. With old valve radios the coupling capacitor, used to connect the audio to the output valve, must be replaced as it invariably develops a leak, placing a positive bias on the grid of the audio output valve which considerably shortens its life. Although the set works perfectly at the moment, in use the odd component may fail because of its age. Remember that valve sets take a few minutes to warm up and come on. If the set ever fails to come on, and after a couple of minutes there's no healthy crackle when turning the wavechange switch, turn it off, wait a few minutes and try again. It may be due to an old capacitor reforming and taking time to become active.

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