Potadyne A39 valve radio

Portadyne model A39 AC table top 3 waveband valve radio housed in polished wood veneered cabinet. Valve lineup TX4, VP4B, TD4A, A70D and rectifier. UK 1939/40

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I was given this radio which had been in his loft for several years by Kevin Greenlees who said it worked but the tuning mechanism needed attention. It turns out that he was right, but being cautious I checked the insulation between the transformer and chassis then removed all the valves, checked the mains lead and energised the radio via my variable transformer to discover that the dial lamps came on and nothing untoward happened. I then applied a gradually increased DC voltage to the main electrolytic capacitors monitoring the current drawn with an Avometer. Whilst thin was proceeding I dusted down the chassis cleaned the valves and applied switch cleaner to their sockets. When the reforming current drawn by the electrolytics had steadied out  I replaced the four main valves (but not the rectifier), connected an aerial, plugged the radio into the mains and gradually increased the HT voltage from my DC supply. As advised the radio came to life on all three wavebands, a promising start.

The cabinet appeared free from woodworm but needed a good clean and polish, the speaker cloth was very worn and fragile, the cloth covering the openings in the back panel was torn and also needed replacing. The thin 3ply of the back panel needed reglueing and strengthening. The rubber cores of the loudspeaker lead were brittle and perished and it was thought desirable to replace the mains lead with a 3 core one and earth the chassis. Fortunately the tuning drive mechanism is very simple and the broken cords were still in place so I was able to measure the required replacement lengths (two lengths in parallel) and feed them through the chassis and into the grooves on the drive shaft. The loudspeaker had been shrouded in a black dustcover since 1939 was in good condition and relatively dust free.

The underside of the chassis revealed that the main electrolytic had been replaced at some time in the past and three other capacitors which checked out OK had been replaced. The volume control is clearly not original either. The one over heated resistor is a puzzle, it measures 1.5K and runs cold when the set is energised, the fault which caused this overheating in the past has clearly been rectified.

Four views showing condition as received (note that some components had been replaced}