The Poor Man’s Variac

Properly known as a lamp limiter, this is an essential device for anyone thinking of repairing / restoring any vintage electronic equipment. It limits the amount of current that can flow into an appliance. This can help protect components from damage; in particular, capacitors which have not been charged for a long time. If there is a serious problem, the maximum amount of current that can flow into the set is whatever the lamp requires; about 180mA with a 40W lamp.

You Will Need:

  • 13 amp plug with 3 amp fuse
  • 13 amp trailing socket
  • 2 metres 1.0mm˛ 3-core flex
  • Batten lampholder
  • Piece of wood about 15cm. by 10cm.
  • Cable cleats
  • Selection of filament light bulbs (40W, 60W, 100W)

How to make it:
Fit the plug and socket to opposite ends of the flex (effectively making a rather short extension lead with only one socket on it). Using a sharp knife, carefully cut away about 10cm. of the outer insulation at the middle point, taking care not to damage the inner insulation. Cut the brown (live) wire, strip the two ends and connect them to the lampholder terminals. Leave the blue (neutral) and green/yellow (earth) wires. Screw the holder to a piece of wood (so the terminals are safely covered up), and fasten the wires to the wood with cleats.

How to use it:
Fit a 40W lamp in the holder. Plug the set into the limiter and the limiter into the mains. Switch on at the wall socket. The lamp should be off at this stage. Switch on the set (if the on-off switch and volume control are separate, make sure the volume is at minimum setting). The lamp should light up almost to full brightness, then go dim.

Note that a record player motor is unlikely to start from rest with a 40W lamp; it may well just bring the lamp to full brightness and sit there. If a gentle push does not help matters, then try a 60W or even a 100W lamp (remember it will get hot, so wear thick gloves when removing it).

Extra Note: If your ring main is not protected by an RCD, then you should connect the limiter to the mains using a “Power Breaker” type plug-in trip-switch. Also, it is considered polite to inform anyone working on a computer elsewhere in the house before you attempt any operation which may result in tripping — especially if you were hoping for any sympathy from them for the electric shock that precipitated the power failure!