McMichael 371 - UK Vintage Radio Repair and Restoration Discussion Forum

jim_beacon · 20th Oct 2005, 9:45 pm

Hi,

I've just finished repairing a McMichael 371 for a colleague, and although it has not been used for 50 years, it required very little work.

The set is a short superhet, using Mazda 7 pin valves, built around the end of 1936. It is housed in a largish wooden cabinet, and has a "beam of light" type pointer, with a different colour for each of the three wavebands.

I had to replace the normal paper and electrolytic caps (all leaky), though none of the resistors needed replacing. Most of the wiring is cotton covered, and was OK, but the rubber covered wiring to the dial lamps (two permanently on, and three switched by the wave change switch) had to be replaced - a scrap computer PSU yielded a number of lengths of the correct colour and gauge of wire. The mains lead was also replaced.

After the usually insulation checks, the set powered up fine, and produced 5Live and Talk sport with out an aerial connected - on those grounds I decided re-alignment wasn't needed!

The set has an unusual tuning drive, the capacitor has a geared reduction, driven by a large drum (about 7" diameter). The drum is driven from the tuning knob spindle via a continuous fabric belt (about 3/16" wide), with a springe loaded jockey pulley to tension it. There are no multiple turns around any of the pulleys. The fabric belt is in poor condition, and has temporarily been replaced by a length of plastic-covered lacing cord (it works very well!).

I intend to have the set back on the bench in a week or two for a further check over - this is mainly due to the poor original construction of the set - many of the joints are made up of three or four wires laid on top of each other and soldered, there is no atempt to make a sound mechanical joint. I expect trouble from these after nearly 70 years!

All in all, I've put in about 6 hours work on the set, and am surprised by how little work was needed!

Jim.

20th Oct 2005, 9:45 pm	#1
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	McMichael 371 Hi, I've just finished repairing a McMichael 371 for a colleague, and although it has not been used for 50 years, it required very little work. The set is a short superhet, using Mazda 7 pin valves, built around the end of 1936. It is housed in a largish wooden cabinet, and has a "beam of light" type pointer, with a different colour for each of the three wavebands. I had to replace the normal paper and electrolytic caps (all leaky), though none of the resistors needed replacing. Most of the wiring is cotton covered, and was OK, but the rubber covered wiring to the dial lamps (two permanently on, and three switched by the wave change switch) had to be replaced - a scrap computer PSU yielded a number of lengths of the correct colour and gauge of wire. The mains lead was also replaced. After the usually insulation checks, the set powered up fine, and produced 5Live and Talk sport with out an aerial connected - on those grounds I decided re-alignment wasn't needed! The set has an unusual tuning drive, the capacitor has a geared reduction, driven by a large drum (about 7" diameter). The drum is driven from the tuning knob spindle via a continuous fabric belt (about 3/16" wide), with a springe loaded jockey pulley to tension it. There are no multiple turns around any of the pulleys. The fabric belt is in poor condition, and has temporarily been replaced by a length of plastic-covered lacing cord (it works very well!). I intend to have the set back on the bench in a week or two for a further check over - this is mainly due to the poor original construction of the set - many of the joints are made up of three or four wires laid on top of each other and soldered, there is no atempt to make a sound mechanical joint. I expect trouble from these after nearly 70 years! All in all, I've put in about 6 hours work on the set, and am surprised by how little work was needed! Jim.