13-07-2019, 02:12 PM
Ever a sucker for a challenge, I acquired a Murphy U102 radio.
Produced in 1946 when there must have been terrible shortages of materials and possibly of pre-war design.
Its built like a tank, heavy steel frames around a vertical chassis. Necessity being the mother of Invention, there was a shortage of pots with mains switches, the back of the volume control is open where the switch should have been! Instead there is a DP toggle switch operated by a lever on the spindle.
Thick bakelite cabinet has suffered in that all 4 chassis corner securing studs have broken out, 3 missing completely. Otherwise no damage, needs the white repainting.
I've looked it over carefully and can see no repairs at all, it looks to be totally original, Sprague capacitors and all. Original Mazda Octal series heater valves, 200mA chain, all in place. Even the dial lamp works.
I don't particularly enjoy AC/DC sets but this had a 3 core mains lead ( unfortunately cut off) with the earth wander plugged into the earth socket at the rear. There is a capacitor between here and the chassis, will need a Y type replacement.
Running it up, it needed the electrolytics slowly brought back to life, so it spent an hour on the isolation transformer feeding the variac feeding the lamp limiter just in case.
A wax capacitor across the rectifier started to cook so I removed it, the cap across the mains, metal can, is holding so far, X type needed.
Rectifier valve seems reluctant to provide a full HT so a 1N4007 diode was connected across it to prevent the valve suffering if the capacitors failed.
Changed the output valve grid capacitor, it was leaking a volt or so, not bad for a 73 year old Sprague.
Gave it time to slowly come to life.
And it works! Quite well really considering. Well worth saving.
If I can find a way to restuff the metal can Sprague capacitors I think it will be worth the effort to preserve the originality.
Produced in 1946 when there must have been terrible shortages of materials and possibly of pre-war design.
Its built like a tank, heavy steel frames around a vertical chassis. Necessity being the mother of Invention, there was a shortage of pots with mains switches, the back of the volume control is open where the switch should have been! Instead there is a DP toggle switch operated by a lever on the spindle.
Thick bakelite cabinet has suffered in that all 4 chassis corner securing studs have broken out, 3 missing completely. Otherwise no damage, needs the white repainting.
I've looked it over carefully and can see no repairs at all, it looks to be totally original, Sprague capacitors and all. Original Mazda Octal series heater valves, 200mA chain, all in place. Even the dial lamp works.
I don't particularly enjoy AC/DC sets but this had a 3 core mains lead ( unfortunately cut off) with the earth wander plugged into the earth socket at the rear. There is a capacitor between here and the chassis, will need a Y type replacement.
Running it up, it needed the electrolytics slowly brought back to life, so it spent an hour on the isolation transformer feeding the variac feeding the lamp limiter just in case.
A wax capacitor across the rectifier started to cook so I removed it, the cap across the mains, metal can, is holding so far, X type needed.
Rectifier valve seems reluctant to provide a full HT so a 1N4007 diode was connected across it to prevent the valve suffering if the capacitors failed.
Changed the output valve grid capacitor, it was leaking a volt or so, not bad for a 73 year old Sprague.
Gave it time to slowly come to life.
And it works! Quite well really considering. Well worth saving.
If I can find a way to restuff the metal can Sprague capacitors I think it will be worth the effort to preserve the originality.
Boater Sam.
