09-10-2022, 09:39 PM
Today I spent four hours replacing a ball bearing.
In the pile of sets to be renovated or completely restored are a few cream Bush DAC90A radios. Unfortunately all have the small heat cracks over the dropper common with these sets.
Picking one at random, the selection was one that looked completely untouched, complete with the mains lead and the hallowed plug, good clear tuning glass scale, all undamaged knobs and an undamaged back.
A quick look around revealed that the drive cord was intact and moving the needle, the on/off volume control had a decent click but the wave change switch felt very odd, lacking end of travel stops and a bit crunchy feeling.
Making a start by taking the back and knobs off, filthy chassis out, all valves are in and no previous repairs seen. All waxy capacitors present along with much soot and thick black dust everywhere
The wave change switch is definitely broken, there is no detent ball bearing.
Connecting some power via the limiter initially, no bangs, no shorts, produced reception on long wave only even when positioning the switch carefully in the right place for medium wave. Cut the badly crumbled speaker wires to get the cabinet out of the way to safety.
To remove these switches is involved. The tuning spindle is in the way and two of the five wires on the switch are on top amongst the cord drive, difficult to get to without melting the cord.
The easy way I have found is to drop the spring off the hook on the tuning drum, slip the cord off the pulley at the other end of the needle slide and slip it off the tuning spindle. Then remove the chassis front to back brace, one locating stud and two 6BA nuts and bolts, remove the tuning spindle bracket, three 6BA nuts and bolts and front bearing plate, two more 6BA screws. This allows the switch to be removed from the bracket, which is slotted, unsoldering the five wires in the process.
Examining the switch, it has one crunched up contact finger which accounts for the lack of medium wave, and the brass ball retainer is bent out stopping the switch passing the tuning spindle, and sideways. Bit of a mangled mess. The ball is long gone of course. Checking I find I have some 4mm balls which would seem to be the size that will work.
Carefully reshaping the switch contact and the ball retainer allowed a new ball to be fitted. Not a quick job. Greased and oiled, the switch now works, the ball stops the spindle turning past the two end stops.
Just got to put it all back together, very fiddly with these nuts and bolts with grip washers, get the cord drive back on the spindle and pulleys, re-hooking the spring using a fishing line loop to pull it into place, sounds easy but it isn't. Remembered to solder the wires back on as the assembly was manoeuvred back into place.
New speaker wires fitted and powered up, it works fine on both wavebands. Not running it too long as those waxy caps will need to go.
Tidy up, four hours to do a simple but fiddly repair. Not even changed any capacitors yet, no wonder the radio and TV repair trade has gone.
In the pile of sets to be renovated or completely restored are a few cream Bush DAC90A radios. Unfortunately all have the small heat cracks over the dropper common with these sets.
Picking one at random, the selection was one that looked completely untouched, complete with the mains lead and the hallowed plug, good clear tuning glass scale, all undamaged knobs and an undamaged back.
A quick look around revealed that the drive cord was intact and moving the needle, the on/off volume control had a decent click but the wave change switch felt very odd, lacking end of travel stops and a bit crunchy feeling.
Making a start by taking the back and knobs off, filthy chassis out, all valves are in and no previous repairs seen. All waxy capacitors present along with much soot and thick black dust everywhere
The wave change switch is definitely broken, there is no detent ball bearing.
Connecting some power via the limiter initially, no bangs, no shorts, produced reception on long wave only even when positioning the switch carefully in the right place for medium wave. Cut the badly crumbled speaker wires to get the cabinet out of the way to safety.
To remove these switches is involved. The tuning spindle is in the way and two of the five wires on the switch are on top amongst the cord drive, difficult to get to without melting the cord.
The easy way I have found is to drop the spring off the hook on the tuning drum, slip the cord off the pulley at the other end of the needle slide and slip it off the tuning spindle. Then remove the chassis front to back brace, one locating stud and two 6BA nuts and bolts, remove the tuning spindle bracket, three 6BA nuts and bolts and front bearing plate, two more 6BA screws. This allows the switch to be removed from the bracket, which is slotted, unsoldering the five wires in the process.
Examining the switch, it has one crunched up contact finger which accounts for the lack of medium wave, and the brass ball retainer is bent out stopping the switch passing the tuning spindle, and sideways. Bit of a mangled mess. The ball is long gone of course. Checking I find I have some 4mm balls which would seem to be the size that will work.
Carefully reshaping the switch contact and the ball retainer allowed a new ball to be fitted. Not a quick job. Greased and oiled, the switch now works, the ball stops the spindle turning past the two end stops.
Just got to put it all back together, very fiddly with these nuts and bolts with grip washers, get the cord drive back on the spindle and pulleys, re-hooking the spring using a fishing line loop to pull it into place, sounds easy but it isn't. Remembered to solder the wires back on as the assembly was manoeuvred back into place.
New speaker wires fitted and powered up, it works fine on both wavebands. Not running it too long as those waxy caps will need to go.
Tidy up, four hours to do a simple but fiddly repair. Not even changed any capacitors yet, no wonder the radio and TV repair trade has gone.
Boater Sam.
