This page deals with the dreaded subject of drive cords and tuning systems.


A typical early tuning system where the tuning capacitor is driven by a "disc" system....no drive cord.



Rear view of the same system.

DRIVE CORD SYSTEMS



Here we see a Murphy chassis which employs a standard drive cord system. Notice the pulleys at the top of the dial,these must be free turning otherwise it could damage the cord and cause a strain on the tuning capacitor bearings. When re-stringing drive cords it is very helpful to have the service data in front of you,this often has a drive cord diagram included.



This is a Bush chassis which employs a drive cord system. Notice the wavechange switch has a drive cord system to change the waveband pointer.

It has got to be said that the drive cord renewal has got to be one of the most feared jobs to undertake by the radio engineer/technician. I too have been driven to the point of tears with some makes of radio most notably Philips. On reading a book by Chas E. Miller he describes Philips drive cords down to a tee. He is dead right they are a nightmare,they make the other brands look easy. Most drive cord systems thankfully are mounted on the radio chassis,and can be withdrawn completely and be re-strung out of the chassis. Some Philips radios are not like this however,and the act of withdrawing the chassis without paying proper attention will cause the drive cord to snap causing tears,cursing and ultimately lots of man hours re-stringing unecessarily. This is because the pulleys are mounted on the cabinet and need to be undone before extracting the chassis. PLEASE NOTE I DO POSSESS QUITE A NUMBER OF CIRCUIT DIAGRAMS AND MAY BE ABLE TO HELP YOU WITH A DIAL DRIVE PROBLEM. PLEASE CONTACT ME VIA THE CONTACT PAGE STATING THE MAKE OF RADIO AND MODEL. I COULD ALWAYS PUT A PICTURE OF YOUR TUNING DRIVE DIAGRAM ON MY WEBSITE FOR YOU.

REPLACING A BROKEN DRIVE CORD

First of all,IF THE DRIVE CORD IS SNAPPED BUT STILL IN PLACE DONT PULL IT OFF,MAKE A DRAWING FIRST NOTING WHICH DIRECTION THE CORD IS WOUND AND HOW MANY TURNS ROUND THE SHAFT,DONT PUT TOO MANY TURNS ON THE SHAFT IT WONT STOP THE CORD SLIPPING. IT WILL CAUSE THE CORD TO RIDE UP THE SHAFT AND CAUSE POSSIBLE SEIZURE.

1.Determine first which way the tuning pointer has to move(when the tuning capacitor is closed,the pointer must be at the low frequency part of the dial).

2.Feed the new drive cord through the hole in the drum.

3.Tie the end of the cord to the spring.

4.Now the hard part. Feed the drive cord through the various pulleys and spindle,how it goes depends on the make of radio,but you can usually work it out given time. If you have the circuit it should be a doddle. Also if you were lucky enough to have a snapped drive cord that was still in place,this should be easier to work out.

5.Feed the other end of the cord through the drum in the opposite direction to the cord coming out of it.

6.Tie this end to the spring.

7 Make sure that the pointer is travelling in the correct direction,or you will have to do it all over again.....oh no!!!!

EXAMPLES OF SOME DRIVE CORD SYSTEMS.


PYE P78


DEFIANT AF21


BUSH DAC11


BUSH DAC10


MARCONI 289,289A,296,298,HMV 442,443,570,570A