I know Google or similar should be my friend here, but struggling to find the right item.
I have a Gunson Superstrobe timing light for the car, but the ferrite ring on the HT pickup is cracked, so obviously doesn't work any more.
It's a square U shape and square cross section, as per the attached photos.
There is a sliding cover with a bar ferrite encapsulated to complete the magnetic circuit, and a coil round one leg of the U. I did try using a slice out of a round ferrite ring, but can't get it to work.
Anyone any thoughts for a supplier please?
I did contact Gunson, who put me in touch with their spares supplier, who in turn would only quote for a full replacement lead; Can't remember the exact price, but it was north of £50. 
The U shape is dimensioned as follows;
i.e. approx 6mm x section, 16.5mm high, & 25mm wide



Edited By peak4 on 18/03/2016 12:44:03