The horn button on the R50 is well used and so when the horn failed to work, it was the natural suspect. However, in the process of elimination, I removed the horn and discovered that it produced no noise. Opening it up, the diaphram seemed fine and the adjustment screw worked, but neither helped to produce any sound when manipulated. Applying 12V rather than 6V did not awaken anything either. Resigned to getting a new horn, I tried a few bike shops and then ordered one online from Hucky’s . When it arrived I discovered that it had more modern blade terminals rather than the post terminals of the original, so I had to convert the wiring ends to suit. However, once all done, the horn now bleats as it should. On a 45 year old bike with 27HP and cable operated drum brakes, the horn is a significant safety device !!