30-01-2015, 12:43 AM
If the noise is present at all settings of the volume control, then surely that implies that the audio stages are the problem?
Sure, the AF11x transistors grow tin whiskers, and might be responsible for the weak FM, but tackle one problem at a time...
My experience is that OCxx audio transistors are pretty reliable, but do check them by substitution if possible. Then, suspect any carbon composition resistors that are reasonably early on in the signal chain. Of course, it helps to have access to another example of the set, so that you can compare the noise levels...
If the FM performance is still weak after "treating" the AF11x transistors, you might need to try a line-up. If that fails to improve things, it might just be that the set is working as well as it ever did. Early FM sets were often a lot less sensitive than modern ones - especially UK-made ones in my experience. Sadly, Bush didn't quote sensitivity levels in the service manual, so it's hard to be more specific in this particular case.
Sure, the AF11x transistors grow tin whiskers, and might be responsible for the weak FM, but tackle one problem at a time...
My experience is that OCxx audio transistors are pretty reliable, but do check them by substitution if possible. Then, suspect any carbon composition resistors that are reasonably early on in the signal chain. Of course, it helps to have access to another example of the set, so that you can compare the noise levels...
If the FM performance is still weak after "treating" the AF11x transistors, you might need to try a line-up. If that fails to improve things, it might just be that the set is working as well as it ever did. Early FM sets were often a lot less sensitive than modern ones - especially UK-made ones in my experience. Sadly, Bush didn't quote sensitivity levels in the service manual, so it's hard to be more specific in this particular case.
