OP

Quoted from rufessor:

I have noted over the years that not all knockers are equal- seems that some are a shot gun blast that send people ducking on first hearing it and others are so weak I struggle to hear them when others are playing at the same time. I had cleaned switches, replaced coils, etc and finally decided my Williams grand prix was just never going to be loud...
I found these after seeing someone else suggest their use and after a few minutes with the soldering iron and addition of a diode (being strictly adherent to EMF principles) I now have a pretty loud knocker on my Williams. I did my gottliebs too- hoping to take them into the super loud category!
A little full wave DC rectifying at the coil goes a long way!!
Easy peasy- very satisfying, and now I get a
Real reward for a high score! A LOUD knock!!

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