Quoted from KenLayton:For those with early solid state games from Williams, Gottlieb, and Bally which use a 6 inch full range speaker, they have been hard to find at times. I've found an excellent replacement at Newark (formerly MCM Electronics).
Ken, I have quite a few Gottlieb, Bally and Williams early SS pins. The speakers all appear to be original and work. Is it worth $6.00 to replace these speakers in your opinion? Is the fidelity and clarity a little better or a lot better? I like to keep original parts on my restorations, but good sound is important enough to spend a few bucks on if they are noticeably better.
Mr. Layton, I want you to know that you are one of my favorite posters. You are knowledgeable and always willing to share your expertise here on Pinside. 
If it is a KenLayton post, then I know that it will be worthwhile!
