All i know is one is newer than the other but thats it. What do they do and whats the difference?.  Ive bought a 1980 series 1 and wondered which electronics will it have and what is the newer one doing differently.

As I understand it, the older electronics are just fine unless you are getting RF interference.  There is a lot more RF around today than back then.  It seems that each instrument and each locale is different.  Neither my '76 Series I MSG, nor my '77 Series I LSG 12 string exhibits the interference problem.  Accordingly, I have not had them upgraded.  Wolf's  (Sonicus) recently purchased #33 bass picked up the RF interference in the studio where he bought it, but doesn't have the problem in my studio or other places.
 
Hope this helps.
 
Bill, tgo

I'll be reading this too... PF-5 was replaced by PF-6 pretty early on, (1974-75??) but I always wondered what the difference between the two was.  
 
If I understand correctly, with the PF-5 set the trimpots are accessible from the front of the instrument rather than the backplate. Also the battery box was located between the pickups where the hum-cancellers later went.

The last PF-5 is 73'-047 SSB, the first PF-6 is 74'-048 SSG.
 
Eiji

Hello Friends ,  Bill tells the story above as well !  
Yes , ___I love my PF-5 electronics # 73-32 . I recently played her at a coffee house type gig  and she sounded great and remained quite RF /EMI noise wise.  The rehearsal studio where I first met her was another story where  she displayed noise &  and proudly presented several  RF transmissions simultaneously . Nonetheless it was love at first sight and we left together with her previous protectors blessing ,  I was a lucky man !  
 
Wolf

I'm wondering if there is any difference in the input impedance or anything like that. It occurs to me that I am currently using pickups that were most likely designed around PF5 electronics, but I have a PF6 board. I get noise sometimes.