[sdiy] Weird 4072 in my 2600

[Doug Terrebonne]

Hi, I just got another 2600 and this one has a 4072 filter which I've never seen 
before - 


http://www.synthparts.com/my2600_4072.jpg

The 4072s I've seen look like this - 

http://www.retrosynth.com/gear/arp2600/my_early_tonus/4072/2600_early_tonus_4072_003.jpg



As you can see the one in my 2600 is a longer board with a totally different 
layout. It is dated 1975 and says it is fab 4072-003. Anyone seen on like this? 
Is mine maybe a very early (maybe prototype) version? This 2600 is the last 
version (model 2601) grey-face right before the black/orange model.

Doug 
synthparts.com