When I recorded in studio 2 at Abbey Road a few years ago, one of the most amazing things in a day full of amazing thing was playing bass through their RS124 compressors. These compressors have been detailed thoroughly in Brain Kahew's excellent "Recording The Beatles" book. I can tell you first hand, it's a magical sounding compressor if you like McCartney's bass sound. You can hear me playing through the Abbey Road one here: www.corinashley.com
(the video at the bottom).
A few years back, I found a busted up old Altec 436B in an electronics repair shop and bought it. It sat under my bed for at least 5 years until I found someone who could do an approximation of the Abbey Road mod. Only a few people really know for certain what the engineers at EMI did to these back in the day, but an LA based engineer named Bryce Gonsalez seems to have gotten pretty close.
Here's my first attempt at just running my Hofner through it. Normally, I'd be combining this with a mic'd up tube amp and recording to tape, but I'm pretty happy with this as a start.