Hi every one

I recently brought myself a BIG nice, non working Tannoy SR 840, it’s in ok condition BUT I’ve come across a mod that I can’t find any info on
There seems to be 2 sockets for tubes, what’s even stranger is the fact it looks factory fitted - it’s dosent look like a amateur job(to my eyes anyway)

- Has anyone ever heard of this ore even better, any first hand experience with this mod?

I’ve previously had great feedback on old Tannoy gear in here, so I’m optimistic, there is someone in here with the experience/ know how

Bonus info: I’m Boeing to send it off to a local radio mechanic shop, whom excels in vintage gear…

Thanks up front for your time