Hi, this is my first post. I've been lurking on here for years and soaking up a ton of great info, so a big thanks to all the contributors! Now to my question...

First, I'm brand new to the site, I have read some of the fine threads and it all looks good. I'm recently retired, had a medium sized Music store for a long time. Lots of tube gear still around.

Specifically> I own an Ampex 351 with 2 amplifers and this box which is labeled

Does anyone know how to tell the difference between an Ampex 350 vs a 351? A friend of mine has a couple of these Ampex pres, and from pictures i've found it obviously one or the other, but there is nothing on either of them to distinguish which model it is. Any help is greatly appreciated.