Nos Tubes

Hi Folks.
I picked up some NOS tubes and as I'm not all that clued up on NOS tubes I wouldn't mind some opinions.
a few are labled RCA 5751.Are these actual RCA tubes as I do know a fair bit of rebranding went on.They have black plates and a code of 61/52.They do sound lovely.
One is an Amperex.Is this the famous Bugle Boy that I hear about?Any help is much appreciated.
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