Valve identification

[Hacksawbob]

Hi I have this valve which I'm trying to identify. 

I bought a JJ Tesla ecc83 from Watford valves a while back , but I don't think it's that as there is no red writing on it.  Which means it might have come out of the Hartke   LH500 which I leant to @D0gS0litud3 

Any ideas?

Has a little radar dish shaped thing inside on top, 

Letters I can make out are

U3S1B

And

503

[Hacksawbob]

never mind I think I have found it. 

 

[Reggaebass]

I did look out of curiosity, but couldn’t find anything , glad you found it