For sale are two 6550 Tubes. These are marked "Amperex 6550 Made in USA". As far as I can tell, Amperex never made 6550 tubes. I Googled these and the consensus is that these are likely a Chinese-made. Just to clarify: These are most likely not Amperex brand, I think these are Chinese made. I tested them with an Eico 635 Tube Tester and they are in good shape, no shorts.