[Radioroslyn]

Yup those new '37 models have those the self centering tubes (aka octals) '36 model use the older standard base tubes. On the 5Y4 vs 5Y3 I think you'll find in the socket that there are no receptacles for the tube pins come in contact with, they have been deleted. You have to use a 5Y4 or a 5Y3 w/an adapter. The 37-61 is an up dated version of the older model 60 that started back in '33. Edited previous post to reflect proper tube pins.