[Boatanchors] 51J's vs R-338's?

[Brian A Clarke]

Hi Al,
Thanks for the lead. Not a single 522 - number there at all - not even the
one that started my query.
I suspect the reason for this is that the item I have is called a Mechanical
Filter Plug-in Adapter Type No 353B-60. It looks like it is meant to replace
a normal B7G tube, perhaps near the end of an IF chain? Perhaps like the
Bill Orr article suggesting replacing a 6BA6 with a 6BE6. But for what
centre frequency?
73 de Brian, VK2GCE.