thanks for your help. I found the documentation the previous owner
did, and he used half of a 6sn7 in replacement of the 6j5 bfo tube and
labeled it an "inf. imp. detector. what would be the advantage of
doing this?
Also, Johns sx-28 restoration (and others) are the most incredible
restorations i have ever seen documented. Thanks for the links!
I've got a working sx-28 on loan to help in comparing/restoring mine.