Edward Knobloch wrote:

I saw an article about a vacuum tube product detector circuit
which used no B+, the article appeared in Pop. Communications in 1998 or
so. I thought it might be an April fool article. Sorry, I didn't
save it for future reference.

73,
Ed Knobloch

Maybe it was an April Fool's article. Anything similar published
nowadays might be considered so given the going price for an unbothered
SX-28.

-Bill