It is cause for celebration any time a new $5 micro back 637 variety is found. Jim Hodgson recently acquired the top-grade Series of 1934A San Francisco Federal Reserve specimen from the LB block illustrated here. Series of 1934A 637s from any district are notoriously difficult to find, being among the rarest of the 637 varieties regardless of Federal Reserve district.
The purpose of this article is to provide an overview of what makes the $5 637 notes among the most avidly sought of all the small-size varieties. Back plate 637 had the most extraordinary life of any small size currency plate documented to date.
The number 637 is a plate serial number. Plate serial numbers are from a set of consecutive numbers for a specific type of plate, in this case, $5 backs. Plate serial numbers are the numbers inside the lower right border of notes.
In contrast, we also will be dealing with plate numbers, which are from a larger set of numbers that thread through all the plates regardless of denomination. The number 1442 is from the set for all back plates and is the number that was assigned to the plate that carried the notes bearing plate serial number 637. The plate number was printed only in the top border of the printed sheet and was trimmed away when the sheet was separated into notes.
The earliest stage of a plate made by electrolytic deposition is called a basso. The plate number is assigned to the basso, so both are the same and interchangeable. Molds created in the electrolytic process are called altos, which have their own numbers.
Collectors know plate 1442/637 by its plate serial number, so that number will be used throughout this discussion.
Plate 637 began life in 1935 as a master plate
