Dating fender amps transformer codes
The electrodes are attached to leads which pass through the envelope via an air tight seal.
On most tubes, the leads are designed to plug into a tube socket for easy replacement.
These are marked with EIA code “606” which is the company number for Schumacher.
Clearly Fender wasn’t afraid to use incorrect parts when they were in a bind. The 5G12 Concert is the earliest version from very late 1959 and early 1960 so the existence of a tweed example, while extremely rare, is certainly plausible since Fender was making lots of tweed amps during the same time period.