Fender pro junior dating
Fender does provide some guidance for dating their modern amps....
that information can be found here."All Fender amplifiers manufactured from 1990 to the present include a date code, printed on the quality assurance (QA) sticker on the back of the amp chassis.
The 12AU7 has even lower internal resistance than the 12AT7 and even less gain (20 percent of a 12AX7). The 12AU7 is designed to deliver buckets of current, not a beautiful preamplified signal.
So stick to the 12AX7, 5751, and 12AY7 for your preamp.
They only delay the onset of distortion and limit the total amount of distortion.
12AX7: Clean range ends at 4 5751: Clean range ends at 5 12AY7: Clean range ends at 7 So the effect of these lower-gain tubes is to expand the clean headroom across more of the volume control’s range.
It’s the preamp tube that Fender used in classic amplifiers such as the Tweed Deluxe, many Champs, and the revered 57 Twin. After that, the 12AX7 starts producing serious amounts of distortion. The 5751 or 12AY7 don’t give you any more clean headroom.
These measurements were made with the Fender-specified 1KHz input signal at 50m V, roughly equivalent to a fairly hot guitar being run wide open tone/vol.
When the THD (total harmonic distortion) goes over 5 percent, you start hearing the distortion.
This black-and-silver sticker contains several lines for "sign-offs" on completion of sound and electrical testing.
The final line contains a date code of two printed or handwritten letters denoting the amplifier's production date by year (the first letter) and month (the second letter)."You need to find the Black and Silver Sticker...