You’ll find 2 rows of numbers, top set is the Fender part #, always starts with a 022, in this case it would be 022921. Works as follows, they have 6 numbers, first three is the EIA manufacturer, ignore this. A silverface made on the 23rd week of 1974 will have the same date code.The only good thing about dating amps this way is Fender never deviated-still valid today. If your JBL says D120F on it(look for the “f”) certainly could have been stock.I use this before buying a amp always-check all four transformers-will tell you if there has been problems along the way. On the bottom lower corner of the grill cloth was/is a 1×2 inch “JBL” plastic logo that Fender attached.By 1968 deluxes usually left with CTS/EMINANCE speakers (Jensen had closed down) Once in awhile you can see the EIA code, CTS-starts with a #137-sometimes these are under the doughnut fender speaker label.
The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air.
View the underside of the chassis (flashlight helps alot)look for the reverb driver trans.
Its in the middle of the 6 preamp tubes with the removable shields. For a black face, this transformer would have been made in 1964 during the 23 week (—423) The trick to this is they don’t renumber the decades.
A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts.
It consists of a minimum of two coils, the primary and the secondary, wound on the same core.
S.) and high power RF transmitters, as a display device in television sets and in microwave ovens.