Dating cts speakers
The larger amplifiers are quite unique for that time period, with the 3000 series using 6 6L6 tubes (Fender didn’t do this until the late 70s with the Super Twin), and the 4000 series with 4 6550, and the monstrous 8000 with 6 8417 power tubes inside.
long as nothing is plugged into the output jacks, you should be fine.
And if the buzzing doesn't travel with the speaker, there's a good chance the buzzing is coming from something else and not that speaker...like a separation between the plywood's laminations, for example. As tubes age, their internal components loosen a bit and can rattle.To check this, isolate the head from the cab by putting the head on the floor or putting something between the head and the cab, like foam or a folded blanket.I pulled this information from Google's cache of the site.
It has a note at the top of the page that they were reprinting with permission from the authors of Ampeg: The Story Behind the Sound, ©1999, published by Hal Leonard.
Together they command a masterful experience with every drive. The CTS was tested and fine-tuned on Germany’s famed Nürburgring racetrack.