Hi Jahn; great tone! For those who might not know, this is how the Weber, or any other, volume atttenuator works. The attenuator allows the amp to be turned up inducing distortion in the preamp / output tubes, damped back down - without messing up the signal - and put back into the speaker. Result; the sound of an amp screaming along at 9/10 on the volume dial but at pain-free, room-level volume.
Source: Weber VST
FWIW: any easily-distorted late 50s/early 60s twin 6V6 amp will more or less sound like Jahn's without an attenuator because, unlike the Princeton and many other highly-regarded Fender models, these 'brown' amps break up at 4/5, about the limit of room-level volume. Attenuators are widely used by players wanting to record, wanting the distortion, but unable to tolerate 9/10 volume to get it.