Dating a vox amp
Ironically, this affects the resale value which is quite unfair because it probably means your amp is much more dependable and better sounding than an amp that's got all failing original components!
If you want an exact year, you could try the vintage guitar forum though I've not been there for a while so I don't know how active it is these days. Check this link out: The VOX Showroom - VSEL Vox AC-30 Top Boost Amplifier But then the larger vents came in the Birch-Stolec era, so your amp could be a transitional model - not the absence of bell covers for the speakers: there's always the possibility that the amp is one era and the cab speakers another, like you said.
People began to refer to these amplifiers as AC30TBs.
Later on, Vox also offered additional versions of the AC30 unit.
From what I can gather red mustard caps (known as "ketchups") were rather common occurance in 1965-66 so my guess would be around that for the innards. In the mid seventies I built six 50 watt versions of an AC30 in proper official Vox chassis & cabinets. Was working for a UK music shop at the time, so they definitely got out there in the wild.
About this time, the "Top Boost" (or "Brilliance") feature became available as Vox's optional addition of a rear panel-mounted circuit that introduced an extra gain stage and tone controls for bass and treble (as opposed to the single "tone" control of earlier AC30s).
The AC30/4 also carried over the AC15's preamplifier circuit, which included the EF86 pentode in its "Normal" channel.
Vox initially offered a 1×12" version but subsequently introduced the 2×12" AC30 Twin, which solved the volume problem at larger venues.
Yours has a few part substitutions - I don't think the Power transformer looks original (is that a date on it?
), and various caps and resistors have been replaced over the years.
Search for dating a vox amp:
It is known that it is the 'brilliant' model (or top boost) and it was Edge's earliest amp used to record every U2 album Since the higher output AC30/4 shared its preamplifier design with the lower powered AC15, Vox discovered the high-gain EF86 tube was susceptible to microphonics, or even failure, when exposed to the increased vibration present in this uprated amp.