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Vox AC-30 question

3/28/2000 8:13 AM
Craig D
Vox AC-30 question
Hello all.  
I was curious to know what circuit is considered the "classic" Vox AC-30 sound. I remember a post not that long back that suggested the early ones had a pentode pre-amp similar to an AC-15.  
I have a few schems from the vox website, but wasn't sure what was considered "the" AC-30.  
Any opinions?  
3/28/2000 8:49 AM

I´ve tried some Voxes, and I even own and old original Vox AC-30 Top Boost with celestions. I won´t say mine is the perfect example of a "classic" AC-30, it´s a question of tastes.  
But some other people opinions some of them amp collectors, the AC-30 with original Top Boost (not retrofit) with Mullards ECC83, GZ34...and Blue or Silver Celestions (it´s said they are the same, just the paint is different) is what can be considered a classic AC30.
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3/28/2000 5:05 PM
Ted Breaux

Vintage AC30s come in different flavors, and many people just aren't aware of this. The very first, the AC30/4 is the original AC30 which started the craze. This is the AC30 which uses the EF86 pentode. This amp is very gainy, and gave the Shadows their famous sound. Only the very earliest AC30s have this circuit, have black control panels, and have only 4 inputs (2-channels). IMO, these are the best sounding AC30s, period. As for the familiar red panel AC30s that followed, they came in three models, "Bass", "Normal", and "Treble". You can determine which a particular amp is by looking for a single letter (B, N, or T) stamped next to "AC30" or the serial number on the serial plate. Also, if you remove the back panel of the amp, you'll usually see the word Bass, Normal, or Treble written in orange, on the chassis, right under the power switch. These amps all sound like ac30s, but sound different as per their designations. The Bass models are bassy, the Normal models are more 'natural' sounding, and the Treble models are trebly. Also, the three different brands of transformers used in these amps tend to give different twists to the sound as well. Since these amps use 12AX7s and have three channels, some gain was sacrificed, and when the complaints came, the add-on top boost circuit was invented. Sometime in what seems like late '64, the top boost became standard, and these amps have both a Bass and Treble knob on the control panel, as opposed to just a "Tone" control. There are separate schematics for each model AC30 which clearly show the minor differences which differentiate each model  
If you are planning on building an AC30, obviously I recommend the very early circuit. If you intend to build or buy a vintage model, be advised that if you want a non-top boost amp, the Treble models will be the most flexible. The Normal models sound a little muffled without top boost, but as far as top-boosted amps go, I think the Normals sound nicest overall, with the Treble models being very vintage and trebly sounding. Of course, these amps just aren't right without the incredible, important low wattage alnico speakers.
3/28/2000 6:49 PM

Great stuff Ted!  
Is there a web site with the various iterations posted?
3/28/2000 7:17 PM
Ted Breaux

Not to my knowledge. A vintage AC30 buyer's guide might make an interesting web page. I only know these things because I've owned a slew of vintage AC30s. There are schematics for the Bass and Normal models in Pittman's Tube Amp Book, as well as the top-boost and reverb add-ons. Schematics for the Treble and EF86 (AC30/4) models can be had from Since the different versions are due to minor variations (mostly cap values) Anyone who decides to build an AC30 can easily check out the different versions (except for the EF86 unit). A new book by Jim Elyea will provide much more insight to Vox amps than "The Vox Story" did. Finally, the current Korg repros are actually a cross between the Normal and Treble circuit. This is clever in that it gives the best of both. Of course, they got the filter capacitance wrong!
3/29/2000 6:04 AM

There is some info and a bunch of downloadable schems over at:  
3/29/2000 2:21 PM
Ted Breaux

The "Normal" and "Bass" schematics are there, as well as the top-boost add-on. Absent are the "Treble" and EF86 model schematics.
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