While I'm in the process of modding / rebuilding some Vox amps, I thought I might try the original Vox AC-4 from 1962, or at least a simplified version of it.
Apart from the simplicity, I want to try something with an EF86 pentode valve as the preamp. These were in a lot of early Vox amps, but they were more difficult to manage than an ECC83 as they are a bit microphonic, and this became a problem as wattages increased. Less of a problem in a small amp like this - but still needs to be managed.
I have not detailed the wiring of valves, resistor wattages, cap voltages and transformers etc on my layout, as you can work this out from the schematic - and if you can't work it out, you should not be playing inside amps.
The output transformer will be a Hammond 125CSE, with larger secondary options - who wants a 3 ohm output these days? And I will most likely be using something bigger than an 8" speaker - but you never know, I might find something cool and vintage that will change my mind about this. Might meed to increase the cap value on the EL84 cathode, as a larger speaker might show a lack of bass with a 22u.
Not sure if I will stick with the valve rectifier or go silicon - I'm leaning towards valve.
VOX AC-4 SCHEMATIC - TREMOLO CIRCUIT REMOVED
MODDED AC-4 LAYOUT
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