Most people assume that the difference is in four versus two output tubes, and heavier transformers for the big version.
Also, people refer to the V-4 often as a 120W amp, and the V-2 as 60 Watts. Figures, no?
The trick is in the voltages. For some reason, the V-2/VT-40 have 50 extra volts coming off the rectifier. 545 Volts for the V-4, and 595 for the V-2.
The V-4 is actually a true 100W amp (100W RMS with all tolerances off to the worst case scenario) meaning that it will pump out MINIMUM of 100W. (Not like the sissy Fender watts, where 100 theoretical is more like 80 in reality!)
The V-2 does the same at 60W RMS. When you relieve a V-4 of two output tubes, with correct impedance it delivers 50W. The V-2, thanks to those extra 50volts, delivers 20% more.
WHY Ampeg did this remains a mystery to me. Fact is, it makes the amp sound different. To my ears, the V-2 distorts much earlier than the V-4 (even a V-4 with only 2 output tubes). The entire amp (pre-amp, tone circuit, everything) runs on higher voltage. A much more sensitive amp.
THIS IS ALSO why you can run modern tubes in V4/VT22's, but in the VT40/V2 they may fry.
One last word: These Ampegs were made for serious 70's musicians. I've played hundreds and hundreds of gigs on them, and they sounded great, WHEN PUSHED. I still play my V-2 rig, with a power attentuator nowadays to please the new generation of volume-shy club owners and listeners. You HAVE to bring it to distortion naturally (no pedals, no master volumes).
Those were the great unwashed smoking rocking (and everything else!) days....
