Here's some info (and a modification) on a new Ampeg that I purchased in December of 2007, an Ampeg SVT-VR. The "VR' stands for Vintage Reissue. While it is not an exact duplicate of the original SVT, the circuit is basically the same, and this amp actually sounds identical to my other two vintage original SVT's ( a '69 and a '75). Many people believe that the USA VR's are better than the ones that were made in Vietnam, but I disagree completely. In fact, I have found that the fit and finish on the Vietnam ones to be better than the USA ones. The components, at least on mine, are the same identical components and all of the transformers and PCBs have "SLM" either labeled, or silk-screened on them. Over the past 35 years, I have owned no less than 12 SVT's, and I have found every one of them to be a great amp. It is my opinion that if an SVT doesn't sound good or doesn't have enough power, then something is wrong with it and it should be serviced.
My SVT-VR sounded great right out of the box, but since I have alot of NOS Amperex, Mullard and RCA preamp tubes (12AX7A's and 12AU7's), I did a little tube rolling and got it to sound even better. It now is a bit smoother and fuller sounding with the NOS preamp tubes, as opposed to the five Electro Harmonix preamp tubes that came in it.
Here's a pic of my three SVT's (top to bottom-2007 SVT-VR, 1969 SVT, 1975 SVT)
The only feature that I don't like in the new VR is that it has a relay-timer circuit on the standby switch. I tested this circuit with my trusty US NAVY variac and found that if the amp sees any less than 112 volts AC, it will NOT come out of the standby mode. Or even worse, if you are playing somewhere and the voltage drops below the 112 volts, it will automatically go into the standby mode, and the green panel lamp will turn to red. This only happened to me once on a gig that had questionable AC, but once was enough for me so I decided to do something about it- bypass the relay circuit altogether and have a "manual" standby, just like on the originals. Its a really simple modification if you're a tech and even if you're not, as there is no soldering involved, and the mod is completely reversible.
A word of warning: If you are not familiar with the extremely high and lethal voltages in a tube amp, DO NOT perform this mod yourself, unless the filter capacitors have been fully discharged!)
Okay, on to the actual modification............................................
If you look at the schematic of the AC power supply pcb, you'll see that the standby switch is connected to J26.
(click on the image below to open a larger version)
The easiest way to do this is to make a "Y" cord that will just make the necessary connections: It will have to have two males and one female:
Here's a picture of the AC PCB. A yellow wire that comes from the standby switch is connected to J26. Carefully pull off this connector and plug it into one of the males on the "Y" cord.
Then, do the same thing with connector J27 (pull it off and connect it to the other male on the "Y" cord).
Now, connect the female of the "Y" cord to the J27 terminal on the PCB.
It's a good idea to use a couple of wire ties to secure the "Y" cord.
And that's it! it really couldn't be easier. I tested the amp with the modification and my SVT-VR will now operate on the same AC voltages as a vintage one. I used my variac and ran mine on only 95 volts to make sure that it wouldn't go into the standby mode, and although, with the lower voltage, it had a bit less power, it worked perfectly, and the panel's pilot light stays green even on 95 volts. So there you have it, an extremely simple mod to make sure that your SVT-VR will operate well under the required 112 volts. Just be sure to use the standby properly. I always allow the amp to warm up at least 1 minute before I flip it out of standby. This allows the tube's heaters to warm up before applying the high voltage (B+) to them.
thanks for looking at my Ampeg SVT-VR page.
SVT-VR with SVT410HLF cabinetSVT-VR with SVT610HLF cabinet SVT-VR with SVT810-AV cabinet