Modifying to 220V operation. How to make sure?


Taking the bottom cover off my VTL MB100 I've noticed the extra set of isolated wires from the power transformer.
I called the manufacturer and they were not able to be clear since they do it usually as extra feature having an option to re-wire the unit to 220...240V operation.
There is some plan on how I plan to verify that the unit will operate at 240V and I want to discuss it.
1. Make sure that rectifying bridge is able to operate at 240V if not than I would have to replace it(or even upgrade).
2. Take off all tubes
3. Reconnect wires from the power transformer and turn on the amp into the 220V receptacle.
4. Check Cathode voltage from the tube sockets(Is it safe to run amp with no tubes? What issues am I facing here?)

If I need to replace bridge what parameters should I provide the manufacturer(of the bridge) becides input-output voltage and tolerance%?
128x128marakanetz

Showing 1 response by twl

Marakanetz, I am not familiar with your VTL, but in general, the transformer is the only issue you have to deal with. All rectification/regulation and everything else takes place after the secondary winding of the power transformer. The 110 to 220 change all takes place in the transformer. If there is a provision(set of wires on the tranny) that is intended to do this, then all you need to do is hook them up with a correct power cord with 220VAC plug. The current will be 1/2 of the current used at 110VAC. You don't even have to worry about getting the polarity wrong. But you have to be sure that these wires are made for that purpose. And you have to be sure that you use the right wires. The ones I have seen have 3 wires on the primary side. Leg A, Neutral, Leg B. When hooking up for 110VAC, you select a Leg(A or B) and neutral. When hooking up for 220VAC, you select Leg A and Leg B. Leaving the neutral out. Generally the colors for Leg A and Leg B are Red and Blue(but may vary), neutral is always white. Always connect the ground. If you can disconnect the secondary winding connections to the amp, then you can measure the output voltage of the tranny with a voltmeter while attached to 110VAC, and then change the primary wires to the 220VAC configuration as outlined above(at your own risk) and again measure the output voltage to see if you still get the correct voltage at the secondary outputs. This is what I have encountered, but it is up to you to verify what is correct for your gear. I find it hard to believe that the people at VTL couldn't tell you exactly what to do, unless they didn't want you in there messing around with it. Remember, this is high voltage stuff and is dangerous. If you have any hesitation, don't do it. You could hurt yourself, or the amp. Or even be killed.