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 2 responses by bob_bundus

I like the idea of first removing the tubes for safety's sake, seems like a very good idea. When you power up, try measuring the filament voltage at a tube socket. If you get twice the reading that you expect then you're probably applying the 240V to a unit actually wired for 120V. If you get the correct filament voltage (may be slightly high because there's no filaments loading the transformer output) then it appears you're already setup for 240V. Cathode & anode voltages could vary significantly, especially with no tubes in the circuit; it's hard to say what you should expect to see there.
Herman's cautions regarding popping caps are certainly valid. Try powering it up on a variac at half-voltage first, making the measurements as planned.