Safety Test
Hi, I have a Metaxas Preamp that I am sending to Paris and need to tap the transformer for 220V. It has a seperate power supply and when I opened it there are two bundles of wires for the primary each consisting of a Black, Brown and Orange wire. As it is wired now for 110v it uses the Black and Brown on one bundle. When I measured the resistance it showed 7.6 Ohms. I was told that the 220v taps should measure almost double as they will be in series. I measured the Black and Brown from the other bundle and it also measured 7.6 Ohms. The Black and the Orange from the non used bundle measured 9.4 Ohms, the Brown and Orange on this bundle measured 2.1 Ohms. Would the 9.4 Ohm measurement be the 220v tap? I have a Variac but it only goes to 140v. Is there anything else I can do to verify I have the right taps. Thanks in advance.
Ron
This procedure should not result in human injury or property damage, if
executed responsibly. Measure and note the voltage of one of the
transformer secondaries, while in place, running on 110v setting, plugged
into a normal outlet. Carefully change the transformer wiring to 220v.
Using a safely constructed test adapter, connect a light bulb of similar
watt rating to nameplate wattage rating of your preamp, in series with the
incoming power. If the rewiring to 220v is correct, your previously
measured secondary should have about half the voltage it had before,
while testing on 120v. Testing at half voltage to get a voltage reading,
then promptly turning the preamp off, should not harm it. Improper wiring
will almost always cause the bulb to brightly light, limiting incoming current
to protect your transformer. A properly wired and insulated test fixture is a
must! I keep one in my toolbox and it has been a valuable safety and
troubleshooting aid that has kept me out of trouble many times!
