the little AC voltage switches

beat · « **on:** 1 Nov 2004, 08:43 pm »

Hey guys...and uh..gals?
I am at a loss here. I thought they shipped me the wrong amps..voltage wise. On the back next to the iec in, it reads 220v/50hz.."damn" I says. I ordered some step up trannys and the guy is reimbursing me.."cool" I says. Then I says "hmm, I wonder what it looks like under the hood" Very nice point to point job..decent caps... perfectly clean layout and oh..a little voltage switch! Now I dont know what to says?? Do I trust that switch so I can run 115, ditch the australian stock PC and swap power cords like a normal red blooded american audiophreakk?
thanks,
beat

JoshK · « **Reply #1 on:** 1 Nov 2004, 09:03 pm »

have a multimeter?

JoshK · « **Reply #2 on:** 1 Nov 2004, 09:10 pm »

I am sure you're alright to run it as you say but if you have a multimeter you can always test the voltages (carefully though!) to see if the tranny is stepping down to 115V.

beat · « **Reply #3 on:** 1 Nov 2004, 09:24 pm »

Oh,
you just made me think of something, Josh! I checked the resistance from hot to neutral with it in the 230 position and it bounced around 6.0 ohms. I switched it and it bounced around 2.0 ohms..I should be good to go, eh? Worst case scenario it gets too little voltage anyway right? better than the reverse, right?

JoshK · « **Reply #4 on:** 1 Nov 2004, 09:34 pm »

I have no idea what the relationship with resistance is in a transformer, I was talking about plugging the amp in with the case off. Be careful! Now turn the MM to measure AC voltage (the setting should be around 600V if your MM is standard) touch the black to ground and the red to the hot secondary of the transformer. This will give you the reading of the voltage.

Make sure you do not add yourself to the circuit when measuring or you will get a nasty shock.

JoshK · « **Reply #5 on:** 1 Nov 2004, 09:36 pm »

by the way, I learned all this myself just recently. I built my first preamp and I have been trying to coerce the voltages to their correct values so I had to learn how to measure the voltages.

beat · « **Reply #6 on:** 1 Nov 2004, 10:21 pm »

Cool,
I'll give it a shot. In my excitement I went and got the amps rigged in..well, long story short..the fuse popped. So i figured since I had already gone that far I just plugged my MB 100s in which I havent heard for a while so its cheering me up.
Thanks Josh

JoshK · « **Reply #7 on:** 1 Nov 2004, 10:40 pm »

Quote from: JoshK

I have no idea what the relationship with resistance is in a transformer, I was talking about plugging the amp in with the case off. Be careful! Now turn the MM to measure AC voltage (the setting should be around 600V if your MM is standard) touch the black to ground and the red to the hot secondary of the transformer. This will give you the reading of the voltage.

Make sure you do not add yourself to the circuit when measuring or you will get a nasty shock.

Actually I said this wrong....if the tranny is made for both voltages (220 and 115) with a switch then it will have two primaries, one for each voltage. But not different secondaries...duh.

OK, here is what you do. Plug in your amp into the step up tranny and measure the voltage on the secondary with the switch in the 220 position. This will give you the secondary voltage at 220 primary. Now if you really do have a second primary switched, then remove the step up. Plug the amp into 115, switch it to 115 and then remeasure the secondary. This secondary voltage should be the same as it was for 220. This is how you will know.

JoshK · « **Reply #8 on:** 1 Nov 2004, 10:41 pm »

P.S. the secondary is the hot wire(s) coming out of the tranny before the rectifier. Alternatively you can measure the B+ if you know where that is instead of the secondary for the whole process of comparing.