What do I need to know about isolation transformers?

[Ripthorn]

Hi guys, I have a submini tube preamp that works perfectly, but I wanted to create a bipolar power supply using the double half-wave rectification shown in RG's power supply basics article.  After hooking it up, I blew my bridge rectifier, and i think it was because I was grounding one of the windings for the bipolar supply while trying to use that same winding in the rectification process for the rest of the power to the preamp.  So i am thinking that an isolation transformer should do the trick, but I don't know what kind to get or what specs to pay attention to.  I was hoping this one at Radio Shack might work http://www.radioshack.com/product/index.jsp?productId=2103994&tab=summary, but I am wondering if the frequency response (300Hz-3 kHz) will make it a bad choice for the 60Hz AC that will be going through it.  Anyone have any advice or suggestions?

[gmoon]

If the back-to-back wallwart trick isn't for you, try searching for the "Triad N-68X" iso trannie.

Only about $12 USD. Allied and Mouser (among others) carry them.

[R.G.]

If you're willing to put another transformer in, just get a small 24Vct transformer and use it secondary to do the +/- power supply. Then there is no chance of interaction with the FWR 12V.