Looking at the layouts, the 18 watt and the 20 L&B seem to use the same power transformers.  Input can be 120 or 240V, and output is 290 or 3.15 V.  I'd rather not have a heavy transformer shipped from abroad, when I can get one in the US.  Looking at the Mojotone site, which is the distributor (I think) for the Heyboer transformers, they have a transformer for the 18 watt that has outputs of 290 (two of them) and 6.3 (one of them) volts.  Would this transformer work?  3.15 is half of 6.3, so maybe I'm just looking at the specs wrong.  If this won't work, can anyone recommend inexpensive but high quality transformers readily available in the US?  I'd rather not spend $ on a MM transformer.

As a second question, is it possible to build this amp as is, but with an additional jack to bypass the preamp, so that I can use other preamps with it?

Thanks