Thanks for everyone's help, I didn't really want to add a second identical transformer because it's a heavy transformer, and I wanted the radio to retain it's portability. However, 25.2V RMS is a much higher voltage than I need. The power supply itself is designed to disable battery charging if the voltage or current is not high enough, so as long as the rectified voltage is at least 4V above 18V DC (that's what the battery charger needs to charge properly), so a 17.25V RMS transformer will work properly.
If I consider the maximum current draw of all the components of the unit (there are a lot of them), then I end up with current draws like this:
1.) Radio; draws about 500mA nominally, spikes at roughly 700mA during start up.
2.) VU meter; by far the least efficient, x4 60dB displays totaling 80 LEDs @ 5-10mA a piece, will total 800mA. Then Throw in the draw of the ICs will total about 1A (that's where all the power is going)
3.) FM/AM transmitter; this only draws a maximum of 350mA
4.) iPod charger; iPods are supposed to charge at 500mA, but when I measured it was only 350mA even when it was pushed to as much power as possible (Brightness at max, volume at max, playing a movie, etc.)
5.) Thermal management; this is to help the unit stay cool if it gets too hot, and warm if it's too cold (the radio is ancient and it has temper tantrums if it's pushed too far). This draws about 200mA with the fan on, and about 600 to 800mA with the heater (depending on wheather I use a 20 ohm or 30 ohm power resistor).
6.) The power supply itself; thermal control in the power supply is more efficient than thermal control for the entire unit, only about 300mA maximum, The battery charger works at 700mA at it's peak, and the "power switches" (a bunch of CMOS F-F) draws about 200mA. I'm trying to lower this by switching to TTL F-F, and ditching transistors for MOSFETs.
So everything totals about 4.2A of current, any ideas on how to lower this draw would be appreciated, or if you know of a transformer that meets the power requirements, but isn't the size of a small house, that works to.
Thanks, Vince