I need a phono preamp (for a high output moving coil cartridge) that will fit in the back of a cabinet and be inacessible once installed behind a MacIntosh preamp. It cannot be more than 12 inches wide, 10 inches deep and 6 inches high. The smaller the better. It goes with an SME 10, JBL Paragon and MacIntosh Amps and Preamp. Any suggestions?
See if this one will work for you.It's really small.
Try a Dynavector or Parasound zPhono.

Check out the JLTi. Not only is it smaller than your dimensions, it offers 40/60 or 40/55 dB gain (depending on version) and it will compare sonically with units costing 2-3 times its price.
ZYX Artisan, if you are looking for something at the higher quality end of the spectrum. Its v small (6"W x 2 1/2"H x 7 1/2"D) runs on a battery which is charged by a wall-wart and really has no controls beyond on/off and mm/mc. Given the very low power demand, I would leave it plugged in and turned on all the time; and of course you would not need to adjust the mm/mc switch unless you changed carts.
Lower cost but still very good option would be Lehman Black Cube. Its about 4.5" x 4.25" x 1.75".
A final choice would be Benz-Lukaschek PP-1. which as I recall is about the size of a good-size universal remote; maybe about 3" x 8" x 1". I owned all three but used them with different carts. I liked the Artisan the best and the Benz the least, but both Benz and Black Cube now have newer versions on the market. And the Artisan is available at a heavily discounted price from Sorasound, which, unless there are special synergy issues, kind of makes the Benz superfluous.
Sutherland Ph-3D
The Sutherland Ph-3D is powered by 12 D sized batteries. Not only do you have to change out the batteries after a certain number of hours of listening, you have to turn it on and off via a front panel toggle switch.

I'd go with a Dynavector P75MkII.


Try the Musical Surroundings Phenomena. It costs $600 and has huge adjustability to suit nearly any cartridge. I have one paired to a Benz Micro ACE low output and it is magnificent. It also easily meets your size requirements and is solid-state, always-on. So, you plug it in and forget about it. It will be perfectly happy behind your pre-amp.
Nagra BPS, very small great sounding battery operated and affordable. They are coming out with a power supply soon for it.