The 1804 plain 4 eagle struck in silver. Recent research by John Dannreuther has determined that these J34-J34A/P46-P47 are true die trials made in 1834 from old dies and were struck prior to the gold issues. The obverse die was an unfinished die with "180" already punched into the die, the "4" being added from a modern punch. The die was lapped to remove rust. The reverse die appears to be an unused 1806 half dollar die. For more information, collectors should read the August 14, 2006 and November 24, 2014 editions of Coin World.
In silver, about 4 or 5 are known with reeded edge J34/P46 with the Judd-Bass Foundation coin being the finest.
There is also a single example known struck with a plain edge J34A/P47 which is mentioned as being in the Ed Schuman collection. It would be interesting to see if this was the first one struck.
These 1804 eagles were struck in gold in 1834 for inclusion in the presentation proof sets presented to the leaders of southeast asia. The famous King of Siam proof set is still in existence today. Pollock delisted these in gold. Judd apparently listed them as J33 because of the silver trials listed below.
Photo courtesy of Stacks.