Seems that the power wires may be too small. That will lower the power output of the amp. If it is going to require as much as 30 amps to drive in full output; then some decent gauge wire will be required to feed it.
Are you driving it with the right amount of RF power to the amp input?
Too much RF power input has been known to cause these amps to fail; be careful not to over-drive the input.
See the specs below:
From H&Y Electronics:
* MODES: AM/FM/SSB/CW
*FREQUENCY RANGE: 20-30mhz
*POWER SUPPLY/voltage: 12-14Vcc
*IN/OUT ENERGY/amperage: 12-30A
*RF INPUT POWER: 1-6W AM/FM - 1-12W SSB/CW
*OUTPUT POWER: 60-250W AM/FM - 120-450W SSB/CW
*SWR:1.1-1.5
* FUSES: 3x10AMP
Since this amp will draw no more than 30 amps under full load, I would have to say that I wouldn't expect more than 250 watts on AM mode and no more than 320 watts on SSB mode when driven with the proper RF input power.
I don't know what kind of devices they use in this amp - 2290's, 1446's, 2879's (doubtful), or MOSFET's (most likely for that price); but I wouldn't over-drive it.