[Amps] Metron/TWE 500 watt SS amp - need help!

[North Pole]

I have a Trans World Electronics 500M with 8 Motorola MRF 454 transistor finals.  I was playing around the other night with my K2 qrp rig keying about 8 or 9 watts into the amplifier.  It amazed me how well it was working as I was getting an easy 100 plus watts and it seemed like I was still enjoying the qsk of the K2.

Unfortunately, I put my hand on the heat sink and it was hot.  Usually on ssb it hardly gets warm even with the occasional rag chew.  I looked at the amp meter and the collector was drawing 20 amps with no rf input.  I quickly shut things down.  The next morning I popped the cover just to give a visual inspection.  There is no apparent physical damage nor burnt odor.  

I put 50 or 60 watts of ssb rf into it last night and the amp easily put out over 500 watts drawing 70 amps on peaks.  But,again, once the mike was keyed it drew 20 amps without any modulation.

I am really not much of an electronics tech but open to any advice, comments or trouble shooting tips anyone may care to share.   Or if there is a repair service that will work on a Metron.  I hate to toss it out as I seldom need the 500 watts but its the only way I will get on 75 meters in the evening.

Meanwhile back to cw qrp with the good old K2.

Thanks for reading, Larry W8CCY