Marantz 510M full story:
https://picasaweb.google.com/110340960129324761372/MARANTZ510M02?authkey=Gv1sRgCLzL5cWG48aOaQ

General
Rarity X-Rare
Retail Price 999.95, June 20th 1975 Marantz Dealer List
Ebay High-bid $1913.00 (auction #1368022067, July 27/2002)
First Year 1975
Last Year 1978
Matching Preamplifiers 3600,3800
Wood Case WC-7 (WC-1 according to June 1975 list)
Blue Face Yes
Channels Two
Speaker Connections One set
AC Switch Yes
Physical
Width 15 1/2
Height 6 1/4
Depth 14
Weight 46
Amplifier
RMS Power Per Channel
256x2 (8Ohm)
350x2 (4Ohm)
Total Harmonic Distortion (THD) 0.05%
Power Bandwidth 20 Hz - 20 kHz
Intermodulation Distortion (IM) 0.03%
Gain Control(s) Dual
Meter Range Single: Off, 0 db (2.56 watts), +10 db (25.6 watts), +20db (128 watts, +3dB is 256 watts)
Peak Lamp(s) Yes
Output Meter(s) Dual
Cooling Fan(s) 2-speed