These are great receivers after you re-cap them and replace all the transistors. This is last great year for Hitachi receivers. The 903 was very highly rated by the testing lab magazines when it came out.
Ok, so this is probably one of the more powerful receivers from the late 1970's early 1980's. Rated at 75wpc and 150wpc (short duration class G). The first mistake people make is to refer to the SR-903 as a 150wpc unit. It has two pairs of output transistors, low for 0-75w and high for 75-150w. The high transistors only operate briefly for loud passages of music. The confusion dates back to the early 1970's when manufactures used terms such as MUSIC POWER and IHF POWER. They made some crazy claims to output power for their products. In 1978 the IHF (Institute of High Fidelity) ruled that amplifiers would be rated for headroom (reserve non clipped power) in decibels. A 50wpc receiver with 1.5 decibels would put out 75wpc. With 3 decibels you'd get 100wpc. Hitachi's class G receivers have 3 decibels of headroom, giving a clean crisp sound. I've probably over simplified this but I hope you folks get it.
Except the specs for this SR-903 Class G state 75wpc (@ 8 Ohms, 20Hz-20KHz, 0.1% T.H.D.) up to 160wpc for the peak/transients (i.e. IHF power). [95wpc @ 8 Ohms, 1Khz, 0.1% T.H.D.; 105wpc @ 4 Ohms, 1Khz, 0.1% T.H.D.]
@@jb678901- yeah, that IHF (Institute of High Fidelity) power designation went into effect in late 1978. According to IHF standards all amp headroom would be specified in decibels (not music power or reserve power). Hence the SR-903 had 3dB's of headroom equivalent to twice it's rated output power of 75wpc (for short term). And the receiver top is still barely warm after hours of use. My SR-804 purchased in 1979 is class G with 50wpc and 3dB's headroom of 100wpc. It's still my main amp after forty four years. Also note that any amplifier that puts out more power into 4 ohms than into 8 ohms is well designed. When the SR-903 was sold (1977/1978) the IHF had not yet made this new ruling.
@@martyjewell5683 Technically, it's just over 3dB of headroom on the SR903...which probably explains why the Hitachi service manual (July 1977) states "Music Power (IHF): 160W/ch + 160W/ch (8 Ohms)" on page 2. On that same page it states "Output RMS Power (Both channels driven): 75W/ch + 75W/ch (8 Ohms, 20Hs-20kHz, T.H.D. 0.1%)" Interestingly, the Service manual covers the SR-903, SR-803, and SR-703. The SR-803 on that same page (different column) states "Music Power (IHF): 80W/ch + 80W/ch (8 Ohms)" and "Output RMS Power (Both channels driven): 50W/ch + 50W/ch (8 Ohms, 20Hs-20kHz, T.H.D. 0.1%)"
had one years ago but it started cutting out on one channel, had it repaired less than six months later the same trouble returned. Very high power consumption around 380 watts
@@mr.blackhawk142 I bought one ($134)...very minty condition. Had it professionally checked (replaced a few transistors and caps, but not a full recap). It's a very clean and more clinical sounding unit...not too warm. Just wonderful. Liked it so much, I grabbed a second unit ($115) 6 months later in a local auction. These units are really built well. Nice wiring, fully marked PCB's, Hitachi parts. ALUMINUM face, knobs, buttons, levers. I was so impressed with these SR-903's that when an SR-503L came up for $120...I went for it too. This one was fully revised (caps, issue transistors, lights, etc.) by the seller (he used it as a temporary amp while his primary unit was in for a planned revision). Absolutely perfect specimen. Nice 20wpc (8 Ohm/RMS) for the office desktop. I have found these Hitachi's to fly under the radar a bit...no Marantz, Pioneer, Sansui (...Yamaha, Luxman) tax with these units...at least not when I was buying them...the auction traffic was very limited.
