Hitachi SR-903 Restoration
- Thread starter Fredrik 1977
- Start date
Fredrik 1977
Super Member
FINALLY!
well this was a first!
i ended up threading M5 and i barely got it to come off.
that knob aint in great shape. well i will not care about that now, ill go on restoring the rest and we´ll see how i end up doing with the knob. use a similar (i have one) or make a new one (w/o grip pattern) or try to fix this one best i can.
well this was a first!
i ended up threading M5 and i barely got it to come off.
that knob aint in great shape. well i will not care about that now, ill go on restoring the rest and we´ll see how i end up doing with the knob. use a similar (i have one) or make a new one (w/o grip pattern) or try to fix this one best i can.
Last edited:
Fredrik 1977
Super Member
Soo! pre-amp looks like this
i see one more relay,
8pcs C1344 that makes a total of 23
not counting the tuner
and good quality pots and switches.as i said before this unit looks pretty serious!
also 14pcs 10uf mkt and 4pcs 1uf mkt would be required for the preamp alone have to think about using nichicon UKL for those 10ufs.
i see one more relay,
8pcs C1344 that makes a total of 23
not counting the tunerand good quality pots and switches.as i said before this unit looks pretty serious!
also 14pcs 10uf mkt and 4pcs 1uf mkt would be required for the preamp alone have to think about using nichicon UKL for those 10ufs.
Last edited:
Fredrik 1977
Super Member
no that was from before. as the knob wobbled and has scraped the faceplate.
the knob had 2 big dents probably from a blow, maybe dropped?
the big mark on faceplate to the left of the shaft (or under the shaft on pic) is probably from the impact pushing the knob into the faceplate at that point. and then wobbling ever since..
well i bought it cheap, as is.
the rest of the knob i messed up
gotta fix the bent shaft also w/o breaking it.
better pic of the 2 dents, maybe the unit at one time was on fire and someone tried to put it out with a fire axe
to the right is the knob i have from unknown unit.
the knob had 2 big dents probably from a blow, maybe dropped?
the big mark on faceplate to the left of the shaft (or under the shaft on pic) is probably from the impact pushing the knob into the faceplate at that point. and then wobbling ever since..
well i bought it cheap, as is.
the rest of the knob i messed up
gotta fix the bent shaft also w/o breaking it.
better pic of the 2 dents, maybe the unit at one time was on fire and someone tried to put it out with a fire axe
to the right is the knob i have from unknown unit.
Last edited:
Fredrik 1977
Super Member
anyhow i placed an order with the stuff i dont already have. so i´ll start messing around in here soon.
ordered a new protection relay, anybody have experience with "Finder" brand? supposedly italian,
current relay is a Takamisawa MAT4B-BL 12VDC
ordered a new protection relay, anybody have experience with "Finder" brand? supposedly italian,
current relay is a Takamisawa MAT4B-BL 12VDC
Last edited:
Fredrik 1977
Super Member
K the first PCB is recapped!
its that little strange one refered to as "SUB BOARD" in the schematic.
the ordered parts havnt arrived yet but i have most of whats needed in stock so i might as well get started.
LOL one 3,3 nichicon UPW less in my assortment now,
its that little strange one refered to as "SUB BOARD" in the schematic.
the ordered parts havnt arrived yet but i have most of whats needed in stock so i might as well get started.
LOL one 3,3 nichicon UPW less in my assortment now,
Fredrik 1977
Super Member
Phono RIAA
recapped, but not the way i would want to. since this amp is full of 10uf caps in the signalpath it would be rather expensive to go with MKT.
i have to concentrate those mkt´s where it really matters.
input coupling is now 1uf Elna RFS (Silmic) output coupling is some regular 10uf nichicon VP Bipolar. so i thought it was no point in hyping out on the the other 2 , so i just used some Vishay BC General Purpose 47/50V
Upper part is the RIAA
Lower PCB is part of the tuner so i´ll leave that be.
not often you see Reed realys for muting low level audiosignal. its used in very high end cd-players.
cant really remember seeing that on a tuner inside a mid-class receiver before. or in any receiver for that matter.
recapped, but not the way i would want to. since this amp is full of 10uf caps in the signalpath it would be rather expensive to go with MKT.
i have to concentrate those mkt´s where it really matters.
input coupling is now 1uf Elna RFS (Silmic) output coupling is some regular 10uf nichicon VP Bipolar. so i thought it was no point in hyping out on the the other 2 , so i just used some Vishay BC General Purpose 47/50V
Upper part is the RIAA
Lower PCB is part of the tuner so i´ll leave that be.
not often you see Reed realys for muting low level audiosignal. its used in very high end cd-players.
cant really remember seeing that on a tuner inside a mid-class receiver before. or in any receiver for that matter.
Last edited:
Fredrik 1977
Super Member
well i changed my mind
i recaped the lower part of the pcb.
i only used General Purpose caps here, nothing fancy.
lower part of RIAA/Tuner Relays PCB
i recaped the lower part of the pcb.
i only used General Purpose caps here, nothing fancy.
lower part of RIAA/Tuner Relays PCB
I did wonder about C908 - wrapper looked a bit shrunk in the photo
Fredrik 1977
Super Member
and i didnt touch all those C1344´s in the relay circuits. since its not gonna do anything to the sound of the unit.
im in for a leg twisting marathon (will use BC546B) in the pre amp so i really dont want to make a head start with that LOL.
the knob: well i dont know whats the best way to go, that unknown knob is a liiitle bit bigger in diameter. but maybe it will look wrong. maybe try to fix the original knob in some way.? idunno.
im in for a leg twisting marathon (will use BC546B) in the pre amp so i really dont want to make a head start with that LOL.
the knob: well i dont know whats the best way to go, that unknown knob is a liiitle bit bigger in diameter. but maybe it will look wrong. maybe try to fix the original knob in some way.? idunno.
Last edited:
Fredrik 1977
Super Member
and yeah shure enough, the protection relay is crap! i started the unit to check some voltages and while at it i pulled the cover on the protection relay. and fiddled with the contacts. got sound right away!
it was totally greasy! dunno what the heck they "lubed" it with...looked like a mixture of butter and pubic hair lol
gave it a shot of break cleaner. followed by crc electronic cleaner. and worked it a bit by hand. and it seems to be working now,
new relay is in the mail so this one will be good target practice later with my air rifle
it was totally greasy! dunno what the heck they "lubed" it with...looked like a mixture of butter and pubic hair lol
gave it a shot of break cleaner. followed by crc electronic cleaner. and worked it a bit by hand. and it seems to be working now,
new relay is in the mail so this one will be good target practice later with my air rifle
Last edited:
The Fuxtor
Addicted Member
I have a botched amp board unit for spare parts if you need. The case is still in very nice shape but not so sure about the knobs...
Fredrik 1977
Super Member
thanks Fuxtor!
good to know...maybe need a tuning knob, maybe.
while waiting for the order
i googled some and found this http://stereonomono.blogspot.se/2014/04/hitachi-sr-903.html
"Hitachi Class G Stereo Receiver SR-903 (1977)
The SR-903 is a great match for power-hungry speaker systems. The low power output stage of the SR-903 delivers 75 watts per channel RMS. However, during musical peaks, the high output stage automatically produces 160 watts per channel RMS to prevent clipping and distortion."
" uses a low power and a high power output stage operating together.. At low signal levels the lower power stage drives the speakers. The transition to the more powerful output transistors .. Takes place smoothly at the point where it, becomes advantageous to do so."
The point they're talking about, of course, is where certain portions of the music you listen to demand more than the rated output to sound like they should. So when your music really gets thrilling, Class G cuts into a standby amplifier. Then, for just a moment, the SR-903 can pump out a lusty 160 watts per channel - without clipping.
As a wrap-up. Stereo review said Class G delivers "much higher overall efficiency than a conventional device, and this brings immediate dividends … in reduced weight, size and power consumption."
can anyone explain how that works? thats why there are 2 sets of outputs screwed to the heatsink?
2 amps in one....lol
good to know...maybe need a tuning knob, maybe.
while waiting for the order
i googled some and found this http://stereonomono.blogspot.se/2014/04/hitachi-sr-903.html
"Hitachi Class G Stereo Receiver SR-903 (1977)
The SR-903 is a great match for power-hungry speaker systems. The low power output stage of the SR-903 delivers 75 watts per channel RMS. However, during musical peaks, the high output stage automatically produces 160 watts per channel RMS to prevent clipping and distortion."
" uses a low power and a high power output stage operating together.. At low signal levels the lower power stage drives the speakers. The transition to the more powerful output transistors .. Takes place smoothly at the point where it, becomes advantageous to do so."
The point they're talking about, of course, is where certain portions of the music you listen to demand more than the rated output to sound like they should. So when your music really gets thrilling, Class G cuts into a standby amplifier. Then, for just a moment, the SR-903 can pump out a lusty 160 watts per channel - without clipping.
As a wrap-up. Stereo review said Class G delivers "much higher overall efficiency than a conventional device, and this brings immediate dividends … in reduced weight, size and power consumption."
can anyone explain how that works? thats why there are 2 sets of outputs screwed to the heatsink?
2 amps in one....lol
Last edited:
Goldie99
Super Member
I've been googling too..... http://www.updatemydynaco.com/HistoricDocuments/ClassG.pdf looks like the '76 description of the SR-903
Fredrik 1977
Super Member
wow so the class D is that old huh? didnt know that!
Fredrik 1977
Super Member
thanks goldie!
alright now im starting to understand the strange schematic!
i was wondering about why i had 2 sets of filter caps and 2 sets of DC rails. one +-70V and one +-33V
this is starting to get interesting!
this must have been pretty hightech back then? well atleast in the hifi dept
alright now im starting to understand the strange schematic!
i was wondering about why i had 2 sets of filter caps and 2 sets of DC rails. one +-70V and one +-33V
this is starting to get interesting!
this must have been pretty hightech back then? well atleast in the hifi dept
Last edited:
Goldie99
Super Member
Seems to have been up there yeah - and looks like it was probably the first commercial Hi-Fi receiver using it. Seems a little reminiscent of the NAD PE ('power-envelope') approach as well - so it might be worth checking for upgrades to the NAD PE series amps, there's probably some overlap.... and a lot more information about.
D. Self cites the Hitachi, and gives some background to why it maybe didn't really take off back then: http://www.douglas-self.com/ampins/classg/g.htm
D. Self cites the Hitachi, and gives some background to why it maybe didn't really take off back then: http://www.douglas-self.com/ampins/classg/g.htm
Fredrik 1977
Super Member
this is surprise #2 for shure!
cant wait to get finished and have good listen
the two 6800/80V will be replaced with 12000/80 Panasonic T-UP Snapins
the dual 5600/40V will be replaced with 2pcs of Vishay BC 10000/40V Snapins
cant wait to get finished and have good listen
the two 6800/80V will be replaced with 12000/80 Panasonic T-UP Snapins
the dual 5600/40V will be replaced with 2pcs of Vishay BC 10000/40V Snapins
Last edited:
ihmark
Active Member
On my SR-904, Hitachi calls it a class G receiver.
