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Scott R75s rebuild questions

Oh yeah, do you find that the Scott sounds really, really good when you turn it up, like crazy good? Mine gets very loud, fast, and I don't think I've ever turned it up past 11 o'clock (I am very cautious about design parameters--just because a volume knob goes all the way clockwise does not mean it should get anywhere near there, methinks).
 
I find FM to be very loud--like you said, never much past 11. I assume the preamp is pretty high gain. I use the tape inputs for iPhone and MacBook inputs. Those are obviously less sensitive. I have to jack the output levels of the source pretty high to max out the amp. I can turn the volume to 5 o'clock on those.
 
Scott75s1974 said:
I find FM to be very loud--like you said, never much past 11. I assume the preamp is pretty high gain. I use the tape inputs for iPhone and MacBook inputs. Those are obviously less sensitive. I have to jack the output levels of the source pretty high to max out the amp. I can turn the volume to 5 o'clock on those.
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Holy cow, 5 o'clock?! I max the volume on this MacBook Pro, add a Loudness curve with the Apple equalizer, and I get a nice, fat, juicy signal through either of the TAPE inputs. I had it up to 12 o'clock today while I was rowing--the highest I've ever had it--and it sounded as good as it's ever sounded. Absolutely incredible---what made me realize I had something special back when I first got it off Ebay. What you say about FM being strong due to high preamp gain makes sense--but I'm not complaining. I'll take a strong FM source any day.
 
I'm thinking of making up some t-shirts that say "Great Scott!" with a pic of an R-series receiver under that copy. The Scott may or may not have lightning bolts coming out of it.
 
birchoak said:
Holy cow, 5 o'clock?! I max the volume on this MacBook Pro, add a Loudness curve with the Apple equalizer, and I get a nice, fat, juicy signal through either of the TAPE inputs. I had it up to 12 o'clock today while I was rowing--the highest I've ever had it--and it sounded as good as it's ever sounded. Absolutely incredible---what made me realize I had something special back when I first got it off Ebay. What you say about FM being strong due to high preamp gain makes sense--but I'm not complaining. I'll take a strong FM source any day.
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Sorry, I try to keep the other device outputs at 50%. With very demanding music I think their small amps clip and distort. So let the Scott power boards do the heavy lifting.
 
Scott75s1974 said:
Sorry, I try to keep the other device outputs at 50%. With very demanding music I think their small amps clip and distort. So let the Scott power boards do the heavy lifting.
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Huh. I never thought about that. Makes sense. I'll try that next workout.
 
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Leestereo said:
C2: increase to 3.3µF (to lower F3 to 5Hz, i.e., 2 octaves below 20Hz).
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Thanks again for the advice on this cap on the driver board.

I'm wondering whether I don't have too much low bass for my speakers (Heath AS-2a = AR2a -- FR 42-20khz) -- losing energy to things they can't play, draining from the frequencies they can play. One demanding song in particular bogs down my receiver. I notice that the woofer is working hard at what I would guess is 10-15hz--I can see it, but can't hear that on these 10" acoustic suspension woofers. (I have a signal gen app that goes down to 20hz -- and that is visibly faster).

Is there a formula I can consult to raise the floor a bit? The original value was 2.2uf.
 
I just read through this thread because I was lucky enough to find a Scott R75S at the local flea today. The guy said it didn't work and was willing to part with it for $20 so I took a chance. I wasn't sure if I got a deal; it was filthy. I grabbed a bottle of 409 and took a few layers off and to my surprise it cleaned up very nicely. Next I took the top off to see if the filter caps looked OK and nothing was leaking. After vacuuming the interior, I decided to plug it in and have a go with the DBT. I brought it up slowly on the variac and to my shock and surprise it powered up without a hitch. While it was on I measured the DC offset (.05 and .07) respectively. Having gone this far I figured what the heck, added an FM antenna and plugged in my phones, tuned to one of the nearby stations and it sounded great! (well as good as any FM radio sounds) :). So now that I know it has good bones, I think this one will be a keeper. A lot to do in the way of cosmetics though. The plexiglass is loose and there are no lights at all that work. Also, the speaker switch seems to be stuck on the 1&2 position. Side panels need to be refinished. All the RCA jacks are very dirty - Can anyone give me a tip on the best way to clean these? Most importantly, kudos to @Scott75s1974 for documenting all the work on this model. One thing I don't understand, why isn't this receiver more highly thought of or sought after? It's built like a brick outhouse.
 
I owned its big brother, the R77S, traded it towards a MAC 1700, big mistake, traded it toward a Sansui AU-7700, keeper, so I had it restored by QRX Restore.
I loved my R77S with an FX Audio 01J tube buffer in between the preamp outs and the main ins.
You got a great buy!
 
infullview said:
I just read through this thread because I was lucky enough to find a Scott R75S at the local flea today. The guy said it didn't work and was willing to part with it for $20 so I took a chance. I wasn't sure if I got a deal; it was filthy. I grabbed a bottle of 409 and took a few layers off and to my surprise it cleaned up very nicely. Next I took the top off to see if the filter caps looked OK and nothing was leaking. After vacuuming the interior, I decided to plug it in and have a go with the DBT. I brought it up slowly on the variac and to my shock and surprise it powered up without a hitch. While it was on I measured the DC offset (.05 and .07) respectively. Having gone this far I figured what the heck, added an FM antenna and plugged in my phones, tuned to one of the nearby stations and it sounded great! (well as good as any FM radio sounds) :). So now that I know it has good bones, I think this one will be a keeper. A lot to do in the way of cosmetics though. The plexiglass is loose and there are no lights at all that work. Also, the speaker switch seems to be stuck on the 1&2 position. Side panels need to be refinished. All the RCA jacks are very dirty - Can anyone give me a tip on the best way to clean these? Most importantly, kudos to @Scott75s1974 for documenting all the work on this model. One thing I don't understand, why isn't this receiver more highly thought of or sought after? It's built like a brick outhouse.
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Sounds like a great purchase. That offset is great. The Plexiglas was attached with what seems to be hotmelt glue. It's a bit tricky, because the faceplate is such a thick extrusion that it cools on touch. I've redone mine once, and need to do it again.

There are some threads on here somewhere where people polish RCA jacks using a suitably sized hex socket lined with a piece of cloth and silver/brass cleaner--chucked into a drill and spun.

HH Scott's bankruptcy was reportedly from its refusal to compromise on quality in the face of cheaper imports. I've read they only made one top quality tuner and put it in everything (not sure if that was still true in these). The R7xS line looks like a massive refusal indeed. The internals are ridiculously overbuilt. It has a tube style chassis to hold the daughterboards with countersunk and planished threaded inserts. They really didn't need to do that. Epoxy glass circuit boards in 1974. High quality components.

It feels like a very serious piece of equipment, but that's not as obvious with the top on. It took me a while reading other rebuild threads to realize that much more sought after pieces just don't have near the build quality.

I haven't listened to many different systems. But I remain amazed by the lush sound my R75 produces with the Heath AS-2a (AR-2a kit) speakers. It was my grandfather's system.

Be careful cleaning that faceplate. That was my one unfixable error.
 
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Scott75s1974 said:
Thanks again for the advice on this cap on the driver board.

I'm wondering whether I don't have too much low bass for my speakers (Heath AS-2a = AR2a -- FR 42-20khz) -- losing energy to things they can't play, draining from the frequencies they can play. One demanding song in particular bogs down my receiver. I notice that the woofer is working hard at what I would guess is 10-15hz--I can see it, but can't hear that on these 10" acoustic suspension woofers. (I have a signal gen app that goes down to 20hz -- and that is visibly faster).

Is there a formula I can consult to raise the floor a bit? The original value was 2.2uf.
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I replaced them with the stock 2.2uf. I realized I was just trying to play a song that my system can't handle. Lost a bit of low end on more manageable pieces. I'm going to go back the the 3.3uf you recommended.
 
Scott75s1974 said:
Be careful cleaning that faceplate. That was my one unfixable error.
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Oh ya! I noticed right away that the brushed aluminum look is some kind of coating. Used nothing but mild soap and water, and a little mineral spirits to clean where someone had put scotch tape on the top of the face plate. After I cleaned the front panel, I used a very light coating of semi gloss clear lacquer to prevent further degradation. This does not change the look and is very close to invisible. I was able to free up all the switches with CRC spray cleaner. Tomorrow I'm going to get some CRC electrical spray lubricant from Home Depot to use on the switches and also to use after after I Deox the pots. Ordered 10 GE1866 lamps from Amazon to replace the dead bulbs. I think this will be around an 8 out of 10 when I get done with all the cosmetic stuff.
 
I damaged it by soaking in very warm water and Dawn dishsoap. But I've found that denatured alcohol is fine. I tried to use some lacquer thinner to reconsolidate some parts of the finish, that did nothing either. So it pretty much is impervious to anything except warm water and dish soap. Go figure.
 
Forgot to update that I doubled the filter caps as well. I just couldn't sit with those extra spaces unused. (Stock is 2x 5000uf on these. The R77s comes with 4x 5000uf so it's designed to handle these). So now there are 4 x 6800uf. I used Nichicon Gold Tune, but have since learned there are many cheaper excellent caps for power supply use. I also did the Triac power switch mod in case this provided too much of a startup load for the switch. (But given the R77s design, I don't think it does.)

Might help with heavy transient demand. I wanted to do everything I could to improve this b/c of its sentimental value.

IMG_2046.JPGIMG_2048.JPG
 
Scott75s1974 said:
I damaged it by soaking in very warm water and Dawn dishsoap. But I've found that denatured alcohol is fine. I tried to use some lacquer thinner to reconsolidate some parts of the finish, that did nothing either. So it pretty much is impervious to anything except warm water and dish soap. Go figure.
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I guess I dodged a bullet then because I didn't let it soak. Just washed it like a dish and patted it dry. Nothing came off but you could see very small areas where the finish had be scraped near the edge and the aluminum was shiny where the coating had come off. Did you loose any of the lettering?
 
infullview said:
I guess I dodged a bullet then because I didn't let it soak. Just washed it like a dish and patted it dry. Nothing came off but you could see very small areas where the finish had be scraped near the edge and the aluminum was shiny where the coating had come off. Did you loose any of the lettering?
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I think my finish has been damaged by UV over the years. It's slightly golden toned. Thankfully the finish around the printing is secure. That might have blocked the UV and kept the underlying finish secure.
 
Scott75s1974 said:
Forgot to update that I doubled the filter caps as well. I just couldn't sit with those extra spaces unused. (Stock is 2x 5000uf on these. The R77s comes with 4x 5000uf so its designed to handle these). So now there are 4 x 6800uf. I used Nichicon Gold Tune, but have since learned there are many cheaper excellent caps for power supply use. I also did the Triac power switch mod in case this provided too much of a startup load for the switch. (But given the R77s design, I don't think it does.)

Might help with heavy transient demand. I wanted to do everything I could to improve this b/c of its sentimental value.

View attachment 2050384View attachment 2050385
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Just wondering why you replaced what look like green Mylar caps with what look like Wima?
 
I didn't do them all. Some of the green mylars had gaps in the coating. So I figured I'd replace them and their circuit siblings. I probably replaced more than necessary. They were probably fine. I think maybe I did just the ones on the driver boards.
 
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