Sansui SEVEN Questions and Possible Restoration

[DAY4201]

I found and bought for a good price a Sansui Seven several years ago. It is in very good cosmetic condition and pretty clean inside although it appears that it may have been stored for some time in a somewhat damp basement or garage as there is some slight corrosion seen in places.

As I have completed a few receiver restorations I am now focusing on the Seven. I am trying to be more methodical then in the past with both approaching and recording condition before restoring and whatever I do in terms of a “restoration”.

I have learned for the best here on AK that problems should be fixed before any attempt at a restoration. With that in mind here is what I have done so far.

Visual inspection reveals no leaking caps, burns or fired components, powers on DBT.

Now off DBT, I have been able to set the Output Balance Alignment (DC offset I assume) to 8-10 mVDC for both channels. Also set Current Alignment of Power Amp (bias adjustment again I assume) to 13+mA (some fluctuation) according to pg. 24 of the service manual for both channels. Old trim pots seem OK but will replace with new multi-turn at some point.

I have cleaned all the pot’s and a few of the push switches I could get to. Listened to speakers using tuner, tape and AUX. Have yet to connect phono but will soon. All sound good but I assume could sound better. Tuner seems quite sensitive especially FM without an antenna in my basement workshop.

All lamps and mode lights work. Tuning and signal meters appear to function properly.

One question I have for those familiar with the Seven. I see that the power indicator which works, and the mode indicator lights up, but the panel only lights up when the tuner is selected. Otherwise, it is dark. Is that the way it works or is there something not working right?

I’m sure I will have more questions as I go along with this restoration. Also, I have not seen much in the way of info on restoring this model. I have the schematic and take lots of photos but am wondering if I am missing any detail on previous restorations.

As always thanks to all to can help here and in the future with this project.

 

[sanjib]

"One question I have for those familiar with the Seven. I see that the power indicator which works, and the mode indicator lights up, but the panel only lights up when the tuner is selected. Otherwise, it is dark. Is that the way it works or is there something not working right?"

Absolutely normal for this Sansui model and also for some other models of that era!

 

[DAY4201]

"One question I have for those familiar with the Seven. I see that the power indicator which works, and the mode indicator lights up, but the panel only lights up when the tuner is selected. Otherwise, it is dark. Is that the way it works or is there something not working right?"

Absolutely normal for this Sansui model and also for some other models of that era!

Thanks for your quick response. I have to say I am a bit disappointed as it seems rather odd and not very pleasing to the eye. But I am really glad that there is no problem with the lighting. I'll probably replace those old lamps but not something to mess with right now. Thanks again!

 

[sanjib]

You can make some changes in the connection to make dial lights always on. Search here and I believe you will find a thread on this topic

 

[DAY4201]

You can make some changes in the connection to make dial lights always on. Search here and I believe you will find a thread on this topic

Thanks I did find a few threads that look like they will help.

 

[DAY4201]

Still familiarizing myself with this unit. Taking photos, checking for schematic and parts list. Question: It appears Sansui liked to use a lot of fusible resistors which should be replaced with comparable metal film. the parts list doesn't specifically identify them.

Can I assume that any 1/2W (usually 10%) and any identified as 1/4W 5% are fusible and should be replace with same wattage and maybe a lower percentage if available? Thanks!

 

[gslikker]

I had a link to my previous resto some years ago but my info has moved, you can see some pics here. Particularly hard to remove and put back are the power board sticking out through the metal having all these wires and the tone board having all those short wires.

http://www.gerardslikker.nl/sansui-seven.htm

In the meantime, my Sansui still works but something is wrong with the relay switching on too fast and the pushbutton switches wearout makes one needs to push them a few times, especially if the unit is out of use for a long time. I do not bother to open it once more, the mechanical wear-out of the switches probably can not be undone anyway without replacement. BTW I never had those pushswitches out of the unit and those were not refurbished which I should have done (among probably other things, too, reading back my web page) Also those are probably not easy to take out.

The Seven is definately NOT built to be serviced.

 

[DAY4201]

I had a link to my previous resto some years ago but my info has moved, you can see some pics here. Particularly hard to remove and put back are the power board sticking out through the metal having all these wires and the tone board having all those short wires.

http://www.gerardslikker.nl/sansui-seven.htm

In the meantime, my Sansui still works but something is wrong with the relay switching on too fast and the pushbutton switches wearout makes one needs to push them a few times, especially if the unit is out of use for a long time. I do not bother to open it once more, the mechanical wear-out of the switches probably can not be undone anyway without replacement. BTW I never had those pushswitches out of the unit and those were not refurbished which I should have done (among probably other things, too, reading back my web page) Also those are probably not easy to take out.

The Seven is definately NOT built to be serviced.

Thanks for your reply to my post and especially for the link to your website. As I have found almost no info on restoring the SEVEN your website will be helpful! I would certainly agree that the SEVEN is not built to be serviced. Maybe that is why I have put it off until I did other more easy restorations. So far I have found 2226 Marantz I recently mostly completed (still testing it) to be probably the easiest other than a Kenwood KA-7100 integrated amp. Easy access to the boards on both.

While I still intent to replace the main filter caps first. I have been looking at the Driver Block bd (F-1439). Just trying to get a sense of the replacements for the transistors except for the bias regulating transistors.

Looking at substitutes for the TR808 (2CS1124, NPN) (subs include KSC3503DSTU and KSC2690AY) and TR809 (2SA706, PNP) (subs include KSA1381ESTU & KSA1220AYS) it appears that they are all in a TO-126 package with ECB pin configuration. I have all the subs on hand.

TR808 and 809 pin configuration is EBC which means the base and collector pins will have to "crossed". I see that you replaced those transistors and attached them to the existing heat sinks. Is that necessary?

I have attached a photo of TR809 for reference and in case anyone else is interested.

 

[KeithD]

Can I assume that any 1/2W (usually 10%) and any identified as 1/4W 5% are fusible and should be replace with same wattage and maybe a lower percentage if available? Thanks!

I don't believe there are any fusible resistors in the Seven. Sansui used those in later models such as the x0x0 series and QRX-x001 series. Those were produced in the mid-70s and later. The Seven is from the early 70s. Fusible resistors are typically a different color such as gray, light blue, or light green. They were also mounted about 0.5 cm off the board incase they acted like a "fuse" and burned up.

I haven't restored/recapped my Seven yet. It's working perfectly at the moment and there are too many other projects ahead of it. I think the reason you don't see many restore threads on the Seven is that it is far overshadowed by the Eight and Eight Deluxe. Also, I find it less common (in the USA, at least) than the Eight/8D or the Six. I don't know why that is, but there are just fewer of them. In my experience the Seven is an excellent receiver and compares favorably in sound with the Eight; however, build quality in the Eight is much better and the best of what Sansui did.

Best wishes on your restore!

 

[gslikker]

T........... I see that you replaced those transistors and attached them to the existing heat sinks. Is that necessary?

I have attached a photo of TR809 for reference and in case anyone else is interested.

View attachment 2439613

TO126 transistor leads are long enough to make the lead twist using pliers. Dedicated TO-126 heatsinks are nice but the original ones are mechanically adapted to the circuit card, so no reason to not use them.

.....I don't believe there are any fusible resistors in the Seven. ....

Best wishes on your restore!

Indeed, they all look like carbon film ones.

 

[DAY4201]

I don't believe there are any fusible resistors in the Seven. Sansui used those in later models such as the x0x0 series and QRX-x001 series. Those were produced in the mid-70s and later. The Seven is from the early 70s. Fusible resistors are typically a different color such as gray, light blue, or light green. They were also mounted about 0.5 cm off the board incase they acted like a "fuse" and burned up.

I haven't restored/recapped my Seven yet. It's working perfectly at the moment and there are too many other projects ahead of it. I think the reason you don't see many restore threads on the Seven is that it is far overshadowed by the Eight and Eight Deluxe. Also, I find it less common (in the USA, at least) than the Eight/8D or the Six. I don't know why that is, but there are just fewer of them. In my experience the Seven is an excellent receiver and compares favorably in sound with the Eight; however, build quality in the Eight is much better and the best of what Sansui did.

Best wishes on your restore!

Thanks for your perspective on the Seven and the info on fusible resistors. I have encountered fusible resistors (one blown) several times in cassette decks (either JVC or Technics, its been a while) but I don't think I recall seeing them otherwise. Now I have a better idea what to look for if I encounter any (but as you say there may not be any on the 7). Thanks!

 

[DAY4201]

TO126 transistor leads are long enough to make the lead twist using pliers. Dedicated TO-126 heatsinks are nice but the original ones are mechanically adapted to the circuit card, so no reason to not use them.


Indeed, they all look like carbon film ones.

Thanks for taking your time to provide your expertise/ help to an average hobbyist.

I have decided to proceed with restoring the driver boards as I have all the replacement parts on hand for them except the trimmer resistors. They seem to be in working condition but I still will replace them. It appears you replaced VR801 (5K trimmer on mine) with a 10K trimmer. Is that an "upgrade" or does it make a difference? Part of the reason I ask is a have a 10K trimmer .5W on hand that would fit there.

I am always curious when others "upgrade" or otherwise change various components from the original. I am not often knowledgeable enough to know why. I can understand increasing capacitance and voltage on some capacitors which I have done mostly on advise from others. I have learned that a modest increase in capacitor voltages can be done in most cases without a problem and often to get a proper fit.

I have also seen that sometimes increases in capacitance may necessitate changes in other components which makes me a bit nervous as there is usually no explanation given. So, I mostly stick to the original value unless I understand why changes are made. However, I would like to learn more so I have to ask questions and try not to be a nuisance.

 

[gslikker]

the most important there is I apparently put a 1.8k resistor to the taper of the trimmer.
This way it just gives some more precise regulation of the zero output since the potentiometer actuation is less sensitive, this way.
I also put a capacitor of 1 uF over the 1.8k resistor, just to get rid of any possible noise of the potentiometer taper (probably overkill or maybe it does not help for anything).
I do not really know if this really matters but the goal was a more easy nulling and maybe I only had a 10k trimming potentiometer at hand at the time.
It is some time ago so I forgot....
Sometimes I just fiddle with extra resistors to adapt the potentiometers I have at hand.
In the end, trimming potentiometers is always a problem, they tend to have the legs on the wrong side, the legs too wide or too narrow, or the trimming screw appears no accessible when the thing is mounted, etc.

 

[stereofun]

Other items to consider are replacing electrolytics with film. For instance a critical coupling cap is the C801 1.5 uF. That couples signal from pre-amp to Power-amp (driver) On many integrated from that era you will find a film cap there. On the Eight I had an electrolytic, but you may find a tantalum, either way replace with a Wima polypropylene FKP series same uF or 2.2 if that's available.

C001/002 4700 could be uprated to 5600 or 6800 for a bit more peak reserve.

There are more esoteric things to tweak like differential balance and feedback loop, but not before you have a well sounding restored amp as a baseline.

 

[DAY4201]

Other items to consider are replacing electrolytics with film. For instance a critical coupling cap is the C801 1.5 uF. That couples signal from pre-amp to Power-amp (driver) On many integrated from that era you will find a film cap there. On the Eight I had an electrolytic, but you may find a tantalum, either way replace with a Wima polypropylene FKP series same uF or 2.2 if that's available.

C001/002 4700 could be uprated to 5600 or 6800 for a bit more peak reserve.

There are more esoteric things to tweak like differential balance and feedback loop, but not before you have a well sounding restored amp as a baseline.

Hi Tom, thanks for your input. C801 on my unit is a .68uF/25V white Elna tantalum not 1.5uF as shown in the schematic. You suggest replacing it with a polypropylene cap possibly a WIMA FKP or I assume an alternative is a WIMA MKP.

I have not found anything close (in polypropylene) .68uF to 2.2 uF that would possibly fit. Their lead spacing is too long plus their overall size is too large. Maybe I am not looking in the right place on Mouser and Digikey.

I assume reasonable alternatives, which I have on hand, are WIMA .68uF, 1uF, 1.5uF and 2.2uF all MK2 series, 5% @63V. Also, I do have some 1uF polyester Kemets, 5% @63V if that is a better choice?

I do intent to upgrade C001/2 from 4700uF to 6800uf. I have those. Nichicon LKS series which fit the existing holder.

I also plan to replace C003/4 from 1000uF to 1500uF using LKS series caps which I also have.

Thanks again for taking your time to offer suggestions. They are always appreciated.

 

[DAY4201]

the most important there is I apparently put a 1.8k resistor to the taper of the trimmer.
This way it just gives some more precise regulation of the zero output since the potentiometer actuation is less sensitive, this way.
I also put a capacitor of 1 uF over the 1.8k resistor, just to get rid of any possible noise of the potentiometer taper (probably overkill or maybe it does not help for anything).
I do not really know if this really matters but the goal was a more easy nulling and maybe I only had a 10k trimming potentiometer at hand at the time.
It is some time ago so I forgot....
Sometimes I just fiddle with extra resistors to adapt the potentiometers I have at hand.
In the end, trimming potentiometers is always a problem, they tend to have the legs on the wrong side, the legs too wide or too narrow, or the trimming screw appears no accessible when the thing is mounted, etc.

I now see you that you added your “mod” to the trimmer on the schematic on your website.

I think I have been able to find both 1k and 5k Bourn trimmers on Mouser that I believe will fit, # 652-3296P-1-102LF (3/8”, 1/2W). My concern is whether the wattage is OK? The parts list doesn’t specify that.

So far on the driver bd (F-1439) I have replaced:

C801 .68uF/25 Elna, white=> .68uF/63 WIMA MKS2. I can change that to a higher value if that is desirable.

C806 100uF/10 Elna, grey BP => 100uF/25, Nichicon UVP (BP). I have Nichicon UES same value but a bit larger if that is the better choice.

C809 47uF/50 Elna grey => 47uF/63 Nichicon UPM (low impedance). Could use a UKL if it is a better choice.

TR803/4 2SA678, green, => KSA1015YTA

I have pulled TR805 2SC983. It tested good. It’s hFE=78 which is within spec of either the O or R version according to the data sheet. It appears from searching AK that the earlier preferred replacement was KSC2383YTA, hFE= 160-320. Also the KSC1845 is listed as an alternative but it’s hFE @ 300-600 is much higher. I have both KSC2383YTA & KSC1845FTACT.

Does hFE matter here? Is higher better than lower if it does matter? I should note that I am aware that the KSC1845FTACT is the complement to the KSA992 which I plan to use as a replacement for TR801, 2SA640. But, I am still interested in the question regarding hFE in this case.

Thanks again for your help!

 

[stereofun]

MKP2 1uf - lead space 5 mm, looks like they are backordered from mouser at least. If the original is 0.68uf then this will do, I just wouldn't put in a smaller rating. Back then the design emphasis was not for the deep low end as that was more of a nuisance created by turntable rumble or wow & flutter from tapes. In the mighty 999 the engineers even installed a sub sonic-filter that pretty aggressively chokes bass from 100 hz down. Running a slightly larger than spec coupling cap is just an insurance policy that no low end is left behind with todays high res digital sources.

By the way, switching dielectic to polyester (mylar) you can keep lead spacings of 5mm all the way up to 6.8uF via the MKS2 series. Polyester is still better than electrolytic or tantalums, but polypropylene is just the better choice if you can fit the size you need.

https://www.mouser.com/ProductDetail/WIMA/MKP2C041001N00MN00?qs=RB4whv9F6rzjnMhXY4f0hA==

 

[merlynski]

 

[DAY4201]

MKP2 1uf - lead space 5 mm, looks like they are backordered from mouser at least. If the original is 0.68uf then this will do, I just wouldn't put in a smaller rating. Back then the design emphasis was not for the deep low end as that was more of a nuisance created by turntable rumble or wow & flutter from tapes. In the mighty 999 the engineers even installed a sub sonic-filter that pretty aggressively chokes bass from 100 hz down. Running a slightly larger than spec coupling cap is just an insurance policy that no low end is left behind with todays high res digital sources.

By the way, switching dielectic to polyester (mylar) you can keep lead spacings of 5mm all the way up to 6.8uF via the MKS2 series. Polyester is still better than electrolytic or tantalums, but polypropylene is just the better choice if you can fit the size you need.

https://www.mouser.com/ProductDetail/WIMA/MKP2C041001N00MN00?qs=RB4whv9F6rzjnMhXY4f0hA==

Thanks for the part reference. I found your explanation interesting. I like to use the best parts I can so I am a bit disappointed that it is not available.

 

[stereofun]

Thanks for the part reference. I found your explanation interesting. I like to use the best parts I can so I am a bit disappointed that it is not available.

Don't sweat it - just pop in a 1.5 MKS2 - still better than any electrolytic or 50 year old tantalum. You can always later pop in the polypropylene when available, I doubt you will notice any difference. Audible differences are imo more so accumulative when many small improvements are made throughout a restoration, then by the end they add up and you go..... hmm, better.