Sony TA-8650 filter cap replacement?

MattiaM

Active Member
I got my hands on a beautiful TA-8650 that I bought broken a couple of weeks ago and brought back to life.
It's the best example I have ever come across, nobody had ever worked on it, and it was in storage for a very long time (in a very dusty place). It came with 3 of 2SK60 gone and a burnt resistor, but I had 3 spare ones laying round with the same ranking, so after cleaning it (a LOT of dust) and recappping it entirely, it was up and again ready to be tested. All the biases checked correctly, the DC offeset too, I plugged the oscillocope and the signal generator and... nothing. No waveforms at all.
After a bit of troubleshooting, it turned out it was the switches, that were still in need of more cleaning (at firist I thought one of the ICs had gone bad). After taking them all apart (what a pain), now the amplifier is back and works quite nicely.
Two things though do not seem quite right:
the first is that it runs HOT. I am used to the fact that vfet amplifiers run hot, I have already a TA-4650, two 5650, and also a TA-F7 in my collection, but this one is on another level hot: I can't really keep my hand on the top cover at all, because it just burns, although the thermistors never sent the amplifier into overheat protection for now, even after a few hours of continuous operation. Is it normal that it is that much hotter of a 5650?
The second problem is a slighlty annoying hiss from the speakers, regardless of the volume, which can be heard quite distinctly at equal levels in both channels. I assume it is a power supply issue, although I have not investigated much for now.
In case I decided to replace the main filtering caps, those in the TA-8650 are quite unique. It has two double filtering caps, one large one with two 10000uF caps inside, and a smaller one with two 3000uF caps.
As the amplifier looks pristine, I want to keep the cans of the original caps to keep the original look. Especailly for tube gear, I have seen people emptying the cans and using them to put modern replacement caps inside, but I have never done it myself. Has anyone got any suggestions on how to do that?
IMG-0509.jpg
 
I have restored a couple Marantz power amps that used a dual cap can. Most just replace it with two caps as did I. I see two dual caps in your picture. It might be a tight fit. That hiss could be noisy signal transistors. My Sony 3200F had a hiss and turned out to be dirty gain controls. I have had amps that run so hot I couldn't keep my hand on the top. One lasted over 15 years. If the dual caps test good I would just leave them unless they are bulging, leaking or vented.
 
I got my hands on a beautiful TA-8650 that I bought broken a couple of weeks ago and brought back to life.
It's the best example I have ever come across, nobody had ever worked on it, and it was in storage for a very long time (in a very dusty place). It came with 3 of 2SK60 gone and a burnt resistor, but I had 3 spare ones laying round with the same ranking, so after cleaning it (a LOT of dust) and recappping it entirely, it was up and again ready to be tested. All the biases checked correctly, the DC offeset too, I plugged the oscillocope and the signal generator and... nothing. No waveforms at all.
After a bit of troubleshooting, it turned out it was the switches, that were still in need of more cleaning (at firist I thought one of the ICs had gone bad). After taking them all apart (what a pain), now the amplifier is back and works quite nicely.
Two things though do not seem quite right:
the first is that it runs HOT. I am used to the fact that vfet amplifiers run hot, I have already a TA-4650, two 5650, and also a TA-F7 in my collection, but this one is on another level hot: I can't really keep my hand on the top cover at all, because it just burns, although the thermistors never sent the amplifier into overheat protection for now, even after a few hours of continuous operation. Is it normal that it is that much hotter of a 5650?
The second problem is a slighlty annoying hiss from the speakers, regardless of the volume, which can be heard quite distinctly at equal levels in both channels. I assume it is a power supply issue, although I have not investigated much for now.
In case I decided to replace the main filtering caps, those in the TA-8650 are quite unique. It has two double filtering caps, one large one with two 10000uF caps inside, and a smaller one with two 3000uF caps.
As the amplifier looks pristine, I want to keep the cans of the original caps to keep the original look. Especailly for tube gear, I have seen people emptying the cans and using them to put modern replacement caps inside, but I have never done it myself. Has anyone got any suggestions on how to do that?
View attachment 1233814

1) I do not have a TA-8650 but I can tell you that it should not run that hot. Do you have acess to a curve tracer or to someone with a curve tracer that can look at those replaced transistors...if they were not of the same rank, the amp it would ran very hot as some of the transistors would be "working harder" than others. There are lots of fakes floating around...
2) what did you adjust the bias at? that could also cause the amp to ran hot.
3) the noise could come from the PSU, but could also come from the notorious op-amps that Sony use on these units. I have a TAE-8450 with a similar simptom on the phono stage. Have not yet looked into the root cause.

4) now the caps:
there are a few AKers that have replaced the main caps on these units with the EW suggested mode.
there are alternative methods that would look more OEM, but they are a bit more involved. Not sure how far you want to take this rebuild.
 
I finally had the time to do a bit more testing and the noise is definitely coming from the preamp section: with the preamp disconnected and the amp inputs shorted, the amp is dead quiet.

Do you have acess to a curve tracer or to someone with a curve tracer that can look at those replaced transistors
I managed to get quite a good stock of vfets about a year ago, and I decided to buy a Tek 576 that I found really cheap to test them, so I can say for sure that the 3 new 2SK60 that I installed are in fact the actual 56 rank that they show.
I can't test the original vfets that the amplifier came with, as I sold the tek (I just don't have enough space unfortunately, and I am still regretting that decision). However, they look all original, and they appear to be one of the first vfet batches ever produced by Sony. Given that the amplifier appears to have never been opened (all the screws had not a single scratch), I am inclined to think that they're the original ones installed by Sony. As a comparison, you can see in the picture attached the early ones (K56) and more modern ones, the early ones have a less shiny case compared to later production (the later ones are surely what they say they are on the case, as they checked with the curve tracer).

Dirty selector switches will give you lots of cross-talk between the sources which also makes them strong candidates for a good scrub
I believe this is actually the case, given how much dust there was inside. Cleaning the switches on teh switch board with deoxit didn't do any good, and I had to actually open all the switches and clean the pins with contact cleaner and fine sandpaper, to make them work again properly. However, I did not open the monitor and function switches, as well as the tape copy and ext. adapter because I don't know how to open them, they look riveted on all sides, so it seems that the only way to get inside is to remove them and (maybe?) open them from the bottom. Maybe you have suggestions on how to access the inside of them?

there are alternative methods that would look more OEM, but they are a bit more involved. Not sure how far you want to take this rebuild.
I'd love to keep the originality, as this amplifier is really pristine and I think worth the effort; I'd love to hear about these alternative methods. :)

IMG_0364_small.jpg IMG_0365_small.jpg IMG_0578_small.jpg
 
I finally had the time to do a bit more testing and the noise is definitely coming from the preamp section:
Yes, preamp is usually the culprit. I have a nasty static noise in the preamp section of my TA-5650 and as mentioned a hiss noise in the phono section of my TAE-8450. It is not allways the pots and switches that generate these symptoms but that is a good place to start.
I have yet to open any of my Sonys pots and switches, but from the photos you posted they look like Alps devices, similar to those in Yamaha and other Japan units. The three sction pots are probably difficult to open. I would only unsolder them off the boards and shoot deoxit from the bottom side, for now. I do not nelieve they are the source of your hiss. The selector switches you should be able to take apart. Because they are open design, they will have more oxydation that cannot be cleaned with deoxit. I would take those apart and clean them. DO NOT use sand paper or any abrasives on the contacts of these switches as you will ruin the silver plating of the contacts. There are oter methods to clean them. I prefer usnig an abrasive free eraser.

About the heat: If you verrified the v-fets with the tracer, then I wold look to see if there are and service bulletins for this model, that would adress bias adjustment. Maybe the setting in the original manual is too high???

@vintagejapan is in the process of rebuilding his two units. He will have more first hands expereince with the TA-8650.
 
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I'd love to hear about these alternative methods
I meant to say that if you open the originals up, that involves cuting the exterior heatshrink. It can be done in the area of the metal collar / mounting brace. If you go that route, see replacement caps below.

The alternative solution to cutting the originals, involves making your own dual caps...
UPW1V332MHD
https://www.onlinemetals.com/merchant.cfm?pid=4368&step=4&showunits=inches&id=71&top_cat=60

LLS1K103MELC
https://www.onlinemetals.com/merchant.cfm?pid=7054&step=4&showunits=inches&id=71&top_cat=60

https://www.ebay.com/itm/4-FEET-4-0-Black-Heat-Shrink-Tubing-2-1-Ratio-4-inch-foot-to-4FT-48-100mm/201930482835?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
https://www.ebay.com/itm/M4-PCB-Snap-in-Screw-Terminal-VERT-Pack-of-5/382126203094?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649


these should give you the ideea. If you need additional details, then maybe this DIY solution is not the best approach for you. If you do not need additional detalis, post the photos when you're done :beerchug:
 
If you verrified the v-fets with the tracer, then I wold look to see if there are and service bulletins for this model, that would adress bas adjustment. Maybe the setting in the original manual is too high???

The only servide bulletin for the 8650 I found is the one common to all the 1st series Sony vfets on how to check the vfets and replace them. I could not find anything about different bias settings/part replacement, so I set the bias to the 125mV indicated in the service manual. I made sure the bias resistors R725/775, R731, 732, 781, 782 are the correct ones for the rank of the vfets I had.

I will try to cut open a spare cap I have around in the next days, to test if I can feasibly mount new caps inside. If that works, I will try and do the same on the original ones, and I will surely post pictures.

On another note, what type of non abrasive eraser do you use? I didn't even know those things existed!
 
Stuffing two caps into the original cans might be a tough size match. Be sure to do your size searching with a careful eye. Usually when a cap is reused with a new cap it started as a single cap. Those double cap are essentially unavailable. Maybe you will get lucky. When I redid my Onkyo TX 4500 it had a double cap to start. I had to eventually replace it with two singles, but luckily Onkyo left an extra mounting hole on the chassis. Good luck on your search. I will keep watch on this thread to see how things progress.
 
I should be able to fit two 10000uF caps into the large double cap casing without too many problems: the diameter of the original case is 75mm and there are 10000uF caps that are 35mm in diameter. I am not entirely sure if two 3000uF caps will fit in the smaller of the two original cans. What I need to figure out is how to connect the leads of the new caps to the original terminals, because I won't be able to reach the inside with the soldering iron and the new caps in place. The easiest option is surely to wire the connections, but I am not sure I like that
 
I should be able to fit two 10000uF caps into the large double cap casing without too many problems: the diameter of the original case is 75mm and there are 10000uF caps that are 35mm in diameter. I am not entirely sure if two 3000uF caps will fit in the smaller of the two original cans. What I need to figure out is how to connect the leads of the new caps to the original terminals, because I won't be able to reach the inside with the soldering iron and the new caps in place. The easiest option is surely to wire the connections, but I am not sure I like that

Exactly, I am looking into that as well. The easiest thing would be to have a plastic or aluminium adapter machined with two 35mm holes in a 75mm circular body, then cut by handsaw a little gap at the narrowest passage between the 35mm hole and 75mm outside, allowing clamping action when tightening the chassis clamp. Note that the original 75mm cap penetrates the bottom chassis plate, so the new caps can be higher than expected.

I found some Panasonic GYU 15000uF/63V recently, 35D x 120H (incl terminal screws) that I will try in the near future.

GYU.jpg

Then make a copper sheet (bar) middle section between the caps for the 0V rail, with multiple threaded holes.
Pretty much as done inside the TA-N7B.

As for the dual 4700uF; the easiest might be to buy two screw type Nippon-Chemicon KMH series capacitors with individual chassis clamps, and adding a similar 0V rail in the middle again.
 
I should be able to fit two 10000uF caps into the large double cap casing without too many problems: the diameter of the original case is 75mm and there are 10000uF caps that are 35mm in diameter. I am not entirely sure if two 3000uF caps will fit in the smaller of the two original cans. What I need to figure out is how to connect the leads of the new caps to the original terminals, because I won't be able to reach the inside with the soldering iron and the new caps in place. The easiest option is surely to wire the connections, but I am not sure I like that

In my earlier post I provided you with links to the caps that would fit.
 
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Stuffing two caps into the original cans might be a tough size match. Be sure to do your size searching with a careful eye. Usually when a cap is reused with a new cap it started as a single cap. Those double cap are essentially unavailable. Maybe you will get lucky. When I redid my Onkyo TX 4500 it had a double cap to start. I had to eventually replace it with two singles, but luckily Onkyo left an extra mounting hole on the chassis. Good luck on your search. I will keep watch on this thread to see how things progress.
This was the case with a couple Marantz 140 power amps I restored. I found an extra hole and was able to mount two cap clamps without drilling any holes. I have seen some threads where the person made a mount out of flat metal or plastic. Drilled holes in it to match mounting holes in the chassis. Then a few more holes in the new mounting plate for cap clamps.
 
I have also seen scenarios where the extra cap was laid into the case horizontally. There sure does not look like there is much spare room in that Sony. I appears to be packed to the gills
 
From several measurements that I made, a lot of wiring to/from the main buffer caps to the amplifier is in general a bad thing. It adds quite some induction in the system where you don't want it.

The original TA-8650 power supply construction is already far from perfect with all its wiring between main power supply caps and amplifier boards. Building up new capacitors inside the old can, adding even more wiring to the already 'wired' installation does not seem like a good plan to me.

Making an 2x 35mm adapter puck also looks like less work than recreating the dual inside cap...
 
I got my hands on a beautiful TA-8650 that I bought broken a couple of weeks ago and brought back to life.
It's the best example I have ever come across, nobody had ever worked on it, and it was in storage for a very long time (in a very dusty place). It came with 3 of 2SK60 gone and a burnt resistor, but I had 3 spare ones laying round with the same ranking, so after cleaning it (a LOT of dust) and recappping it entirely, it was up and again ready to be tested. All the biases checked correctly, the DC offeset too, I plugged the oscillocope and the signal generator and... nothing. No waveforms at all.
After a bit of troubleshooting, it turned out it was the switches, that were still in need of more cleaning (at firist I thought one of the ICs had gone bad). After taking them all apart (what a pain), now the amplifier is back and works quite nicely.
Two things though do not seem quite right:
the first is that it runs HOT. I am used to the fact that vfet amplifiers run hot, I have already a TA-4650, two 5650, and also a TA-F7 in my collection, but this one is on another level hot: I can't really keep my hand on the top cover at all, because it just burns, although the thermistors never sent the amplifier into overheat protection for now, even after a few hours of continuous operation. Is it normal that it is that much hotter of a 5650?
The second problem is a slighlty annoying hiss from the speakers, regardless of the volume, which can be heard quite distinctly at equal levels in both channels. I assume it is a power supply issue, although I have not investigated much for now.
In case I decided to replace the main filtering caps, those in the TA-8650 are quite unique. It has two double filtering caps, one large one with two 10000uF caps inside, and a smaller one with two 3000uF caps.
As the amplifier looks pristine, I want to keep the cans of the original caps to keep the original look. Especailly for tube gear, I have seen people emptying the cans and using them to put modern replacement caps inside, but I have never done it myself. Has anyone got any suggestions on how to do that?
View attachment 1233814
I am also in a process of restoring a 8650.
The bias amount was revised from Sony and I seen somewhere on Japanese blogs that correct bias is around 25mV

I used 2x10000uf but connection with the screw was not satisfactory so will be pondering around this soon also. Maybe someone could make a kit for a group buy?

Mine has a fault on the preamp, and am pretty sure is the green Sony IC’s which are unattainable...
 
I have not seen it written anywhere no. The place I saw it was on japanese blog sites. I have biased mine on 40mV. The heatsinks get toasty hot. I think 129mV will cook the Vfets to a slow death.
 
Mine has 70-80mV without top cover, 100mV just right after top cover removed and it's not toasty hot, only 40C degree on top cover
 
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