Recapping old HiFi equipment from the 80's.

 Hello and welcome to WhatIsHiFi blog.

After recapping a NAD 3020B, time has come for some more equipment maintenance.

Sansui A-700 & T-7, Philips CDR 950; a secondary system for background music.

For these equipment, I didn't go for full recap. My target was to extend the life of these vintage equipment, so I choose to replace the caps that are at the power supply; if these caps fail, this will almost certainly cause some damage. Also, since these equipment are used in secondary systems (not for critical listening) and they are not something extraordinary sound wise, I decided to change the capacitors that are in the signal path when possible just for the fun of it, meaning when they are at a physical position easy to reach. However, our experience shows that these capacitors do not suffer; changing them is just a precaution or a hope that a new and better type of a capacitor will cause some sound improvement. This hope is however lower, when the manufacturer has already used a bipolar capacitor of a good brand.

Before I proceed with the mods, let me share some general thoughts regarding recapping Hi Fi equipment. We have found caps at 90's amps to be OK (Luxman M-03). We have found that the Nichicon power capacitors at a 1983 Sansui Z-9000 receiver were totally out of specs, while Nichicon signal capacitors at the same receiver were pretty much OK, defying aging. Eventually, an electrolytic capacitor will need replacement but we don't know when or where. Also, we don't know the effect an old capacitor has at the sound. To make a long story short, don't get hysterical regarding capacitors. Just keep in mind that capacitors involved in the power supply need to be healthy, otherwise you might jeopardize your equipment.

Also, changing capacitors will most probably alter the character of the sound of the equipment. I was discussing this with a friend who is at the HiFi and speaker repair business for some decades now (and he is 100% down to earth with HiFi), and he told me that back in the 90's when he had a Pioneer A-07 amp, he got the best super duper Nippon Chemi-Con for audio capacitors he could find and replaced the original 4 big power capacitors that this amp had. After that, the amp was sounding a bit on the bright side. Thinking that this might be just his idea, he installed the original capacitors back; this way he confirmed that at that system he had, the sound was better with the original capacitors, event though they were "inferior". Please mind that I wouldn't expect the sound to change by changing the capacitors at this particular position but it did; so, think what happens when you change caps at the signal path. So, once more, don't get hysterical regarding capacitors. Ideally we would need to try various capacitors at various positions at an amp one by one and see what happens but this is not very practical.

As always, one of us would see the actual capacitor on the board and with the aid of magnifying glasses would read the values (including temperature), put a mark on the top of the cap (so we know with which caps we are "done") and the other would search at the schematics what is the role of the particular capacitor and order the optimum replacement. Since sometimes the replacement capacitor is not an exact match but a better one, or there are multiple types of caps with same values, you better keep notes of  what you actually order and the position you plan installing it; at some bigger projects we didn't and it took more time to find out what goes where than actually replacing the cap. If you order from Mouser, you can include the position of each capacitor in your order and they will come in separate bags with this position printed on the label. Other trusty on line sources for capacitors (except your local store) are TME and Digi-Key.

On choosing the capacitors you will use, I suggest you to go for a good brand like Nichicon, Kemet, Rubycon, Elna, Vishay or Nippon Chemi-Con. For the ones used in power supply rails, you need low ESR models. For ones used in power supply rails but directly related with the sound (like the big caps that feed the power amp section), it is logical to go for audio capacitors. For caps in the signal path, you better use bipolar / MUSE electrolytic caps or film / WIMA caps - the film ones have 10% tolerance compared to 20% of electrolytic. If you go for different type / higher voltage / higher temperature capacitors (the benefit of generally installing a higher voltage or a higher temperature capacitor at positions that get heated, is that it will almost certainly live longer), make sure they will physically fit; however, if you are replacing old caps, it is nice to know that new caps are much smaller in size. Same thing is to be considered regarding increasing the capacitance of caps used in the power supply, plus understanding if the bridge rectifier is capable to deal with the increased power demands of initially charging the beefier caps when you turn on your equipment.

Look how smaller in size capacitors have become; the one on the right has bigger capacitance and still is smaller in size.

Sometimes, you will have to make decisions (actually decide what is the best compromise) based on availability and physical space available; for example, choose between audio caps 4.700 μF or low impedance 5.600 μF.

So, let's start with a Sansui A-700 amp from the 80's.

My unit did not had any signs of leakage or misbehaviour, but none the less, I wanted to preserve it.

Sansui A-700 inside view from top.

It is so helpful when you can also take off the bottom cover.

After opening it and having a look at the physical construction and the schematics, we decided that we will go for just 5 caps, all related with the power supply at the main board 4777. Unfortunately, probably for cost related issues, there are quite a few vertical soldered sub-boards that need to be disassembled in order to change caps at the signal path or at secondary power supplies.

This board structure is making repairs somehow difficult.

To be honest, I don't mind for not changing caps at the signal path; as I mentioned earlier these caps usually do not suffer and I don't have any expectations regarding how to make the Sansui a reference sounding amp. I am already happy with the way it plays. However, since input selection is made with IC chips, I would change the caps related with this chips just as a precaution to protect them. If these chips fail, I don't have a clue if I can or if it is worthy to repair this amp.

To make a long story short, this is what we did:

- Big electrolytic caps: Amp originally had 2x ELNA 4700μf, 56V, 85°C. Since these caps are at a 46.8V rail, we decided to go for increased voltage caps so they will last longer. We choose to replace them with Nichicon Gold audio caps, 4700μf, 63V, 85°C. If we could find same type of cap but with a slightly bigger capacitance, we would go for it, but at that time we couldn't find any. These capacitors also had "glue of death" that is notorious for oxidizing nearby components and / or becoming conductive over time, so after removing the original capacitors we cleaned it.

"Glue of death" leftovers, can be cleaned with some alcohol & cotton swabs. Notice the green oxidation on the right side of the right capacitor base.

- C4 & C5: Factory caps where Nichicon 220μf, 25V, 85°C. These were near a bridge so we decided to go for 105°C. Also, we decided to increase the capacitance. We choose low impedance Nichicon 330μf, 25V, 105°C. 

- C3: Sansui had an ELNA 4,7μf, 50V, 85°C. This cap is related and sits near the STK so we decided to stick to original capacitance value but go for 105°C. We choose a Nichicon 4,7μf, 50V, 105°C.

Since we had the old caps out, we were curious to measure them. It seemed that the only caps that needed replacement where the ones at position C4 & C5. The others where pretty much OK. A good question is if a sound quality improvement was achieved by changing these caps but I am afraid that I can't answer this question. You see, this amp drives two old Sansui speakers; understanding and respecting it's class, everything was already sounding OK.

Since the amp was on the bench, we put some appropriate spray at all the potentiometers and the speaker / power button. Note that the power button actually pushes internally three switches; one for the main power and two other for the L + R speakers, so it mutes the amp when you turn it on and off. If occasionally you loose sound form one channel, you might find the cause of this here. It is good if you also put some appropriate spray at both speaker switches; in this amp if you connect two pairs of speakers, these speakers are driven in series, so the sound passes always through both the speaker selector buttons.

When you press the power button, actually you are pressing three physical switches.

Note that the Tape 2 input is the only input that is controlled with a physical switch. In my unit, quite often one of the two channels was muting and I couldn't figure out why. Eventually this was caused by the Tape 2 switch. Some contact spray and some grease between the switch and the input select button solved the problem.

Also, in the past I had problems with the loudness button which eventually broke down. Thanks to Panos, we found and installed same kind of switch from ALPS.

Last but not least, older equipment like this amp often have an input voltage selector switch, with a 220V / 240V choice. But what happens if you live at an area that has 230V AC? You can choose optimum position after reading this older post.

Dec. 2024 update: The STK4913 at my Sansui A-700 decided to give up. Suddenly, from the right channel there was a pretty loud hum kind of noise; luckily I was near the amp and I turned it off fast enough, so the speaker was not fried. This is a first lesson, this amp should not be left unattended. From the start I had a feeling that it was the STK, but in order to be sure I took an old pair of headphones and confirmed that the noise was independent from the volume knob and was there, even after disconnecting signal cables coming to the power amp board. After carefully removing the STK (some attention is needed in order not to harm the rails at the old circuit board) the noise was gone. I also checked that the STK was receiving the correct power voltage and that this noise was not coming to the STK as a signal for amplification from an earlier stage of the power board. 

But now what? As you also probably know, Sanyo is not producing any STKs and there are quite some funny stories concerning aftermarket ones. After asking my tech guru, I bought a new one from here (located in Greece). After a couple of days the part arrived, it was installed and voilà! The amp is alive again. I can not spot any difference regarding audio quality but I have to say that this secondary system is not used for critical listening, neither is revealing.

Now, let's move on with the Sansui T-7 tuner. This device is not something special but I find it very appealing that although it is an analogue tuner, it has a motorized auto search function; I always admire the electromechanical technology of the past.

You don't see these buttons often at an analogue tuner!

You just press a button and the tuner goes to the next radio station. In contrary to Yamaha T-7 tuner however, the Sansui T-7 does not have preset memory function.

Sansui T-7 inside view.

Construction of this tuner is very friendly to repairs / mods, since it opens both from the top and the bottom and has no vertically soldered sub-boards. 

So nice that you can easily remove the bottom cover!

We decided to change every cap at the power supply board F-3439 as well as the power supply section on the left of the main board. Having noted that the left side of this tuner gets warm, we decided to go for 105°C. Also, we located and decided to change all caps at the signal path, except the C47L & C47R that where already film capacitors from the factory. Let's sum up:

- C5 & C6: The original ones where Nichicon 470μf, 35V, 85°C. We replaced them with Nichicon 560μf, 35V, 105°C.

- C7: It originally had Nippon Chemi-Con 220μf, 35V, 85°C. We replaced them with Nichicon 330μf, 35V, 105°C.

- C8: It had Nippon Chemi-Con 47μf, 16V, 85°C. We replaced them with Nichicon 47μf, 25V, 105°C.

- C9: The original ones where Nichicon 100μf, 16V, 85°C. We replaced them with Nichicon 100μf, 25V, 105°C.

- C11: The original ones where Nichicon 220μf, 35V, 85°C. We replaced them with Nichicon 330μf, 50V, 105°C.

- C12: The original ones where Nichicon 220μf, 16V, 85°C. We replaced them with Nichicon 220μf, 25V, 105°C.

Since we had taken out all the old capacitors, we measured them. All where perfectly OK proving that the perception that caps do necessarily age is not very accurate. Also, as you probably have observed we have increased the capacitance of the power section. Before changing the capacitors, every time I was pressing the up or down button and the motorized tuner started the auto tuning function, I could observe a small momentary dim at the display. After changing the caps and increasing the capacitance, this phenomenon did not change. I guess a fancy cap will not surpass the original design of a unit. So, I might have not regretted changing the caps, but it turned out that it was not necessary at all to do so.

Another good thing you can do for this tuner is to put some oil at the mechanical moving parts and resolder the base of the power on / off switch; mine decided to crack at the welding with the power board right after we finished recapping, making us wondering what has gone wrong.

For international buyers looking forward to get a Sansui T-7, this model can be easily internally adjusted for 110-120V or 220-240V.

Last but not least, a few words about a Sansui T-700L tuner. I wanted to recap it, but the internal construction has solely these vertical boards so I gave up even trying it. Apparently, after what we saw with the T-7 tuner I am pretty sure that the caps are still in a perfectly good state. However, one issue that it has is that it looses the memory presets if you unplug it for mains. This is an easy fix, you just need to change the battery. Since we did not have the right tools for soldering directly a new battery, we preferred to add a battery compartment; just have a look at the photos below.

This is the original battery, near it there is also an option / empty position for a super capacitor.

We installed a battery base compartment, now we can easily change the battery.

So, that was it; we had a good time preserving some entry level equipment from the past. Even though they are not anything spectacular, I find some charm in them.

Retro style, warm nostalgia.

We verified again that caps in Hi-Fi do not necessarily age. We also practically saw that if a design / power supply is weak, a fancy beefier cap has secondary role. I guess you can't beat a good circuit design just by adding better ingredients!

Regarding sound quality, as you understand this is a secondary system. I can't say if and what effect new caps had in sound quality. For a secondary system, sound was and still is pleasant.

Happy listening as always!

Christos