Legendary Audio Classics
Technics Tips and Tricks

APS-13 Page at C Crane

APS-13 Page at Manufacturer's Page

I think we should. And we can. My aim here is to provide some general tips that are aimed at electronics types. If you're not technically sophisticated, just skip this tip - you don't want to electrocute yourself, or ruin your prized Technics.

• Carbon Resistors: These components age rather quickly compared to most other components. As they age, two things happen. First, they change in value. That doesn't have to be a critical problem; A good design will put a value in there that based on the rated tolerance of the resistor itself lands dead-center in the middle of the needed value, and so there is some room for change. I think we can be confident that Technics got this right very consistently based on the observed performance of the units. Still, you should be aware of it. The second thing is that they actually get noisy. That's right - they generate noise! For this reason alone, it's a good idea to replace them if they are found in low level signal circuits, either audio or RF. Choose the replacement carefully. For audio circuits, high precision metal film resistors are great. For RF, they're terrible. This is because of the RF signal characteristic known as "skin effect". RF tends to flow on the surface of a conductor, rather than inside it. So the film resistors turn into odd-value components that also, unintentionally, contribute inductive and capacitive components to the circuit. Find a resistor type that meets the design limits - value, tolerance - that is designed for RF-neutral operation. Consult your parts manufacturer. I cannot overemphasize this issue - never use a metal film resistor in an RF signal path of any type.

• Electrolytic Filter Capacitors: These, along with carbon resistors, are the components that change the most and have the most deleterious effect(s) on the sound and performance of older audio gear. Factors that affect these parts include age, frequency of use, heat, and signal characteristics. Things that change include the actual capacitance, the internal resistance, the apparent inductance of the part, the breakdown voltage and the leakage. In short, basically everything changes, and rarely for the better. The electrolytic's dielectric can dry out, and that leads to all manner of bad things. Eventually, they will either fade away in capacitance, open, or short out, this last behavior often causing circuit damage. So these are prime candidates for a replacement program. When you replace an electrolytic, use the same value in microfarads. Resist the temptation to increase the value of filter capacitors, for instance. Why? The general answer is that the designer(s) knew what they were doing - they didn't just "put" those values there, they designed them in for one or more reasons, and in the case of Technics designs, cost was usually not the key factor. A more specific answer is as follows: If, for instance, you put in larger capacitance value power supply filter capacitors, the cold-start inrush current into the caps, and thru the rectifiers can be significantly greater than the rectifiers - and perhaps the power transformer also - were ever designed to handle. If a rectifier blows, you can cook off a lot of the rest of the unit... and you don't want that, right? In signal circuitry, the electrolytics perform more than signal transmission functions, they also are part of the inter-circuit impedances, and those can affect frequency response and phase shift, both of which can produce immediate (and annoying!) changes in the unit's ability to handle audio. Back to replacement specs; specify the same, or higher, voltage rating on the electrolytic. Use polarized parts where polarized parts were used (probably everywhere... otherwise use nonpolarized high quality caps, of course). Don't replace nonpolarized with polarized, ever and don't replace polarized with nonpolarized even if it seems like nothing could ever happen as a result - it can, trust me on this. Nonpolarized electrolytic caps tend to die if they are kept polarized one way for long periods of time. I don't know why, but I do know this to be a fact from long personal experience in repair and design.

• Potentiometers, Switches and Buttons: These get noisy because they are simply accumulating dirt and/or corrosion. When they are on one position, the surface of the contact for the open circuit or part of the path of the pot's wiper is uncovered, and it picks up debris and/or corrodes. The best cure, hands down, is a good "tuner cleaner" product. I know people who spray 3&1 oil on pots and switches. It works, but it can be messy initially, and because the lubricant leaves a tacky film, it forms the basis for future debris accumulation problems. Of course, oil being what it is, spraying again with 3&1 again fixes the problem completely for a while, and if that makes you happy... hey, do it. :-) But a nice tuner cleaner with a built in dry lubricant (like that blue stuff I can't remember the name of right now) works as well, and for longer. After applying, run pots through their full range at least ten times, perhaps more. Work switches in and out. Do all of this with the power off - it won't help to have it on, and in some cases might hurt. Speaking of power, the power switches and speaker switches are problem areas. They corrode like everything else, but because they handle so much power - high voltage and some significant current in some cases as well - they're a bit tricky to clean up. Sometimes it takes a few tries, and sometimes you simply have to maintain them at a higher rate than anything else in the unit.

• Plugs, Sockets and Relays: Just like switches, plugs and sockets accumulate corrosion and debris. Pull them, douse both the male and female ends carefully with the tuner cleaner (or 3&1) and then plug them into, and pull them off of, each other at least ten times. This "wipes" the surfaces against each other, helping to remove corrosion. The oil is a good deal in this case, because since the connectors don't have to move, unlike a switch, the oil will just sit there. It seals the surface, reduces future corrosion, and generally helps and does not hinder. This is also true of external plugs, such as RCA jacks. Don't use oil or tuner cleaner on relays. Relays need to be "dry" - the only good relay is a dry relay. File your relays using the finest file you can locate, and we are talking very fine here. This is true of any relay, but in the case of our classic amps and receivers, these speaker protection relay connections carry a lot of current and anything other than contact to contact connections will age the contact faster than it would otherwise normally age, leading to more problems.

--Ben

As an initial rule of thumb, if you series two bulbs, the bulbs will probably draw less than 1/2 of the rated operating current; if you series three, less than 1/3rd, and so on. This is generally true when the sum of the lamp voltage ratings is higher than that of the applied voltage across the whole series string. Even when that is true, because the resistance of a hot filament is nonlinear and varies with the design of the filament, you must measure the current drawn by the series string and actually verify that it is under the rating for the Technics unit. In at least one case - stereo indicators - setting up a situation where the current draw is more than the rated amount will cause damage to the receiver (destruction of the stereo decoder IC in this specific case.) So measure!

For example, recently I replaced a stereo indicator that was supposed to be 30 ma/12v with a series of two 8v/40ma bulbs. The sum of the rated voltages is 16v, so my rule of thumb that says the current draw would be 1/2 or less than the rating (40 ma) comes into play.

I put one on the indicator, and the other I mounted behind the indicator panel, inside the chassis. When I measured them, the current draw at 12v was only 16 ma, the bulb was more than bright enough, *and* the voltage across each bulb was only 6v, so they'll likely last much longer than they would if used in "normal" 8v service. As a side benefit, the load on the stereo IC's lamp driver circuit was decreased from 30 ma to 18 ma, and that IC is now likely to last longer as well.

If you're like most modern rockers, you're likely to be a fan of significantly enhanced bass. Bass is a big part of modern music. And bass from Technics gear is heavenly! Well, if you have a separate amplifier and preamplifier, and the amplifier has its own gain controls (like the 170dc, 300dc and so on,) then here's what to do:

• Turn the amp gain controls all the way up and leave them there.
• If you have control of the source volume - E.G., tape deck settings - then turn that up as far as possible without distortion.
• Finally, control the volume exclusively from the preamp.

Here's why: The loudness setting on the preamp has less and less effect as you turn the preamp's gain up. So, with the amp turned up, and possibly the source signal turned up as well, you don't need to advance the preamp gain that far to get a high output. And, with the preamp gain setting lower, the loudness contour is further engaged, hence stronger bass (and treble) enhancement. Of course, you can push this even further with the bass equalization controls on the preamp.

And conversely, if you think the loudness on your preamp is a little too much, turn down the gain on the power amp, and turn up the gain on the preamp further. It'll significantly reduce the amount of loudness compensation that the preamp applies, great for classical music or any situation where you want to hear the music closer to how it was mixed to the recording (which I note wryly is very seldom what the original artist had in mind, but does usually reflect the producer and/or engineer's vision of the final product...)

Enjoy!

--Ben