Recycling audio gear
Notwithstanding the notes made in respect of recycling redundant equipment to make 'new' test gear, it is acknowledged that every time an item is repaired it is being recycled. Take houses, cars or jewellery as an example. Judgements must be made whether it is indeed economical to effect repairs. For example, a lightning strike can stress equipment that can appear to function normally at first, but later is prone to a series of failures that are not economical to proceed with, beyond a certain point. In some cases, as with fire say, it will be obvious that an item is beyond use and salvage. On other occasions it may not, as witnessed by the time, trouble and litres of WD-40 used to attempt to save the studio that sank with the house-boat it was on.
Sometimes one gets lucky, or with a bit of perseverance results are obtained that justify the effort made. Often items are discarded by an owner who considers repairs unaffordable, which however are to one who is happy to spend a bit of time and trouble. A wide-screen Hitachi TV was dumped because of dry joints on one of it's electrolytics. A Marantz PM-54 amp (considered 'nice' by many) was found in a skip, it's only problem being a cracked and open-circuit mains fuse holder. One friend was insistent that a Bush Arena TA2800 tuner amp (1972) was 'dead' and fit only for the bin. This had a nice (for it's time) radio and a cheap 'Sun' brand of electrolytic (all 10µF) had gone open circuit with age (a common feature of 'Nashville' caps). These were replaced in an evening. A Pioneer SA-420 amp was similarly binned with blown indicator lights and a Kenwood RD-M23 CD receiver with intermittent display light connector. All of the above are still working well today and are used together with a pair of Castle Kendal II speakers that had paint tipped on them. All now look and sound fine and were used with the computer that was used to compile these web-pages and their graphics, which had been thrown out, 'rescued' and finally gave up the ghost after more than seven years of continuous use!
A discarded Samsung projection TV, built in September 2003, whose screen was smashed yielded (apart from filter and power supply components, sockets, screening cans, amplifier modules and heat-sinks) a rather nice speaker system upgrade for some bookshelf speakers. The deflection amplifiers, in two modules each with three amplifiers (STK392-010), were converted for audio use (driving two 2-way full-range speakers and a sub-bass unit). The chipboard chassis was composted and the plastic case parts recycled.
Occasionally requests are received to improve equipment's performance. Sometimes this is possible and sometimes not. Many moons ago, a friend asked if his very cheap Amstrad amplifier could be improved and, as a joke, it was accepted. Mains wiring was rerouted, the preamp transistors were replaced with low-noise types, a novel screen (aluminium foil backed Fablon) covered the preamp and selector switch, and the main smoother was increased in value. For decades later, the friend was extolling the virtues exhibited in effecting a 'miraculous' improvement in performance (in real terms noise was down by >10dB).
Old equipment is often capable of good performance, and since it is relatively difficult to transform an item's function, say from a toaster to a television, it can make sense to improve an item's performance simply by using modern components. Electrolytic capacitors, perhaps the least reliable electronic component, are a case in point, these probably being the one component whose uprating produces the most tangible results, most easily. A modern replacement in the same can size can accommodate values two or three times higher than older types with superior voltage and temperature ratings. Valve designs in particular can benefit
Similar claims can be made for output transistors, modern faster (by 5-30x) and higher gain types outperforming their older and slower counterparts, improving the high frequency performance of an old design by a considerable margin. In some cases, or with little modification, V-FETs can directly replace Darlingtons. Reducing the gain of a power amplifier, even by a small margin which isn't subjectively noticeable, will improve high frequency performance and reduce the noise floor. Replacing input transistors for newer low-noise types and older carbon resistors in feedback networks for metal-film types can also improve.
When asked to replace a combo's burnt out mains transformer and/or speaker, a more powerful replacement is offered as a matter of course, given the constraints that budgeting puts on commercial designs. Invariably, improved performance and sound quality is reported.
Many designers, and not just those in consumer electronics, have been appalled to see their very excellent original work bastardised by budget-driven production teams. If one has a favoured amplifier, say, one has the opportunity to redress the balance.
Modifying an existing design presents advantages to a constructor in that there is less hardware to design, make and assemble, and an aesthetically pleasing external appearance can be retained. However, constraints in an original can impose limitations, eg;
although in this case TO220 or TO3P packaged devices could replace TO3-style output FETs. Nick Whetstone's approach to upgrading the Arcam A60 amplifier might prove useful and Bernd Ludwig's excellent mods to the Quad 405 (1999) are definitely worth a look.
One design was modified by making a piece of strip-board, carrying new opamps, other components and off-setting controls, that then plugged directly into the two sockets of the original ICs on the PCB, redundant items having been removed.
Surprising has been the emergence of markets for 'antique' gear, belt sets for extinct tape recorders even being available. So perhaps instead of 'binning' those old speakers with torn cones, the price of equivalent replacement units could be determined, and maybe the need for a bit of bracing! Somebody out there might want them, even if you don't.
Firstly establish your aim. Make this as reasonable, or feasible, as possible. Before attempting to restore any gear, first obtain any service data, circuit diagrams or schematics relating to that model. Data on subsequent models can provide details of improvements that could be incorporated at the same time. Restoring to original condition with original components can suit display standard needs but may conflict with functional considerations. Often a need to retain original cabinet features is desired. Improvements, like additional external heat-sinking, may then either not be possible or required.
Original or obsolete components may be impossible to source or may in themselves cause concern having been of an inadequate quality in the first place, especially by current standards. Notwithstanding the stress they will have undergone in a normal (or abnormal) service life, age will deteriorate any given device's specification. Oxidation via the packaging will figure, aluminium TO3 cans are an example, the 'drying-out' of electrolytic capacitors is another. Exact replacement values of the latter may not be available, but given that the tolerance of original types would have been some -20% to +50% this may not be critical. Some types will fare better than others according to their method of construction. However, it can be assumed that invariably because commercial grade is involved the design life of the equipment was probably a maximum of five years, if that.
Multi-way switches or push-button banks can be troublesome if direct replacements are not available in that if disassembled a large number of connecting wires will have to be removed, their positions being carefully noted first. Some push-switch bodies are glued or welded together and a method will have to be devised to pry the two halves apart without causing damage to the internal contacts. If this level of detail is being undertaken, prior to disassembly thought could be given to electro-plating the worn contacts (often silver-plated brass), preferably with gold. Mechanical devices can be delicate so ensure that your skills match your expectations otherwise a perfectly serviceable and irreplacable component may be ruined unnecessarily.
The same applies to noisy potentiometers. Some values may be difficult to find, like say a dual 1M log/antilog, or there may be mechanical issues. In some cases, the use of a good quality switch cleaner may suffice. Lubricants like WD-40 can appear to help in the short-term but can attract and retain noisy contaminants. Jim Lesurf, formerly of Armstrong, says "It is often possible to cure this by spraying a suitable contact cleaner solution into the potentiometer whilst operating the control a few times. To do this you need to disconnect the set from the mains and remove the case as described above. I would usually recommend an aerosol cleaning spray that does not leave any residue. However in cases where this does not work you might consider trying (at your own risk!) a procedure that Armstrong used to employ back in the 1960's. This was to spray a tiny amount of light oil into the potentiometer. This lubricated and softened the surface and reformed a smooth track. However this method is “kill or cure” and may ruin the potentiometer, so only try it as a last resort before deciding the control has to be be replaced! Also, take great care not to drop oil elsewhere in the set!"
The next least reliable components are electrolytic capacitors. Upgrading to a high frequency, high temperature type (105°C compared to, say, 85°C) will definitely have a beneficial effect as will the increased capacity of modern equivalents, although care may have to be taken in terms of the increased current peaks in a smoothing array. In older amplifiers the inclusion of a mains soft-start can reduce power-up stresses on supply components, like the transformer, and speaker 'thumps'.
'Laying up' gear
If electronic or electromechanical equipment is to be stored for a long period, taking some simple steps can assist in the reduction of deterioration with time.
One of the easiest ways to stress gear (thermally) is to store it in an uninsulated roof-space. Consider the summer and winter peaks and troughs and the temperature swings that can occur over just one 24 hour period. Components least likely to survive these for long are electrolytics, germanium transistors and ICs of commercial grade. Try to store at a constant temperature, say between 5-25°C. Cellars can be ideal but may be prone to damp or flooding.
Thought can be given to the cleaning and lubrication of the internal arrangement, switches, etc, the fumes from which can aid resistance to moisture if the item is then sealed in a plastic bag. For long term storage, nitrogen can fill this. Thick dust can be removed first with a paint-brush (½" or 3") and vacuum cleaner. Tropicalisation can be considered, eg; varnishes, desicant sachets, etc.
Where possible, drive belts can be removed and packed with the unit thus reducing stretching. A wise packer will include one or more new replacement belts or styli, valves, service manual, schematic, etc, which, at a later date, may not be readily available.
If no original packaging exists, thick bubble-wrap or a box filled with polystyrene chips is recommended. Don't forget to label the outside.
Sometimes long storage times can affect electrolytic capacitors adversely although a simple precaution can resolve this. The Al oxide layer may deteriorate when stored without an externally applied voltage, especially at higher temperatures. Since there is no leakage current to transport oxygen ions to the anode in this case, the oxide layer is not regenerated. The result is that a higher than normal leakage current will flow when a voltage is applied after prolonged storage. As the oxide layer is regenerated in use, however, the leakage current will gradually decrease to its normal level. Quality Al electrolytic capacitors can be stored voltage-free for at least 2 years, and long-life types for as long as 15 years without any loss of reliability. Provided that these storage periods have not been exceeded, the capacitors can be operated at rated voltage directly after being taken out of storage. In this case, reforming of the oxide layer is not required (this is normally achieved by running the capacitor in series with a 100R resistor for an hour). When designing application circuits, attention must be paid to the fact that the leakage current may be up to 100 times higher than normal during the first minutes following the application of power. When the capacitors have been stored for more than two years, it is decisive whether the circuit will tolerate high initial leakage currents. A circuit that has been stored for more than two years with the capacitors incorporated, should be operated trouble-free for one hour. This will usually regenerate the capacitors so far that storage can be continued. When applying power to a unit stored for some time, running it in series with a 60W light bulb for an hour or more can prevent failures.
This kind of effort will be immensely appreciated and repaid with interest when after ten years or more the equipment is unpacked and looks and works perfectly first time.
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