Build quality: vintage receivers are solidly built. They use high quality materials (often all metal) and wood too.
Sound quality: vintage receivers often have very low harmonic distortion that often rivals modern receivers. Beyond that, the sound is often thought of as being more lifelike, dynamic, or full by some.
Repairability: a vintage receiver will last a lifetime. Literally. They require maintenance, but so do modern receivers. But often, modern receivers are unrepairable with surface mount components and other construction methods. Vintage receivers were usually built with the intention of being repaired when they break. Not thrown out.
Value: A high end, restored vintage receiver will run you between 100 an 350 dollars usually. A modern receiver with that level of sound quality is near impossible to find at that price. But a vintage receiver in need of repair will run you about 30 bucks, and can be brought back to better-than-factory condition for about 50 to 70 dollars, plus a couple hours of your time.
This Instructable serves as a basic guide to selecting of a vintage receiver and general repairs that need to be done to bring it back on line. A word to the wise: this Instructable, as I said, is a general guide. There may be questions or issues that you stumble upon specific to your receiver. RESEARCH RESEARCH RESEARCH. audiokarma.org and diyaudio.com are both great resources, but a simple google search can turn up much information. Also, try finding a repair manual on Google. If you find a free download, or even one for a couple bucks, it might just save your project from the scrap heap.
Step 1: Find a Receiver
Here, I'm going to use the rebuilding of my Sherwood S-8900 as an example. This receiver was op of the line in 1974, with a list price of $399 dollars. About $1800 today. It's well built and easy to work on. I picked it up in working condition for 30 dollars from a local antique store.
Step 2: Diagnose Potential Issues
Old capacitors: electrolytic and paper capacitors degrade with age. Paper capacitors tend to change their values, while electrolytics break down chemically and essentially turn into a resistor. When power is put through them, they heat up, boil the liquids inside, and go boom. For this reason NEVER PLUG IN AN OLD RECEIVER RIGHT AWAY. Capacitors have a shelf life of anywhere from 10 to 30 years, but a usable life of 1000 to 5000 hours, depending on application and quality. For those reasons it can be assumed a receiver from the 1970s has bad capacitors.
Scratchy controls: the potentiometers that control volume, balance, and EQ need maintenance to function properly that almost was certainly never done. Dirt collects inside of the pots and wipers and traces (depending on material) corrode. Also, the lubricant inside the pot can gunk up with use and needs to be cleaned out and reapplied. If a bad pot is turned, the audio from the speaker often crackles and pops, or even cuts out. While the effect of a bad pot is dramatic, often a cleaning is all it needs and that is easy enough.
Blown bulbs: most receivers that fall into the vintage category preceded widespread use of LEDs. For this reason, small incandescent bulbs were the source of illumination. Being incandescent, they burn out over time. Thankfully, replacement is easy if you can find a bulb, but if you can't an LED conversion is possible.
Step 3: Capacitor Replacement
As to where to order your capacitors, there is one only one place I can recommend, due to their selection, service, and prices, and that is Parts Connexion. They also have many other replacement audio components, but they keep a large stock of many audio grade capacitors that are hard to find anywhere else. And as to what kind of capacitor to order...thats an area of personal preference and hot debate. The sky's the limit with capacitor prices, and many people don't want to buy the most expensive capacitors. Some recommended brand for their sound quality and price are:
Elna Silmic II: said to have very clear, smooth mids and highs, and strong bass. Some feel the bass can be unrealistic however. This is my preferred capacitor.
Nichicon Muze Kz: said to be relatively neutral in tone, and having great clarity. Some say the highs can be harsh.
Some other brands to look into include Mundorf and Sanyo Oscon. When it comes to selecting replacements, make sure the voltage rating of the new cap is higher than the old, as well as capacitance value. But that being said, if the old cap is 250uf, the new one can be 220uf. Power caps can be upgraded to larger values, but not by too much, as it can over stress the power supply. For my receiver, there are 25 electrolytic capacitors. The 3300 uf main power cap was changed to a 4700 uf, as were the 4000uf output caps. Here I used Nichicon Gold Tune, since they are priced well and come in the required values and voltages. Some of the other power supply capacitors that were 500uf were changed to 470uf to balance out the increase of the main capacitor. These, as well as all the smaller value caps, were almost all Elnas. My bill from Parts Connexion for all 25 capacitors plus shipping was about $60.00
Step 4: Fix Scratchy Controls
Dust removal: use an air duster to spray the dust out from in the pot. Put the straw in the space by the leads and give a couple sprays. Deoxidation: use a chemical cleaner to remove any tough dirt and oxidation. For this I recommend Caig Deoxit, which is available with Caig Deoxit Gold at RadioShack. Caig products are also available at Parts Connexion. There are many types, but I recommend the airosol spray type, since it more effective at reaching into the pot.
Lubrication: this is a necessary step to preserve the life of the pot. For this step Caig FaderLube is probably the best, though I have used WD40 with success. Many hate the idea of using WD40, but if the pots on the receiver were as bad as mine the WD40 also helps break up the tougher corrosion that the Caig products did not. The lubricating properties also preserve the pot and prevent further corrosion.
When cleaning the potentiometers, they can be left in the receiver if you are able to still stick the straw of the spray in the space by the leads. Just try not to make a massive mess, and keep the pot surrounded by paper towels so the spray does not end up coating the inside of the receiver or circuit boards.
Step 5: Replace Bulbs
The LEDs should usually be wired in series with a resistor, since the voltage supplied to them by the receiver can be around 12 volts. You can also figure 3 ultrabright LEDs to replace one bulb and ensure they are equal or greater brightness. However, when it comes to figuring out the number of LEDs and resistor, it's up to the stats of your receiver, making it hard to provide specific instructions. Often, by googling the type of bulb used in the receiver, the specs of the bulb allow you to determine the voltage that will be suppled to the LEDs. You can also just measure the voltage being supplied to the socket with the receiver switched on.
When replacing the bulbs with LEDs, also try to preserve the connections for the bulbs so if you ever want to go back to bulbs it is possible without too much extra work.
For my receiver, the bulbs were GE53, which is a 14v bulb. I smashed the glass of the bulb and soldered the series resistors and LEDs to the filament support wires in the bulb. The space in the bulb was then filled with hot glue. This allowed the LEDs to be inserted into the stock bulb sockets. Blue LEDs were used to light up the glass, green for the FM signal dial, and red for the stereo light. Since my bulbs are bayonet base, it's important to make sure that the LEDs face the right way when the bulbs are rotated and locked into position. The LEDs are powered of AC, which the LEDs I used can be powered off of safely. Some LEDs have poor reverse polarity strength, but the LEDs I used are the high dispersion type from Christmas lights, which also handle reverse polarity well. Some receivers, however, for things like stereo lights used DC electricity, so heed the polarity. My stereo light operates on DC, so the LED had to be soldered on with the polarity correct.
Step 6: Finishing Touches and Use
Now it's time to use it! It's a good idea to power the receiver on with the case apart, and leave it one for a couple minutes. This is just incase you installed a cap backward, and it bursts, you don't have to tear it apart to replace that cap (it's happened to the best of us). Also, many feel that caps have a break/burn in period, others do not. The Silmics have incredibly strong bass immediately after installation, and it is my experience that this does recede with time; so don't judge the sound immediately. Break in can take up to 40 hours of listening time.
My results were exceptionally positive. Over my old 1990's Pioneer receiver, the sound is much more full, with bass that is cleaner and more controlled. Highs don't screech, but they aren't mellowed out too much either. The mids are very clear, but don't shout on complex music like the Pioneer did. Plus, the silver front and glowing blue tuning dial look retro but not outdated. For 90 bucks, it can't be beat!