For Boston A120s, best place to buy replacement parts. 1 of each per speaker, non polar 4.7mfd 50wv, 10mfd 50wv, 16mfd 50wv, 2.5 ohm 10%.
Figured it would be a good project to do. Any specific brands to look for, Also clueless as of to what the numbers mean.
Not sure if there is an issue, figured they are about 30yrs old so it couldn't hurt to replace them. Don't see to much info on 'vintage' gear around here.
pewternhrata
Many owners of speakers about 30 years old, believe that rebuilding the crossovers of their old speakers is a good project to do. The internet is full of easy-sounding advice on this subject. However, it also can be like opening a "can of worms".
The first advice I'd offer is,
If it ain't broke, don't fix it. I am not being facetious about this. What evidence do you have that your speakers aren't working right? What evidence do you have that the crossovers are failing or have failed?
You've already gotten good answers from Verdinut and TLS Guy for your simpler questions. Some (but not all) older non-polar electrolytic (NPE) capacitors can drift out of spec due to drying of their electrolytic solvent. It's usually a gradual process, but sometimes there is total failure due to greater leakage or a burst capacitor.
NPE caps were made, and can be still made very cheaply. Often they're made to somewhat sloppy specs. Imagine that you need two 8 µF caps, and you buy cheap NPE caps, labeled 8 µF ±10% (meaning they will be anywhere from 7.2 to 8.8 µF). You might have to buy 10 or 20 of them before you can be sure you have two caps that are actually 8 ± 10% µF.
In new crossovers for DIY projects, most builders favor using new metallized polypropylene (MPP) capacitors. These are made by rolling up a thin film of plastic coated with a very thin layer (sputtered on) metal conductor. They should never drift or fail. In the past they were less available and much more expensive than NPE caps. Now they cost a bit more than NPE caps, but they almost always measure exactly the capacitance value printed on them. Solens (mentioned above by TLS Guy and Verdinut) are good, but so are others that can be less expensive. See the Dayton 5% MPP caps sold by Parts Express, or the Bennic MPP caps sold by Madisound. Both "house brands" are made in Taiwan, perhaps by the same manufacturer.
Now on to the real question you should be asking –
will my 30-year-old speakers sound better if I rebuild the crossovers while replacing crossover components? Yes, but only if the old capacitors have drifted out or spec or have failed. Despite the common internet wisdom, there is no guarantee this is the case for your speakers. The resistors and inductors coils are unlikely to have failed. Sometimes resistors burn out, but that should be easy to see.
This also raises another bigger question. Is the 30-year-old crossover design on my speakers a good design? Or, will a new design (done by someone competent with modern design tools) actually work better? If you're going to the effort of replacing old caps, that may or may not have drifted out of spec, why not examine the old crossover design to see if your speakers would sound better with a new and different design? Why stop with crossovers? What about replacing old drivers with newer designs? This is that "can of worms" I mentioned above, getting opened. If you have to ask a simple question, such as what does mfd mean, I don't think you are ready to design a new crossover for your 30-year-old speakers.
That's why I and others are reluctant to offer simple advice to newbies about 'recapping' the crossovers on older speakers.