[charmerci]

I've never had a detail oriented memory so my question is, iirc, old capacitors (?) end up being... not good. They often should be replaced.


What happens? The internal chemicals evaporate? Why is leaving them in bad? How does it affect the sound? I'm assuming that the component is perfectly playable but just sounds bad.

[Mike B.]

Film caps and resistors can still be OK. Electrolytic caps are the first items to be replaced IMO. Pots and contacts should be sprayed with a cleaner made for electronics. A visual inspection of the individual components for any deterioration or burning is advised also.
Sound should become more dynamic and focused with those changes.
This is just a rough idea of how to approach older units that have been in storage or unused for long periods.

[poseidonsvoice]

I've never had a detail oriented memory so my question is, iirc, old capacitors (?) end up being... not good. They often should be replaced.


What happens? The internal chemicals evaporate? Why is leaving them in bad? How does it affect the sound? I'm assuming that the component is perfectly playable but just sounds bad.

Over time, let's say 2 decades or 20 years, it's a good idea to replace capacitors, particularly electrolytics in a power supply. The enemy of a capacitor is moisture. When condensation occurs within a capacitor, then it starts getting leaky. This means that the original job of filtering out the AC ripple because more faulty. Which means that you start having AC ripple (60Hz hum) from the power supply get into the circuit.

In a coupling cap, which is usually a film cap (non electrolytic) the same can occur. For example in a tube circuit there are many designs where a coupling cap is used between the 1st stage (input driver stage, plate of the tube) and the output stage which is usually the grid of the output tube (let's say a 300B). The coupling cap in this situation allows the AC signal (music signal) to pass through but should eliminate all DC. The plate of the 1st tube might be at say 200V DC. The grid of the output tube should be at 0 volts IF the coupling cap is working as it should. As soon as you see a few volts of DC on the grid of that output tube, it's time to replace the coupling cap. Coupling caps over the years have definitely improved in design, and are also smaller. Check out an old Dyna ST70 and look at the coupling caps. They are huge for the value needed. Modern designs are more compact and more insulated as well.

I am sure there are countless other examples, but you have to remember these electrolytic caps and coupling caps are under strain and stress. They only have a finite life span and can only survive finite temperatures as well.

The way to discover these issues is to have a good understanding of electronics, and also own a volt meter or oscilloscope.

I strongly recommend you watch Uncle Doug's Videos with regards to Coupling Capacitors, Parts 1-3. He also has videos on resistors, transformers, etc...He was a science teacher back in high school and he definitely has a talent for teaching even the most mundane of subjects.

Start here:

https://www.youtube.com/watch?v=l-u8J-yh9ZA

Best,
Anand.

[charmerci]

Thanks, Anand. It'll take me a while to digest this.

[Speedskater]

Film capacitors made by a major capacitor manufacture in the last 4 (or more) decades should last a century.
The exceptions would be over voltage or over heating.

[poseidonsvoice]

Film capacitors made by a major capacitor manufacture in the last 4 (or more) decades should last a century.
The exceptions would be over voltage or over heating.

Indeed. Most of the failures I have seen are in 1950’s to 1970’s tube amps using Sprague film caps or similar. The carbon composition resistors get noisy too.

Many are in warm/hot environments.

Best,
Anand.