1. Home
  2. Hobby Electronics Basics
  3. Guitar amp re-capping

Guitar amp re-capping

An old guitar amp is headed my way, solid state, maybe 50 Watts, maybe a couple decades old. One reads about the finite lifetime of electrolytic capacitors, so I have some questions:

  1. What are the actual failure mechanisms?

  1. Is there a convenient way to check an electrolytic?

I don't want to replace more caps than necessary. One website suggests simply following the signals with a scope and verifying that the functioning of the circuit is consistent with functioning capacitors, and I will certainly do this, but am wondering if there are some tricks of the trade to know.

Thanks in advance!

Reply to
Bearded Occam
Loading thread data ...

"Bearded Occam"

** But how many hours has it done??

Bet it is only a tiny percentage of what a TV set usually does in 20 years.

** 99% pure bollocks.

Forget it with a SS guitar amp.

...... Phil

Reply to
Phil Allison

The electrolyte dries out.

Measure the capacitance.

Not really adequate.

Power supply caps are likely to be the main problem. Check for abnormally high ripple voltages. Also check for bulging cans and signs of leaking electrolyte.

Graham

Reply to
Eeyore

** Wrong.

One measures the ESR and compares the reading with a similar, known good electro.

A high ESR value indicates serious loss of electrolyte.

The capacitance falls only much later in the failure process.

........ Phil

Reply to
Phil Allison

I've certainly seen examples of capacitance seriously degraded as a result of the 'bad caps' issue.

Also, not everyone has an ESR meter by a long way. Any other suggestion in the absense of one ?

Graham

Reply to
Eeyore

** You can fabricate a simple ESR meter using an sine generator ( set to 50kHz to 100kHz ) and monitor the output with a scope set to max sensitivity.

Then just connect a co-axial output lead across the electro under test.

....... Phil

Reply to
Phil Allison

Nice and simple. Good call. Lacking a real signal generator, I will try it tomorrow with a frequency in the audio band, using my PC as the generator and analyzer.

Reply to
Bearded Occam

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.