You can test them in circuit using an ohm meter.
The only problem is that you may run into occasions
where the surrounding components cause a false reading.
Then you will have to disconnect one lead in order to
check them. If this amp is fairly old you may end up having to reccap the unit. (electrolytics only) This is something I have
had to do many occasions to older equipment to get rid of
all the little problems that weak caps can cause.
Good Luck.
The only problem is that you may run into occasions
where the surrounding components cause a false reading.
Then you will have to disconnect one lead in order to
check them. If this amp is fairly old you may end up having to reccap the unit. (electrolytics only) This is something I have
had to do many occasions to older equipment to get rid of
all the little problems that weak caps can cause.
Good Luck.
Hi beppe61,
The only true way to test a cap is out of circuit with an LCR meter that also measures the real resistive portion too. You can get an idea by using an ESR meter. If the cap goes short, an ohmmeter may help. In any case, you need to lift one leg to be sure you are measuring the cap and not the circuit.
No completely easy way out, but why should there be?
-Chris
The only true way to test a cap is out of circuit with an LCR meter that also measures the real resistive portion too. You can get an idea by using an ESR meter. If the cap goes short, an ohmmeter may help. In any case, you need to lift one leg to be sure you are measuring the cap and not the circuit.
No completely easy way out, but why should there be?
-Chris
Thank you so much Sirs for the very kind and valuable advice.
To be fully honest I have to declare my almost complete ignorance in electronics.
Nevertheless, established that old (and of bad quality) electrolytic caps are weak points in old equipment I would like to kindly ask you the following other question:
- Which are the effects of a dried electrolytic cap in the two situations
1) in series with the signal (coupling cap) and
2) working as a filter cap in a power supply?
I need you an explanation anyway.
I read that a dried cap in the feedback loop between the resistor to ground and the ground could cut the low frequencies (i.e. weak bass response).
I read that a dried filter cap in the power supply could lower the peak current delivery from the amp itself.
Are these senseless statements?
Thank you so much because these are quite interesting topics for me from the moment I decided to play with some vintage amps.
I hear you: "Go to school and study !" eh, eh.
Thank you sincerely again for your great support.
Kind regards,
beppe
Torino
Italy
To be fully honest I have to declare my almost complete ignorance in electronics.
Nevertheless, established that old (and of bad quality) electrolytic caps are weak points in old equipment I would like to kindly ask you the following other question:
- Which are the effects of a dried electrolytic cap in the two situations
1) in series with the signal (coupling cap) and
2) working as a filter cap in a power supply?
I need you an explanation anyway.
I read that a dried cap in the feedback loop between the resistor to ground and the ground could cut the low frequencies (i.e. weak bass response).
I read that a dried filter cap in the power supply could lower the peak current delivery from the amp itself.
Are these senseless statements?
Thank you so much because these are quite interesting topics for me from the moment I decided to play with some vintage amps.
I hear you: "Go to school and study !" eh, eh.
Thank you sincerely again for your great support.
Kind regards,
beppe
Torino
Italy
Hi beppe,
Electrolytic caps can fail with effective resistance in series and / or parallel with the capacitance. In coupling applications, thedefective cap may allow DC current to "leak" through. This can affect the DC bias of the following stage. If it's a filter, this may lower the DC voltage (as in bias supply).
A failing capacitor across the DC supply may conduct current, causing the part to run warm and draw power. The reduced capacitance and increased resistance act to make the capacitor become less effective, or "disappear" from the circuit.
Electrolyte may leak out of the part in both cases.
-Chris
Electrolytic caps can fail with effective resistance in series and / or parallel with the capacitance. In coupling applications, thedefective cap may allow DC current to "leak" through. This can affect the DC bias of the following stage. If it's a filter, this may lower the DC voltage (as in bias supply).
A failing capacitor across the DC supply may conduct current, causing the part to run warm and draw power. The reduced capacitance and increased resistance act to make the capacitor become less effective, or "disappear" from the circuit.
Electrolyte may leak out of the part in both cases.
-Chris
Hi beppe,
This is a very quick an easy test. If you remove this capacitor, the gain of the amplifier should fall to unity (X1).
-Chris
This will cause the low frequency response to roll off higher. To test this, apply a 1kHz tone and measure the output level, change this frequency to 100Hz and go down from there while watching the level. When you reach about 70%, that indicates your -3 dB frequency.
This is a very quick an easy test. If you remove this capacitor, the gain of the amplifier should fall to unity (X1).
-Chris
A 15 years old amp used once in a while in home environment is not an age really. Caps will last longer but if they are warm or even hot they can last about a year in harsh applications. My guess is that after 10 years you can suspect something and after 15 most caps are rather functional but 20 years or more may be a lottery. Notice I'm not talking about hot tube amps.
If the smoothing is gone you will get a huge hum if the amp will work at all.
The "thin-ness" may also be a design feature. The amp has maybe never been able to reproduce low frequence's.
If the smoothing is gone you will get a huge hum if the amp will work at all.
The "thin-ness" may also be a design feature. The amp has maybe never been able to reproduce low frequence's.
Dear Mr. Peranders,
unfortunately I cannot attach any file to a private e-mail.
I would just like to ask you this anyway.
There is no coupling cap at the input of the amp.
In the feedback loop there is a 47uF/100V electrolytic cap to ground.
It would be better to change it to a 220uF or even 330uF?
Could the bass response improve ?
Thank you so much indeed.
Kind regards,
beppe
unfortunately I cannot attach any file to a private e-mail.
I would just like to ask you this anyway.
There is no coupling cap at the input of the amp.
In the feedback loop there is a 47uF/100V electrolytic cap to ground.
It would be better to change it to a 220uF or even 330uF?
Could the bass response improve ?
Thank you so much indeed.
Kind regards,
beppe
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