How can I understand if it is time to replace capacitors?

[beppe61]

Dear Maurizio,
thank you again for your always kind and appreciated reply.

You say: "May I suggest that you address your source first?
Good luck
Mauricio [/B][/QUOTE]

Well I have to tell you that I have tried a different power amp in my system (two english Albarry monos, don't know the model) leaving all others things equal.
The bass was very much more powerful and the sound seemed more developed and complete.
These monos are specified at 45W/8ohm and 90W/4ohm, and this should tell something about their current delivery.
That said, someone told me to try to replace the almost 30 years old caps with something new and above all suspicions, increasing also the total capacitance (as I said my idea is to double it).
All in order to get a little more body in the sound.
I have taken a look to the transformer and it seems quite powerful.
The diodes are discrete and quite bulky.
So I am thinking about two 15.000 uF/63V new caps of the like of Sprague, Mallory, Sangamo, ecc.
I will see in the next days.
They usually don't come cheap and I will have to shop around to find a nice price.

Thank you very much again for all your very kind support.

Kind regards,

beppe61

 

[Tweeker]

The reason I suggested 2 capacitors per rail is that for a given cap you get near half the esr and esl. Sometimes its even cheaper to boot. But, if its a hassle and you would have to tear stuff up to install them, it would be ill advised.

 

[beppe61]

Dear Sir,

thank you very much indeed for you kind and helpful advice.
Let me quote you hereunder:

>

The reason I suggested 2 capacitors per rail is that for a given cap you get near half the esr and esl.

I see very well your point.
What I am trying to get is just a little more bass response.
Anyway I am not sure that a recapping could give that.
I will never know until I try.

> Sometimes its even cheaper to boot.

This is very interesting indeed.

But, if its a hassle and you would have to tear stuff up to install them, it would be ill advised.

Thank you so much for your kind advice.

Kind regards,

beppe61

 

[beppe61]

Dear Friends,


at the end I did it today.
I have replaced the two almost 30 years old Sprague 7200uF/50V capacitors with two new Rifa 10.000uF/63V of the PEH 200 series.
I have chosen these caps above all for:
1) size compatibility
2) good specifications
3) reasonable price.
I have given up the idea of using two huge Siemens Sikorel 15.000uF/100V for size problem (just for the moment anyway).
They are sly in a box, resting and waiting for their turn.
Straight away I do not have any particular problem to report (no noise, no smoke !).
Hopefully I did not make any mistake in connecting them !
Unbelievable.
It seems that the diodes have withstood the bigger current draw at the start up.
I do not want to be too much optimistic but my impression after just two hour of listening are quite positive.
Less noise and ... more powerful sound on the bass (my inmost goal).
Before go out in the garden shouting: "Victory, victory !!!" I think it is better to wait some days of burn-in.
If I seem too much enthusiastic about this simple "operation" just think this is my very first time !
I have used this old amp to assess the influence of filter caps on the overall sound.
I will report my opinion after two weeks of burn-in.

I take the opportunity to thank all of you for your extremely kind, friendly, patient and very valuable support and advice.
Thank you.

Kind regards,

beppe61
ITALY

 

[PB2]

Hi beppe61 hope things are good with you,

I'm a bit late here but I wanted to mention a few things. Numbers like 7552 are typically date codes. The cap was manufactured in the 52 week of 1975 which agrees with your comment of 30 years old.

A power amp with unregulated supplies, lets say something like 50W/ch, will idle with about +/- 40 V on the power supply. If you load it with a dummy load and drive it to clipping on a bench, the supply will sag typically to about +/- 30V for this type of amp and more 60/50 Hz ripple will be present.
Now remember that power = V^2/R so if the supply stayed at +/-40 it would be able to deliver much more power, and indeed this is where the dynamic headroom comes from. The supply does not sag much during short peaks in the music and the amp can deliver more power during these peaks. Where there are more repetitive peaks of longer duration the supply sags, bigger caps provide a longer time constant so that more repetitive peaks can be handled without clipping and there will be less 60/50 Hz ripple. It really does make a difference and even many years ago Dynaco sold an add on capacitor box for the ST400, I think it was 100,000 uF.
It is always interesting to think of things at the limit, if we think about infinite caps the supply would never sag and then the RMS continuous rating of the amp then becomes equal to the dynamic headroom value, it would also have no ripple. This is similar to a regulated supply.

Here are some quick calculations for a typical 50W example, assuming that the output stage comes within 2 Volts of the rails and does not current limit:

Hmm, this table gets ruined by the forum software, moderators can I inline HTML here or how is it done?

Idle, Full power 8 ohm, Full Power 4 ohm
V+/- , 40 V, 30 V, 27
Vpeak out , 38, 28, 25 = V+/- - 2
Vrms out, 26.9, 19.8, 17.7 = Vpeak out *.707
8 ohm power, 90 W, 49 W, N/A = Vrms out^2/8
4 ohm power, 180 W, N/A, 78 W =Vrms out^2/4

You ask good questions Beppe.

Pete B.

Dear Sirs,

I have bought a 30 years old integrated amp.
How can I assess if the capacitors (originals) must be replaced?
Aestetichally they appear in good shape.
There is no form of leakage or other.
They are SPRAGUE 36DX and rated 7200 uF /50 VDC.
There is also a serial number 7552.C.

Thank you so much.

Kind regards,

beppe61

 

[PB2]

Let me add:

The power at idle is what the amp will put out for short peaks without clipping and so we can compute the dynamic headroom:
8 ohm dynamic headroom = 10 log (90/49) = 2.64 dB
4 ohm dynamic headroom = 10 log (180/78) = 3.6 dB

Also note that with infinite caps the RMS continuous output would be 90W into 8 ohms and 180 W into 4 ohms. You can see what happens as you make the caps bigger.
Increasing the caps by 4X usually makes a significant difference, but as others have said you have to watch inrush current on the bridge and power switch.

A transformer on the small side (cheap) with higher internal resistance will naturally limit inrush current.

Pete B.

 

[jacco vermeulen]

If I seem too much enthusiastic about this simple "operation" just think this is my very first time !

Beppe,
there are plenty of people on this forum who recognise this from memory.
Replacing 30 year old capacitors that must have dried out considerably by new ones, which are bigger and faster, should make quite a difference.
Going for Rifa's instead of Sikorels was a good choice, remember that construction of Rifa's is unlike other capacitors. Rifa capacitors contain a liquid, and have to be placed standing upright because of the pressure relieve valve on the top.

 

[beppe61]

Re: Re: How can I understand if it is time to replace capacitors?

Dear Pete,

thank you greatly for your extremely kind and valuable reply.


>

Hi beppe61 hope things are good with you,
I'm a bit late here but I wanted to mention a few things. Numbers like 7552 are typically date codes. The cap was manufactured in the 52 week of 1975 which agrees with your comment of 30 years old.

Thank you very much. Very very interesting knowing about the production date.
What can you tell me about the shelf life for NOS caps?
I read is quite long.
The old caps do not leak but with them installed the sound was less strong, less definite.

> A power amp with unregulated supplies, lets say something like 50W/ch, will idle with about +/- 40 V on the power supply. If you load it with a dummy load and drive it to clipping on a bench, the supply will sag typically to about +/- 30V for this type of amp and more 60/50 Hz ripple will be present.
Now remember that power = V^2/R so if the supply stayed at +/-40 it would be able to deliver much more power, and indeed this is where the dynamic headroom comes from.
The supply does not sag much during short peaks in the music and the amp can deliver more power during these peaks.
Where there are more repetitive peaks of longer duration the supply sags, bigger caps provide a longer time constant so that more repetitive peaks can be handled without clipping and there will be less 60/50 Hz ripple.

You have given me a lecture on caps ! very very good indeed.
Now I have something to study very deeply.
I must tell you that these things (caps) are intriguing me very much. They are power reservoirs in the end.

> It really does make a difference and even many years ago Dynaco sold an add on capacitor box for the ST400, I think it was 100,000 uF.

WOWW !!!! 100.000uF is an awful lot. Are they really needed?
What kind of amp (power rating) this Dynaco was?
was the caps box connected by an umbilical extension cable?
how long this cable can be at maximum? this option is very very interesting to me indeed. I am thinking about it.

> It is always interesting to think of things at the limit, if we think about infinite caps the supply would never sag and then the RMS continuous rating of the amp then becomes equal to the dynamic headroom value, it would also have no ripple.
This is similar to a regulated supply.

I understand this quite clearly.

> Here are some quick calculations for a typical 50W example, assuming that the output stage comes within 2 Volts of the rails and does not current limit:

Hmm, this table gets ruined by the forum software, moderators can I inline HTML here or how is it done?

Idle, Full power 8 ohm, Full Power 4 ohm
V+/- , 40 V, 30 V, 27
Vpeak out , 38, 28, 25 = V+/- - 2
Vrms out, 26.9, 19.8, 17.7 = Vpeak out *.707
8 ohm power, 90 W, 49 W, N/A = Vrms out^2/8
4 ohm power, 180 W, N/A, 78 W =Vrms out^2/4

Thank you so much for this extremely interesting calculations.

> You ask good questions Beppe.
Pete B.

I strongly wanted to try to understand something on the topic of PS for audio amp.
Now I have to wait at least two week for some burn-in effects.
I promis to report again after that.

Dear Pete,
thank you so much for your extremely kind, friendly and valuable advice.

I wish you all the best,

beppe61
Italy

 

[beppe61]

Beppe, there are plenty of people on this forum who recognise this from memory.

Dear Jacco,

thank you very much for your extremely kidn and valuable reply.
I have to tell you that at school I preferred labs rather than books.
I am an experimental kind of guy.
Unfortunately I am not so good at theory that I think it is always the base of knowledge.

> Replacing 30 year old capacitors that must have dried out considerably by new ones, which are bigger and faster, should make quite a difference.

One thing I have understood, Not all caps are equal in performance.
The speed in charging and discharging I understand is critical for a dynamic sound.

> Going for Rifa's instead of Sikorels was a good choice,

tha Sikorel are in a box waiting to be used.
I read great things about them.
But due to their dimensions I have to pull out the transfromer from the chassis to make space for them.
Maybe in the future. Now I want to assess the quality of these Rifa.

> remember that construction of Rifa's is unlike other capacitors. Rifa capacitors contain a liquid, and have to be placed standing upright because of the pressure relieve valve on the top.

THANK YOU VERY MUCH FOR THIS VERY IMPORTANT NOTICE.
So I have to put my amp upwards because the screws are in the lower part of the chassis (or rewire everything. A possibility).
On the basis of the first listenings I am quite optimistic about the result. Really.

I will let you know.

Thank you so much again.
Kind regards,

beppe61

 

[beppe61]

Dear Friends,

just an update after having installed 2 new 10.000uF/63V Rifa PEH 200 in my amp.
These caps are really good.
I can safely say that:
1) the bass has gained definition and power
2) the transparency has increased evidently
3) the noise has lowered (I can hear more things, if you know what I mean).
A nice improvement over my 30 years old Sprague caps.
A side note.
I understand that the high-end brand Gamut uses white Rifa caps in its power amps.
I heard that the Gamut sound is very remarkable indeed.
Food for thought.
To end, I think that these Rifa caps can be safely recommended for high quality power amps PS.

Thank you everyone for your extremely kind, friendly and valuable advice.

Kind regards,

beppe61

 

[peranders]

Beppe, a friendly hint: Avoid quoting, do it only when the reader might wonder which post you are referring to and if you really do qoute, take only the interesting part of the text. Much easier to read you see.

 

[beppe61]

Dear Mr. Peranders,

thank you so much for your extremely kind and friendly advice.
The problem is that I get replies with 3 or 4 statements different for content and I would like to reply to each statement separately.
And I have not yet worked out how to do it.
May be I can quote just the beginning of the sentence ?
I understand perfectly well your point, anyway, I am sorry for this.
Besides as I understand that you are from Sweden and Rifa is a Swedish company, what do you think of their caps?
What is you brand of choice when speaking of filter caps for power supply (I mean those big ones for power amps).

Thank you very much indeed.
Kind regards,

beppe61