To Siemens Sikorel caps users - a kind question

[beppe61]

Dear Sir,


I have some kind questions for people who have experience of Siemens Sikorel caps in power amps power supply.
I bought some New Old Stock (1993) 15.000uF/100V Siemens Sikorel caps.
Can they be still used with good results or are they "expired" (this is the very important question. They are 12 years old actually but I have been told never used)?
What sort of changes should I notice during the break-in period?
For now they have decreased the noise and increased transparency.
The bass is not fully resolved anyway. Not deep enough I mean.
To sum it up, the sound is good, bass (<100 Hz) apart.

I woudl appreciate any kind advice.
Thank you very much indeed.

Kind regards,

beppe61

[MRupp]

Beppe,

The Epcos (formerly Siemens) Sikorel datasheets state a "useful shelf life" of 10 years and I would think there is a safety margin, so even after 12 years they should still be fine. If you want to be on the safe side - and have the time, off course - you could reformat them. In case you don't know how there are posts about reformatting on diyaudio.

Btw, what caps did you use before?

[beppe61]

Dear Mr. Rupp,

thank you so much for your extremely kind and valuable reply.
Let me please explain better my experience.

>

Originally posted by MRupp
Beppe, The Epcos (formerly Siemens) Sikorel datasheets state a "useful shelf life" of 10 years and I would think there is a safety margin, so even after 12 years they should still be fine.

Thank you so much for this very valuable to me info.
Actually they are made in the 1993 (05 and 12 month).
They are labelled Siemens series B41570-A9159-Q.
15.000uF/100 V with a big screw at the base.

> If you want to be on the safe side - and have the time, off course - you could reformat them.
In case you don't know how there are posts about reformatting on diyaudio.
Btw, what caps did you use before?

Dear Mr. Rupp,

I have this 30 years old amp that I am trying to renovate.
The original caps are 2 Sprague (made in 1975) 7200uF/50 V.
Then I bought 2 RIFA PEH200 10.000uF/63 V (compatible for dimensions).
The sound improved in trasparency and power.
Then I found on ebay 8 of these Sikorel and I am using 2 with the amp.
For their dimensions they are temporarily mounted outside the chassis.
From the start they seems fine.
I would like to go on a little with the break-in before pulling-out the transformer to place them inside.

Could you give me any info about the influence and duration of the break-in process?
The sound get better ?
I hope for more bass impact.
I have two current hungry Dynaudio to drive.

Thank you very much indeed again.

Kind regards,

beppe61

[PB2]

See: APPLICATION NOTE
RECONDITIONING ALUMINUM ELECTROLYTIC CAPACITORS:


http://www.duracap.com/electrolytic_...tion_guide.htm

[beppe61]

Originally posted by PB2
See: APPLICATION NOTE
RECONDITIONING ALUMINUM ELECTROLYTIC CAPACITORS:
http://www.duracap.com/electrolytic_...tion_guide.htm

Thank you very much.
I will try to do it.

Kind regards,

beppe61

[PB2]

Hi Beppe,

Just wondering what the PS idle voltage is of your amplifier - the voltage on the power supply caps?

Part of the capacitors insulator is the oxide layer that forms on the plates. This oxide layer decays, or disintegrates over long periods of time with inactivity - typically years. Less insulation means the rated voltage becomes lower and therefore leakage current begins to flow which can be dangerous (heat is generated) when voltage is applied without current limiting. Capacitors have a surge voltage rating and this is why they form the cap to 110% of the rated voltage, through a current limiting resistor. This small current promotes growth or reformation of the oxide layer. The oxide layer keeps growing until the current stops, therefore if we only reform the cap to it's rated voltage it will no longer meet the surge rating of the cap.
Do you have a source for 110V DC?

I just recently pulled out an old amp that I built which has 5000 uF/50V Mallory capacitors and IIRC the date codes were around 1965. This amp has not been powered up in probably 10 or 20 years. I installed current limiting resistors and powered it up, now the PSU only has +/-32V on these caps but one was fine at least at this voltage right on power up taking only a few minutes to charge. The other took about an hour, and I believe that it was reforming. I was just curious to see the state of these caps, I don’t expect to use them. I might try to see if they’ll reform at 110% or 55V just out of curiousity, and I’d probably let them form over night. The point is that these caps are about 40 years old and at least one seems to work at this reduced voltage. However, I would not trust or use them at this point.

Pete B.

[beppe61]

Hello Peter,
how are you? hope fine.
I answer to your questions hereunder.

Originally posted by PB2
Hi Beppe, Just wondering what the PS idle voltage is of your amplifier - the voltage on the power supply caps?

+/- 41.8 exactly on the filter caps terminals.
Perfectly the same on each rail (I mean +41.8V and -41.8V).
But dear Peter, I discover one thing after another.
Yesterday I replace the old bridge made out of discrete diodes with a new monolithic powerful one with a very beneficial outcome !
Less noise, more power in the bass !
I know that my approach is not scientific and rational at all but I
am using this old amp as a workbench.
Better would be to find an amp kit to do all the experiments.
After this I found an article about diodes bridge in power amps that mentioned that also the myth Nelson Pass prefers the integrated solution.
I intend to buy some 400V/25A bridges to use for future various mods.

> Part of the capacitors ....
I just recently pulled out an old amp ...
Pete B.

Dear Pete,
thank you very much for your extremely kind and valuable advice.
You give me material to study for the next 3 months!
The electro caps are indeed misterious things.
On the basis of the info I have gathered here and there they are practically the "only" components subject to aging.
My take is, do not use caps older than 20 years.
I have at disposal some new old stock Sikorel made in 1993.
Their shelf life is said to be 10 years.
In my case it shoudl be 12 years now.
I also read that they do need quite a long break-in period.
I went back to Rifa (new caps) because of practical reasons.
But I tell you that this experience with the new diodes bridge has been quite positive.
Maybe there were also some porblems with contacts.
Now the sound of a piano is more powerful and definite.
As i said my approach is really unscientific but some effects are quite evident after some listening session.
For caps reforming, I would do that directly inside the amp, with the caps placed.
Anyway I would try any cap and after some 100 hours and I would judge by sound (if I like it or not).
In the end I think that what we like is good.
And this could sound as a concession to audiophile people, who judge only by ears.

Thank you very much again for kindly disclosing with us your extremely interesting experience.

Kind regards,

beppe61

[beppe61]

Dear Friends,

on the basis of your personal experince could you suggest me a really good example of monolithic diodes bridge ?
It made a difference in the power supply of my current amp.

Thank you so much indeed.

Kind regards,

beppe61