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Renovating a set of amplifiers and filters from 2 Penta's

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Beobuddy
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On request I've renovated a set of filters and amplifiers from 2 Penta's.

As probably already known, the caps losts there value and sometimes, probably most times they are the cause  of malfunctions.

So here are some pictures.

Each penta has 2 filters, one for the mids and one for the low/high section.

First pictures from both filter inside the bottom.

 


Beobuddy
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Pictures from the filters before and the used components.

 


Beobuddy
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Pictures after replacing the caps and resistors.

Now we have two identical filters.

Underneath two boards are some "hidden"caps.

Some small modification is needed on the bottom cover of the penta. 

 

 


Beobuddy
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Look at the difference between two capacitors.

 


Beobuddy
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The amplifiers are also done. All the caps inside and some ic's are changed by better versions.

Takes  lots of labour, but it is very noticable. The way the penta now sound, is a huge difference! Like a curtain is taken away in front of the speaker!

 

 

Leslie
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Leslie replied on Thu, Mar 1 2012 10:59 PM

Great pictures taken Beobuddy! Can you give us an estimation about the costs for recapping those 4 filterboards? I think I can do this job myself!

Brengen & Ophalen

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Leslie replied on Thu, Mar 1 2012 11:00 PM

Btw, are these Penta 2 boards?

Brengen & Ophalen

Step1
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Step1 replied on Fri, Mar 2 2012 8:14 AM

no doubt silly silly money for those caps! If you do this sort of thing on a regular basis it is worth investing in a good quality ESR meter before blindly spending a lot of money and expecting worthwhile results IMO!

Olly

chartz
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chartz replied on Fri, Mar 2 2012 9:44 AM

Beobuddy:

a huge difference! Like a curtain is taken away in front of the speaker!

No doubt the improvement will fade away with time. But then if you're happy, so be it! Are you keeping the original cables?

Great pics!

 

Jacques

Beobuddy
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Leslie Nelwan:

Btw, are these Penta 2 boards?

These are mk3, first serie. (Almost the) Same as the mk2's.  

Beobuddy
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Step1:

no doubt silly silly money for those caps!

Imho, far less silly then the statement made. Probably based on assumption rather then experience and measurements Wink

Beobuddy
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chartz:

No doubt the improvement will fade away with time. 

Despite the diffrerence in quality between the new used parts and the original ones, if ithey last another 15 years, then that's fine with me.

BTW, thanks for the compliment! Just to get an idea.

 

Step1
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Step1 replied on Fri, Mar 2 2012 8:18 PM

I would be very interested in the measurements you have taken that prove my statement so blatantly silly!

 

Beobuddy:

Step1:

no doubt silly silly money for those caps!

 

 

Imho, far less silly then the statement made. Probably based on assumption rather then experience and measurements Wink

 

Olly

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Leslie replied on Fri, Mar 2 2012 11:05 PM

Beobuddy:

Step1:

no doubt silly silly money for those caps!

 

 

Imho, far less silly then the statement made. Probably based on assumption rather then experience and measurements Wink

Well said BeobuddyBig Smile

Brengen & Ophalen

leosgonewild
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Very intrested in price and where to buy parts. 

Søren Mexico
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Step1:

no doubt silly silly money for those caps! If you do this sort of thing on a regular basis it is worth investing in a good quality ESR meter before blindly spending a lot of money and expecting worthwhile results IMO!

I dont agree with silly money, but did you check the difference with an ESR meter, and  what was the total price for the caps.

BTW nice job.

 

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Leslie
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Leslie replied on Tue, Mar 6 2012 11:39 PM

Anyone who can explain what ESR is? I would like to know the price for those caps as well and if there are any other cheaper alternatives. Must be that anything is better then the old originals now, is it?

Brengen & Ophalen

Søren Mexico
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Leslie:

Anyone who can explain what ESR is? I would like to know the price for those caps as well and if there are any other cheaper alternatives. Must be that anything is better then the old originals now, is it?

ESR meter here I'm not sure about the "old" originals, they are not that old, the sound with new audio caps may be better or different, but why change a cap if it reads OK

 

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Leslie
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Leslie replied on Tue, Mar 6 2012 11:52 PM

Thanks Soren! How come you know so much about electronics? By the way, a 5000 Beomaster for sale on Ebay.com....

Brengen & Ophalen

Søren Mexico
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Leslie:

Thanks Soren! How come you know so much about electronics? By the way, a 5000 Beomaster for sale on Ebay.com....

I know Leslie, but from Poland ???. I dont know too much about electronics, but once in while I read about it, generally when I see something I dont know about, I start with the wiki and go from there.

 

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Leslie
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Leslie replied on Wed, Mar 7 2012 12:03 AM

Not from Poland, check here

Brengen & Ophalen

Søren Mexico
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Leslie:

Not from Poland, check here

Warum zum teufel komt so einer auf Ebay Germany wen er nur nach USA versenden moechte, I ch suche Weltwide und nur die Polen dinger komt auf, dass verstehe ich nichtBeer

 

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Søren Mexico
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Sorry for the German got exited did you understand it ??

Collecting Vintage B&O is not a hobby, its a lifestyle.

Step1
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Step1 replied on Wed, Mar 7 2012 12:58 AM

Leslie:

Beobuddy:

Step1:

no doubt silly silly money for those caps!

 

 

Imho, far less silly then the statement made. Probably based on assumption rather then experience and measurements Wink

Well said BeobuddyBig Smile

 

 

I didn't mean this as a personal attack, but I do feel I need to defend my position here! As far as I can see, any 'gains' made with exotic components almost certainly can't be measured, and I suspect will show no difference in a double blind test.... And this is the issue, we often have no tangible evidence as to whether there is any improvement or not, only anecdote! There is plenty of evidence to suggest we can hear improvements that don't actually exist though and I recently fell for such an example when experimenting at home! Basically, we tried a mat on a Beogram 4000. We all screamed "wow, amazing!!" the first time we cued the record. When I say all, there were three of us, myself, a friend and my partner (whom is not into audio quality). Trouble is, we couldn't recreate this wow effect in a blind test lol! So you see, how can we be objective with such experiments that are not conducted under controlled conditions?

Besides, many speaker capacitors I test with my meter are possibly a bit out capacitance wise (but generally within tolerance) but they do show good to very good ESR readings!

Above a 6.8uf capacitor from my S-120's. Within 10% of original value and specs request 20%. Now from what I read on these and other forums this should not really be possible! On a side note I kept these capacitors because after recapping my S120's, there was no difference in sound when comparing between recapped and non recapped :( I didn't have an ESR meter then but planned on getting one, hence I still have a draw full of caps from all sorts of restoration projects!

Also, I am not saying there is no such issue with old electrolytics! I am sure there are plenty of occasions where the capacitors are tired and retard the signal to perceivable levels, but it shouldn't be assumed they are all faulty relative to age!

Anyway, to counter argue my argument above, I would like a meter that is able to test capacitors at lower frequencies, but I don't think there would be a significant difference, and I doubt it would weed out any capacitors that otherwise passed the normal test!

Now I feel like the enemy saying all this - but lets be honest folks what is a forum about if we can't say something that goes a bit against the grain from time to time? We are all here to learn from each other and enjoy our hifi after all!

 

 

Olly

Beobuddy
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Sorry for the late response.

 

@ Leslie and others, the set showed on the pictures, approximately 170 euro.

 

Step1:

 As far as I can see, any 'gains' made with exotic components almost certainly can't be measured, and I suspect will show no difference in a double blind test....

So, and that;s it?

Sorry, but i think ( and I'm really a normal bloke who doesn't believe in special cables from several hundred euro's etc) there is difference between using better components and just spending a lot of money and thinking that the results are improved. 

As I already mentioned. You've probably have no experience with the caps I'm using.

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Another picture.

 


Beobuddy
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The above showed caps have the same value as you can see.

The 2 on the left are used by B&O. I'm a bit shocked as I first thought that the blue one was only used as a replacement cap for repaired boards/penta's.

But recently I did another set of boards and all the caps are like the small blue one!  

Beobuddy
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To continue.

So, with the measured values there would be no difference.

The caps used should have in theory 68 uF and a 0,00 ohm ESR.

The values I measured are (from the left to the right ),

73,50uF (ESR 0,03ohm), 70,86uF (ESR 0,02) and 67,29uF (ESR 0,02 ohm).

 

So, from the perspective about measuring you're right. They have almost the same value, no spectacular differences measured.

But still I dare to state that there is a huge audible difference between them.

Things to argue are, the way the ESR meter measures, the quality of the used components and my experience which are shared or better comfirmed by others.

First thing is the ESR meter. This meter measures with a frequency of 100khz. You probably know that the impedance (not a real impedance I know) can be calculated. Xc=1/WC = 1/ (2*pi*f*C). At a f=100khz, this is way higher than used at a more real frequency, say 10khz.

So, by decreasing the f by 10 times, the Xc increases by the same amount!

If I have some spare time I'm willing to measure the UU/UI based on different frequencies in a test setup to get a more reliable view on how the caps behave. In theorie the ESR should be zero, but in daily practice it isn't.

Second, the quality of the components. I would like to compare the difference in quality as the used tyres on a car.

You can get different tyres with the same dimensions (capacity) and they all can have a maximum speed of 180km/u (max voltage).

But it all comes to how the tyres act in the bends taken. Smaller tyres will give you less grip than wider used tyres.

That's where I think lays the difference and gives you the different audible sound.

 

The last fact I have, is the way I experience since almost 3 years with these caps.

I started at first by making a mono CD with my favourite well known tracks. I mixed them mono with Cool Edit (nowadays Adobe Audition). So I had a source with several tracks where left and right produce the same audio/sound. So I had a good start by setting 2 penta's next to each other. One modified, one not with the older parts.

This gave me a direct A-B comparison, a very noticable one! The second stage was to set them apart and  invite an friend/member of the family over and let them decide if they could here any difference between to 2 penta's. Surprise suprise. Within 2 seconds they all could point at the modified one! This is a blind test. They didn't know before they entered the room.

But at last and not the least, since modifying the penta's I've got almost a dozen penta owners over here, They all, within a snap of your fingers, can hear and can tell you the detail of the difference they hear.

The most people I get are members who are "tired" by the sound of the penta. It sounds dull, doesn't come out of the speakers and are within a few minutes convinced about the improvement.

Those people/members can't be just fouled. No way. That's why it strengthens my positive experience.     

Beobuddy
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Shocking differences.

Front left and right boards are original placed in the mk3's

 


Beobuddy
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About the ESR meter.

This is a nice instrument, which becomes mostly handy for just locating a faulty capacitor.

But just by using an ordinairy ohmmeter, you can do the same. A capacitor should have an unmeasurable resistance used at DC.

Some caps gives you a readable value (several ohms) and sometimes there are even faulty ones which are  internally shortcircuited.

With that in mind, you can change caps in advance without measuring them. Knowing that they will give you one day troubles with leaking/breaking.

The red/orange caps are well proved here on this forum. So, with restoring an object, the first parts removed are the suspicious red/orange and bipolair caps.

Step1
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Step1 replied on Fri, Mar 9 2012 9:44 PM

Hang on you are arguing the ESR of the capacitor measured by the meter is dependent on the test frequency, but then you argue the ideal ESR (I assume at all frequencies) is 0 ohms? You can't have it both ways, I think you are in fact confusing reactive Capacitive with series (non reactive) resistance!

The meter is measuring the effective resistance WITHOUT any reactive content so actually the ESR is largely independent from the test frequency..

When I first got my meter I emailed the company to insure this was the case....

The reply...

Although a capacitor may not offer it's best performance at 100kHz, it's ESR is fairly constant across a very wide range of frequencies as it's predominantly resistive as opposed to reactive. At higher frequencies, the capacitor's inductance, dielectric absorption and other losses can influence the capacitor's characteristics, but these are not directly related to ESR. So this means that ESR is a good indicator of capacitor condition even for capacitors that are not designed for 100kHz.

As an extreme example, a very large reservoir capacitor for a linear power supply may only be designed for ripple currents of 120Hz (typically), but the ESR is still valid at 100kHz (although the capacitor's other characteristics would not be suitable for high frequencies).

So to summarise, as ESR is a resistive effect, it is largely frequency independent and so the readings of ESR at 100kHz are representative of the ESR at the capacitor's application frequency.

By the way, 100kHz was chosen by many capacitor manufacturer's as that allows for a simple impedance test to verify ESR (because the capacitor's reactance is so low at 100kHz and doesn't influence the reading very much). This is not true for small capacitor values (<10uF for example), but the Atlas ESR automatically compensates for the influence of reactance and therefore yields a frequency-independent result.

Regarding the blind test, have you ever tried comparing these capacitors with newly installed, fresh electrolytic bipolars?

Now you are correct in that I have not tried these capacitors, but I have tried many different replacement electrolytics (from the cheapest chinese jobs to audio grade Nichicons etc..) in the signal path of different amps and I have not yet been able to distinguish between different types despite what you read on the internet!

Olly

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Here as an example.

This one fried the resistors (1/4Watt) from the power supply of the analog audio part.

The cap here is (almost) an shortcircuit

Symptom, reads and plays tracks well, but no audio coming through.

 

Therefor all the same type of caps are replaced in advance.

An ESR meter isn't needed here, but stays a handy instrument as you can use it while the cap is still on the board.

 


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Step1 replied on Fri, Mar 9 2012 9:52 PM

Beobuddy:

About the ESR meter.

This is a nice instrument, which becomes mostly handy for just locating a faulty capacitor.

But just by using an ordinairy ohmmeter, you can do the same. A capacitor should have an unmeasurable resistance used at DC.

Some caps gives you a readable value (several ohms) and sometimes there are even faulty ones which are  internally shortcircuited.

With that in mind, you can change caps in advance without measuring them. Knowing that they will give you one day troubles with leaking/breaking.

The red/orange caps are well proved here on this forum. So, with restoring an object, the first parts removed are the suspicious red/orange and bipolair caps.

Using an ordinary meter is not the same as using an ESR meter! Yes a normal meter will weed out a leaky or short circuit cap (as will an ESR meter), and with larger values it could weed out open circuit capacitors, but neither of these bear any relation to the series resistance as seen by the circuit in question, and this is exactly what the ESR meter is designed to do!

Olly

Søren Mexico
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Beobuddy:

About the ESR meter.

This is a nice instrument, which becomes mostly handy for just locating a faulty capacitor.

But just by using an ordinairy ohmmeter, you can do the same. A capacitor should have an unmeasurable resistance used at DC.

Some caps gives you a readable value (several ohms) and sometimes there are even faulty ones which are  internally shortcircuited.

With that in mind, you can change caps in advance without measuring them. Knowing that they will give you one day troubles with leaking/breaking.

The red/orange caps are well proved here on this forum. So, with restoring an object, the first parts removed are the suspicious red/orange and bipolair caps.

In short I will have an ESR meter, and I have a lot of old caps, I will order Audio caps for my 3702s, they have now part new cheap caps and par old ones that read good with an ohm meter. I tend to favor Beobuddy in "bigger is better", but thats only from feeling and no real reason, I've always gone with the measurements, if you cant measure a difference there is no difference, but maybe I will have to change my opinion now.

On the other hand, one has to consider the costs, I payed some US 100 for my 3702s, in good shape and freight included, for Audio caps I will have to pay about 40/50 US pr. speaker.

End of March I will be back with results, have to pick up my items in TX.

 

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Step1
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Step1 replied on Fri, Mar 9 2012 10:05 PM

As I said above Soren using an ohm meter will only catch faults at extreme ends, and even that depends on the value of the capacitor! Same with DC supply or any other standard measurement technique.

ESR meters are great for spot checking the condition of capacitors before deciding whether to replace or not, but they are useless for general troubleshooting!

They do make a very good low ohm meter too!

i generally find the red RDE's and often green tants(?) are the ones to really look out for! I always replace on site!

Olly

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Step1 replied on Fri, Mar 9 2012 10:06 PM

@beobuddy I do like your voltmeter :)

Olly

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Beobuddy replied on Fri, Mar 9 2012 10:13 PM

Step1:

Using an ordinary meter is not the same as using an ESR meter!

I know, but it will do in most cases do the job, just fine. I didn't state that both meters are the same, not at all. 

I'm just having thoughts about the results of a ESR meter using several mA's and the difference of a cap in full working order (several A's)  which could explane the audible difference. 

All the caps are tested ok with the ESR meter, but what happens with them (how do they behave) when a current of several ampere's are going through them. Still leaves me with the audible difference.

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Beobuddy replied on Fri, Mar 9 2012 10:15 PM

Step1:

@beobuddy I do like your voltmeter :)

 

 

Thank You for the compliment! Big Smile

It's a nice voltmeter, just for some analog readable tests. I use mostly the Fluke.

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Beobuddy replied on Fri, Mar 9 2012 10:19 PM

Step1:

i generally find the red RDE's and often green tants(?) are the ones to really look out for! I always replace on site!

Recently I got also cracked orange versions. Cracked from the bottom upwards and just below the top. Like it's going to lift it's top off.

Rick
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Rick replied on Fri, Mar 9 2012 11:02 PM

I have great success with my Huntron's and then an ESR if I suspect something.  I look for a tilted oval indicating a restance problem.  Then pull and check if needed.  Saves the time of pulling and getting a good ESR reading, though this can be done in circuit. It might not give me an exact value but I can check a ton of caps quickly.  Plus I have gotten pretty good at telling a rough value by the freq/voltage I am using and the size/shape of the oval. 

Rick

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