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Why 12 power transistors in a class AB (?)120 W (?) amplifier?

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DanielT

DanielT

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Failing supply caps will add hum and buzzing in the output typically seen at 120 Hz and harmonics from a bridge rectifier. If you are already in there, replacing the bulk electrolytic caps is probably easy and fairly cheap insurance. Use a good name brand.

FWIWFM - Don
Thanks Don for the tip. Well, if I have to do one thing, I can do the other one too :)

Here a small amplifier is tested. 4700 extra uF is added and it is measured if there is any difference. I find it interesting. It obviously got better. Mainly in the lower frequency regions.

11:00 in he shows how he did. Then various measurement results which he shows with his oscilloscope.


Edit:
Damn there seems to be something wrong with the link. I have to press it once more to get it started. . Do not know if it is the same with you? There is probably a Youtube crap rule that prevents publication.
 
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sarumbear

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solderdude

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The on-off switch will spark inside.
The inductance of the transformer and capacitance connected to it on the primary side may resonate at a certain (high) frequency
Max. current will be very short lived which most rectifiers will survive.

When this weren't the case all electronic devices would have serious problems. Doubling the capacitance won't change much.
 

tomtoo

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The on-off switch will spark inside.
The inductance of the transformer and capacitance connected to it on the primary side may resonate at a certain (high) frequency
Max. current will be very short lived which most rectifiers will survive.

When this weren't the case all electronic devices would have serious problems. Doubling the capacitance won't change much.

Yes but that makes the explaination of @sarumbear not better.
 
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DanielT

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It will be ... superduper ... he he ...;)

"Trying hard to look like Gary Cooper (super-duper)"

6800 uF ...


..My friend Björn has stuff going on...:)

..It does not get more fun than you do it.:)
(small cheap pleasures in everyday life)

Edit:
Some powerful class d sub amp that takes care of the lowest frequencies together with Selan who takes care of the rest so this can probably be yummy.:)
 

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pseudoid

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It certainly can't hurt unless you solder the wires the wrong way around.
Now that the dust settled, I think those damn leaking caps get all the toottin' attention; which almost always does not give a good shake to another maintenance tip all DIY PC builders don't argue about.
Check and then properly replace any thermal pads/goo that are between power transistors affixed to heatsinks.
 

Doodski

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Now that the dust settled, I think those damn leaking caps get all the toottin' attention; which almost always does not give a good shake to another maintenance tip all DIY PC builders don't argue about.
Check and then properly replace any thermal pads/goo that are between power transistors affixed to heatsinks.
That's a very good suggestion and brings me to a question. What is the service life of thermal paste? I buy the Arctic Cooling MX-4 that has a rated service life of 8 years and I attempted getting details on the service life of other thermal pastes and there was no info at the time. Anybody know what can be expected from the average thermal paste? I also know that in a certain 100% class A amp I have experience with that they advised to not use regular thermal paste as it does not conduct heat well enough and apparently the amp will not operate properly without high quality paste and again no mention of life expectancy.
 
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DanielT

DanielT

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Now that the dust settled, I think those damn leaking caps get all the toottin' attention; which almost always does not give a good shake to another maintenance tip all DIY PC builders don't argue about.
Check and then properly replace any thermal pads/goo that are between power transistors affixed to heatsinks.
That will be good. Björn, my friend fixes with Selan with some stuff he had at home. :p
I will then help him in a slightly different way after that (with my trailer, driving shit to the recycling station). He will examine the Sela: Regular service, and general check. If there is something wrong with it, he will find it.

Also, please note, I have added various amplifiers to the thread. Here's Selan, the one about transistors and pasta.

IMG_20211024_143805.jpg


Edit:
What about pasta? It looks more like it is, .... hm, I do not know. I'm not an EE.:)

Aha there is no pasta?!?! Or?
 
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ZolaIII

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That's a very good suggestion and brings me to a question. What is the service life of thermal paste? I buy the Arctic Cooling MX-4 that has a rated service life of 8 years and I attempted getting details on the service life of other thermal pastes and there was no info at the time. Anybody know what can be expected from the average thermal paste? I also know that in a certain 100% class A amp I have experience with that they advised to not use regular thermal paste as it does not conduct heat well enough and apparently the amp will not operate properly without high quality paste and again no mention of life expectancy.
It depends on the compounds and oils used. Artic had a slip recently with MX-5.
Some compounds are not suitable for some applications (depending on disposition surface and that it can damage it) like liquid metal.
You will find life time declaration only on some and more premium products only.
 

Doodski

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It depends on the compounds and oils used. Artic had a slip recently with MX-5.
Some compounds are not suitable for some applications (depending on disposition surface and that it can damage it) like liquid metal.
You will find life time declaration only on some and more premium products only.
Thanks for the heads up about MX-5. I almost bought MX-5 a week ago for my new PC build and I wanted the more easily spreadable MX-4 and so I bought MX-4. The performance of the two are near identical.
 

ZolaIII

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Thanks for the heads up about MX-5. I almost bought MX-5 a week ago for my new PC build and I wanted the more easily spreadable MX-4 and so I bought MX-4. The performance of the two are near identical.
MX-5 is currently most widely used thermal paste (partly because hype, partly because it really performs good and mostly because its widely available for a good price). MX-4 never had such popularity and performs a little worse (not that it's bad in any regard). Artic got famous with it's Silver 5 back in the days.
yqSq6qVDxvcsSQc3kFUvfG.png
Graph is more as reference. Take a look at new Noctua NT-H1 and MX-5 are on about same lv.
 
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Mnyb

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I have seen marginal voltage used in some power supply capacitors.

Is this amp old enough to be made before the EU standard of 230/400 volt Sweden was a 220/380 volt country before that is the amp marked as 220 volt or 230 volt ? Variation +-10 % is allowed. So network can be 253 volt nowadays if your unlucky.

So the advice to stick to original voltage rating or higher is good one

So a quick check with a multimeter what is the unloaded DC voltage ( amp idling not playing music ) ? At what network voltage ? For good measure just add 10% chose a voltage rating that is higher with some margin .

If you can see the rating on the transformer you can calculate the rectified DC voltage.

Note ! If our unfamiliar with the proper use and precautions to do such a measurement just don’t and let your electrician or electronics educated friend do it .
 

Mnyb

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Oh and don’t deviate to much from the original design in any kind of repair work . ( including components specs )

Things are the way they are for a reason , I would not trust myself to do that.

This is a case where a little knowledge becomes dangerous .

You may think you have better idea than original designer but you don’t :) they may very well have accounted for parasitic properties of the components when designing the circuit or other peculiarities a component can have.
So just throwing in “better” stuff might not yield the results you expect .

There are to many tweaks around the net either doing nothing or making things worse
 

pseudoid

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PSA:

Kona scams - Best to avoid those that are labeled Kona "Blends"; unless you like to take a trip to oxymoronia!
And if Kona "peaberries" get your attention, make sure that your wallet can handle a $50 hit for just an 8 ounce package.
KickAss used to sell it decades ago, when they were based out of Hawaii and before demand became the exclusivity of the rich-set!.
Caveat Emptor!
 

restorer-john

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MX-5 is currently most widely used thermal paste (partly because hype, partly because it really performs good and mostly because its widely available for a good price).

Dow Corning 340. Don't mess around with anything else.

1643675822214.png
 

Doodski

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Dow Corning 340. Don't mess around with anything else.

View attachment 183462
Dang they use a different thermal conductivity spec than the majority uses and that makes it tricky. The stuff sure is expensive.

EDIT: Come to think about it the quantity of Arctic Cooling MX4 that I get for $10 is miniscule and so 5oz of DC 340 for $40 is not so bad I suppose.
 

pseudoid

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Dow Corning 340. Don't mess around with anything else.
Ummmm...
ASTM is a thing: Dow340 surpasses ASTM.
But this does not mean that technology stands still!
I have utmost 'trust' in Noctua brand; lemme cite a few relevant specs, if I may w/o slicing dBs or bits.
Noctua #NT-H1:
"Specific Gravity": 2.4g/cm(cubed)
Edit for emphasis:
"Recommended Storage Time": <2years
"Recommended Usage Time": <3years
End Edit

"Peak Operating Temp": +110C
"Recommended Operating Temp": +90C
I keep a bit around for my overclocked CPUs and have nothing but success with their products and this does NOT mean competitors have been standing still, as competition is fierce for gamers rigs.
Reformulated Noctua #NT-H2 needs to replace my older spare syringe.
 
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restorer-john

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Dang they use a different thermal conductivity spec than the majority uses and that makes it tricky. The stuff sure is expensive.

EDIT: Come to think about it the quantity of Arctic Cooling MX4 that I get for $10 is miniscule and so 5oz of DC 340 for $40 is not so bad I suppose.

Dow 340 is used by aircraft manufacturers for avionics, the US military, Suppliers to NASA etc. Seriously relaible, life depending on it type stuff- not a gaming pooder in a basement.
 
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