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

Doodski

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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.
Hmmz. The thermal conductivity of the two are very different and the shelf life is very different too. 8 years for MX-4 versus 5 years for DC340. Is Dowsil340 the stuff you recommend? Or is this a similar named product?
thermal 1.png


thermal 2.png
 

restorer-john

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Shelf life and opeational life are completely different.

Silcone heat transfer compounds break down on the shelf and the oil separates from the fillers. The oil is the carrier and dries up in use, leaving the transfer compound oxides.

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Several years back, my partner's son had a $5800 Dragon edition MSI super gaming laptop pooder (3xSSDs and 32gB ram i7 etc etc) that overheated from new and once I'd removed all the stupidly thick 'thermal compound pads' from the heatsinks and correctly applied 340, the machine ran cool and quiet. It used to sound like a turbine with two giant fans on the bottom going flat out. I still have that machine and the fans never run up fast anymore.

No PCs or pooders I have worked on in this house have anything other than 340 on the heatsink-devices. Video cards get 340 at the time of their first fan/heatsink clean out. I've been using it on pooders since CPUs started to need fans!

By all means, get a tube and compare temperatures on the CPU die for the same workload and report back.

Check out the attachment PDF
 

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DanielT

DanielT

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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 .
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
I do not know how old it is, from the early 1980s maybe.

Changing electrolytic capacitors was mostly by chance now that Björn had stuff at home. It is not certain that it is needed. How large the electrolytes can be, without, for example, the rectifier bridge being damaged is something that is addressed in the the thread a few pages back. It will be a little more uF now, but not too much.So the "turbo pressure" is not turned on too much. It should be able to handle the slightly larger vessel.:)

Björn, my friend, will check that it is ok, with the instruments he has. Do not know what he has for measuring stuff, but 100% security a miultimiter in any case.:)

Of course it's a gamble. But what would life be without a little gamble?:D
 

ZolaIII

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@restorer-john I already had that paper. MX-4 actually cost the same (45g pack).
Anyway if you ever need a fan take a look at their P-CO (pressure optimised constant operating) lineup.
Edit: did a research. The DC-340 is actually most similar to old Artic Silver 5 (chemical [silicone base] and performance wise, actually Silver whose a tad better) and I wouldn't recommend it (as it's electric conducting) even performance is satisfactory. The MX-4 is a good performer and probably best one for the price. The MX-5 and Noctua NT-H1 are little better but not really worth 2x the price (which will probably go down in time) and if the price is not a problem and you really need the performance it offers (-1.5~2°C compared to good one) there is no better conventional one currently than Grizzly Kyronaut. Those are all naturally not electrical conducting one's. The liquid metal is not suitable for most applications anyway.
 
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DanielT

DanielT

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A little more information about this power amp. Its power I guessed seems to be correct::)

"Sitting and idly reading various posts and then fell into the thread about the power amp ea232 from SELA. At the time when it happened, I was working extra as a cinema operator. In 1978, the sound system at the Royal Cinema in Gävle was modernized, which then received the then new "Dolby Stereo", which was an optical two-channel soundtrack from which four channels were extracted. the output stage that was installed was precisely the ea232. They gave 2x125Watt. These were in daily operation for eleven years without a problem.
Attaches a picture of the sound rack (engine room)."

Royal maskinrum och foajé.jpg


 
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