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Exposure of fake Chinese tube amplifier Nobsound MS-10D MKII.

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Exposure of a fake Chinese tube amplifier Nobsound MS-10D MKII.  What do professionals think?

 

 

I disassembled a Nobsound MS-10D MKII and found it was an imitation of a tube amp. An empty box was attached on the top of the amp, that pretends to look like a real tube amp. In the box suppose to be three transformers. One is for power and two for each channel for matching tubes with speakers. 
There is only one power transformer under the box, which delivers 17V to output transistors, 7V to microchips and 6.8V to tubes. As we see there is not the high voltage for the tubes. The transformer is not high-quality, noisy. I had to repair it. 
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The Amplifier without tubes or without at least one tube does not work.
I applied the variable signal 2B to the input of the amplifier and looked where it comes to  when the 6n1p and 6p15p lamps were removed. The signal goes to the grid 6n1p tube only!  I put the tubes back and then I found exactly the same signal after tubes got warm up on the grid and the cathode of the 6n1p tube and on the anode and cathode of the 6p15p tube. Where from the signal comes on the 6p15p tube it is not clear. 20180503_155724.jpg.b923f41ec2ff80bfba5797ce3ff588d4.jpg
 
It is clear that the signal is not amplified in the tubes, but somehow participates in the work. A circuit diagram is very difficult to draw, because the circuit is on both sides of the board and the details are too small. The preamplifier is made of a chip JRC4558. 

I think  the tubes form a delay time either opening or closing a transistor or chip. I'm sure that the amplifier will work with any other tubes having same pin arrangement.
Owners of the amp argue on the forums which Chinese or Russian tubes sound better. There was reported that Russian tubes sound much better, and the tubes with golden grids make the best sound. I think they are a self-hypnosis. Unfortunately, I do not have other lamps to judge the disputants. 

 

Question to the experts. 
What function do tubes perform? 
Where does the signal on the cathode 6n1p and on the cathode and anode 6p15p comes from, if the signal comes on the 6n1p grid only when tubes are removed?

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Yeah, I read the post. I'm still laughing at the claim that some listeners reckon they can hear a difference between different valves.

 Best laugh of the day. So far. 

 

Still, it's early.

Edited by Zaphod Beeblebrox

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Priceless... or should that be worthless.

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Moderator

its got a dial uv meter on the front ! :)

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Unreal, the Chinese have a reputation well earned.

 

 

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39 minutes ago, lusk said:

 

Unreal, the Chinese have a reputation well earned.

 

 

Those of us at the coal-face (techs, engineers, etc) have a very healthy disrespect for Chinese made products. It all started with those counterfeit semiconductors which appeared at around the same time as Chinese made valves (around 25 years ago). Although the valves have improved, the Chinese counterfeit semiconductors are still being produced. I was caught a few times. Now I only source semiconductors from ISO accredited sources. I've certainly worked on a few Chinese audio products. Some are pretty decent. Some are not.

Edited by Zaphod Beeblebrox

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Their Electrolytic caps were pretty crap too.

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