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Another Newbie Who Bought a Cheap Chinese Tube Amp Kit
Another Newbie Who Bought a Cheap Chinese Tube Amp Kit
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Old 28th November 2018, 04:41 PM   #1
Lotus78 is offline Lotus78
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Default Another Newbie Who Bought a Cheap Chinese Tube Amp Kit

I purchased one of those cheap Chinese tube amp kits. I did some due diligence (ie google) but not much came up. So, I figured I would give it a whirl for $140 with free shipping.

I have very little knowledge about circuits and what the various parts do. I learned which end of a soldering iron to hold just a few months ago and managed to put together the crossovers in the Parts Express Overnight Sensations

I purchased this one: 6N1+6P3P Amplifier HiFi Class A Tube Audio Vacuum Power Amp DIY Single Ended Kit | eBay

I was expecting step by step instructions but what I got is one piece of paper with a schematic and some text. In Chinese. Instead of packing it backup and sending it back I made the second mistake of going ahead and trying to build the thing. After all it is only $140. My new mantra.

The endless research done to figure out were to start led me here where I found out

A. I should have never purchased this amp because it does not come with instructions.
B. It is a poorly designed amp.

I assembled everything easily, did a quick tutorial on reading schematic and researched output transformers. The output transformers seemed easy enough so researched power transformers a little more daunting but in the end not too bad.

But, to me those where the easy parts. Everything in between looks much more difficult and the chances of me not making a mistake somewhere is slim to none. That is if I not already have not made a mistake. So, after all my long windedness. My question is what should I do next? (It is a multiple-choice question)

A. Stop wasting my time throw the whole thing away and keep telling my self it was only $140
B. Finish it, plug it in, turn it on and take out the power grid for miles then throw it away and tell myself it was only $140
C. Finish it take it to a tech before I plug it in let him/her look over it. Thus, this project will now be over $200+ for a poorly designed amp.
D. Stop now take it to a tech and let them finish it. Making this a $300+ poorly designed amp
E. None of the above.
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Old 28th November 2018, 05:16 PM   #2
Lingwendil is offline Lingwendil  United States
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If I'm not mistaken Wavebourne picked up one of these a while back, hopefully he chimes in soon. He built it up as a testbed for something else though. Here's a build based on one, has a schematic shown too- Tube amplifier kit from ebay

It has a few underside shots too, if that helps. How far have you gotten in the build? If you post up some pictures of the current state of things folks will be happy to help as best they can.
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Old 28th November 2018, 06:09 PM   #3
Eli Duttman is offline Eli Duttman  United States
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That schematic Lingwendil linked is interesting. It says 6P3P or EL34. However, the 6P3P datasheet seems to suggest that the type is electrically closer to a 6BQ5/EL84 than it is to an EL34. I don't read Hanji and could easily be misinterpreting things. That 5.4 W. is what caught my eye.

That's not a terribly bad design and can (within the limits of the provided magnetics) be made into a pretty good design. IMO, the fact that it's a point to point (P2P) setup, not a printed circuit board (PCB), works to our collective advantage.

The 5Z4P rectifier is, basically, a 5Y3 with a cathode sleeve.

If the OP is interested, I can provide a few ideas about squeezing every last drop out of the magnetics.
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File Type: jpg Chinese Amp Schematic.jpg (40.8 KB, 1348 views)
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Old 28th November 2018, 07:15 PM   #4
Alllensoncanon is offline Alllensoncanon  United States
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Another Newbie Who Bought a Cheap Chinese Tube Amp Kit
Think of it like this, You are buying a pair of output transformers for $60, a power trans for $20, a choke for $10, 4 octal sockets for $10, a preamp and a rectifier tubes for $5 each plus a chassis (no paint) for $10 and the shipping cost is $18. The rest of the stuff are free. It is not a bad deal unless you already have plan to spend 2X more money.



I would also suggest using the schematic in post #2.
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Old 28th November 2018, 10:54 PM   #5
H713 is offline H713  United States
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Option F:
Buy Morgan Jones book on building tube amplifiers. As mentioned before the limiting factor is the magnetics, but even still one can put together a pretty decent amp with those parts.

The people here will be a huge resource, as is the book I mentioned above. Also, there are a few YouTube channels with very good video series on this subject. Blueglow Electronics and Xraytonyb both have series that are geared towards someone building their first amp.
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Old 28th November 2018, 11:26 PM   #6
Lotus78 is offline Lotus78
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Thanks all. But Iím a stone-cold beginner and need an entire schematic to slowly digest. I do have wavebourneís schematic and picture down loaded from my original research I will look at it. I have watched several hours of those Blueglow videos. Very helpful and got me started. I will check out Xraytonyb and the book. A win for me right now is something that will make sound not smoke in the end.
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Old 28th November 2018, 11:36 PM   #7
Eli Duttman is offline Eli Duttman  United States
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Quote:
I would also suggest using the schematic in post #2.
I "lifted" that schematic and brought it here.
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Old 29th November 2018, 12:10 AM   #8
avtech23 is offline avtech23  Australia
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Another Newbie Who Bought a Cheap Chinese Tube Amp Kit
I'd keep going if it were me. You have all the parts necessary and there are plenty of resources available here to help you get through the build.

It doesn't necessarily matter that the design might not be the best - it was $140 after all - but when it is up and running you'll get the sweet satisfaction of bringing an amp to life. Think of the $140 as a learning opportunity.

The schematic is the roadmap. All you need to do is be methodical when wiring and have a read of some of the 'tube amp wiring guides' available on the internet and you'll be alright!
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Old 29th November 2018, 12:31 AM   #9
Lotus78 is offline Lotus78
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I was researching just what the 6n1 tube was for. I guess Allensoncanon answered that. Basically, this is not a power amp with a volume but an integrated amp. I have a preamp in the same case as this amp that I was going to use with it but if Iím going to use only one source I guess there in no need. The wife asked me what I was going to use this amp for and I told her I donít know. She has been inching to build a pair of single driver folded speakers and likes the look of this amp for the living room. I really donít want speakers in the living room but I told her if this amp works it would make a good combo. Maybe paired with a Blusound streamer.

Also by better performance do you mean more power, less noise, more linear or more pleasant sound? Or all of the above.
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Old 29th November 2018, 03:36 AM   #10
Eli Duttman is offline Eli Duttman  United States
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Quote:
Also by better performance do you mean more power, less noise, more linear or more pleasant sound?
Technical details, if you will.

The amp employs a full pentode mode O/P tube, along with a global negative feedback (GNFB) loop. The NFB loop improves damping factor and lowers distortion. However, reducing open loop distortion, before NFB is applied, is important. The lowest open loop distortion for full pentode mode is realized by regulating screen grid (g2) B+ at a fraction of anode (plate) B+. In particular, highly irritating intermodulation distortion (IMD) is reduced. For this situation, a Zener diode stack plus the requisite passive parts should be good enough in regulating g2 B+.

In what I think was "penny pinching", a cap. (say 15 μF./400 WVDC) was left out from the 230 V. point to ground. That cap. decouples the voltage amplifier triodes from the O/P tubes and improves stability.

Just so it can be seen that the Chinese circuitry is not complete garbage, compare it to the provided Magnavox console amp schematic. Similarities abound. AAMOF, I can easily see following, for the most part, Magnavox and not the seller.
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File Type: jpg Magnavox SE 6BQ5 Console Amp.jpg (177.9 KB, 1225 views)
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