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Chinese stuff - YAQIN ?

M

micdon

Active Member
Hi,

The tube hype doesn't stop here :-)
After working under the hood of almost all American brands I'm now getting in a YAQUIN EL34 amp that buzzed and stopped working. One of my colleagues bought an expensive Chinese headphone amp that popped a cap after less than one hour operations so I'm a little biased here.

Any repair experiences here to share with YAQIN ?
I don't want to start a generic Chinese vs US discussion :nono:

Cheers
Mic
 
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The headphone amp was brand new. Not sure how old the YAQIN is.
Just to mention: The replacement of the headphone amp worked out very well and uncomplicated. Obviously minus long waiting times. I'm curious if anyone had one of these YAQIN EL34 guys on his bench. I will post an update with some pictures once I had a chance to look on it. What's odd is that there doesn't seem to be an external facing fuse. I hope there is one under the hood which would be a starting point. Beside of that I'm expecting to see some LM317s or Zeners or other modern stuff which easily breaks. I have used these components and beside of the advantages they bring they also tend to fail quick and fatal if e.g. a tube arcs.
 
Check your mains voltage, if it is higher than 120V, that could potentially cause problem for many Chinese-made amps including the Yaqin, which commonly have PT wired for "110V-120V". Say if the PT is actually designed for 110V and your mains is 125V, that would result in a significant increase of the HV and filament voltages, which may lead to component failures. Of course, plain old poor QC could result in cold solder joints, poor/in-correct wiring, etc.
 
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I haven't had one on the bench for repairs, only to modify.....eventually was rebuilt using only the transformers as I didn't have enough room to do what I wanted in the chassis as it was.

Early ones did have an issue where a cathode resistor would fry, but I think they fixed that in later versions.

Do check the power supply rating as many sellers will send what they have regardless, I specifically asked for 240v mains even though ours is 230v on paper. they can order any rating from the Yarqin factory. Lift the cover and it should be stamped in white on top of the transformer.
 
Later versions (if it is one of the MC10 family) have extra B+ fuses for each channel. Speaking for the MC10 series, they are not that bad and only show problems one would expect nowadays with the build standard of the tubes. I have owned two such amplifiers and fitted Electro-Harmonix 6CA7's. Owners without prior knowledge of tube amplifiers seem to be oblivious to the importance of regular checking bias levels in the output stages. I did a kind of guide for these amplifiers, collating various modifications and improvements made but more importantly, giving a better schematic to assist in component location and replacement. The fault you give for the amplifier sounds like an overload has occurred in the output stages probably by a bad tube. It may have taken out the cathode monitor resistor, hopefully not the output transformer but this can be verified by measuring the voltages around each output tube holder.
As suggested in the guide, one can even use the internal plugs to route cross over the left/right circuits to aid fault find if you are lucky to have enough cable lengths.

http://homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.pdf
 
I don't have direct experience, since I'm not a repair tech.

But I remember awhile back I visited my local tech in town (whom I trust without reservation).

He had a Yaqin amp (the KT88) one on his bench that kept blowing power tubes. He opened it up and we had a good laugh the the transformers inside. On the outside, huge transformer covers, on the inside puny little transformers of dubious quality.
 
Celt said:
Speaking of high AC...mine is a rock solid 126 VAC each and every day! :yikes:
Click to expand...

Zowey! I thought my occasional 123 was bad. Well, rock solid is good though, mine can be 117 on a really hot day to 123 or so on mild days. Air conditioners I suspect.
 
About the repair tech point: I do tubes for fun and not for money. If someone knows a good repair tech in NJ that doesn't suck please PM and I might send some work and customers over. The thing is that it's getting more and more stuff in here. No matter how bad the condition (even if it's a bag full of rusty parts) it comes out as nice and good sounding amp.

Let's close the China chapter with a couple of pictures and a quick summary. It's a Yaqin 34D with 4xEL34 and 4x6AK5 alias 6J1. It used to work fine for years based on the owner.

Under the hood:
Nothing special beside of a ton of sloppy and bad solder joins and an unnecessary amount of cheap components that are in some cases weirdly soldered together. Special is that there are bias pots for each output tube individually and a fuse for B+. Also interesting is that it can be switched between triode and ultra linear mode. I haven't opened the transformer covers - sorry.

Diagnosis work:
- Testing all tubes - all good
- Testing the fuses - looked good but was bad
- Root cause for the blown fuses - sloppy solder joints (110/220 switch)
- Changed the fuse and adjusted all tubes to be equally biased
- Dummy Load and Scope and full load for an hour sweeping 20hz to 20Khz

Ready to get home to his owner

How does it sound ?
Sounds like it measures - boring and not really stunning. Measured output is 25W RMS per channel (UL Mode)
Frequency response low end is bad. Less than 5 watts and clipping at 50 hz. Other than that it's quite ok and it looks nice on the outside of course with Chinese blue LEDs for those who like them.

In summary I would recommend to spend the 400 bucks on well known vintage stuff and to find someone that does a recap for some beers...





Cheers
Mic
 
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To me, the difference between the stuff coming from China and the stuff produced by small American and European companies (like mine) is that we care - or at least I do. The stuff I make has my name on the front and I want it to be something I can be proud of. I've been an audiophile since I was a kid; I've been listening to vinyl since I was a kid; I've worked in various roles in the music industry; I'm still passionate about music and sound quality. Maybe I'm a bit sad, but this stuff actually matters to me.

Somehow, I suspect that much of the stuff coming from China is made by people who have no idea what it is they're making and have no idea about sound quality, and don't care as long as someone's buying the stuff and they're making some money.

On the plus side, much of the stuff from China is incredibly cheap - much cheaper than we can make.
I have no experience of YAQIN but I would (by default) expect it to conform to the Chinese norm.
 
micdon said:
...


How does it sound ?
Sounds like it measures - boring and not really stunning. Measured output is 25W RMS per channel (UL Mode)
Frequency response low end is bad. Less than 5 watts and clipping at 50 hz. Other than that it's quite ok and it looks nice on the outside of course with Chinese blue LEDs for those who like them.
Click to expand...

1) Boring and UL kinda tend to go together :-p (well, OK, IMO -- ya want emotion outta yer electronics? Go SE)
2) LF response behavior sounds like it is all in the output iron. Not necessarily a deal killer from my perspective.
3) I (still) like blue LEDs ;-)
 
FYI, I've been running a Yaqin MS-12B phono stage and a MC-100B integrated amp since 2008 with not a single problem. I've even roasted a tube or two (lightning show), but the amp survived it perfectly. Been running for more than a year now with Tung Sol KT120s biased at 1.0v and it sounds nice and sweet. It will take a beating and just keep performing.

Charles.
 
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