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Old 23rd December 2009, 02:48 AM   #1
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Default New to Tubes, just bought first tube amp

Hello. I have been the proud owner of a Yaqin MC10-L for about three weeks now. It is replacing an older Pioneer Elite solid state amp. Overall I LOVE it. It is a gorgeous amp and I am sure that many of you hear have an appreciation for just how beautiful tubes are. I am somewhat familiar with electronics (took it in high school and tinkered around as a teen) but there is a LOT to know about tubes. I have spent most of the day reading up on them. My dad is a tube guy but from a guitar players perspective. He was thinking about getting me some upgraded tubes for Christmas (or soon thereafter). Here are some specs on the amp:

"The Yaqin MC-10L, according to my friend Stuart who's an electronics and audiophile guru, is a very simple design that's quite similar to the Dynaco ST70, a classic audiophile tube amp sold from the 1950s into the 1970s. Output power is about 52 watts (at 8 ohms) per channel using four EL-34-B tubes for the power amplification stage and four 6N1's, a common Russian/Chinese tube, for the preamp section. (There are speaker connectors on the back to run it at 4 or 8 ohms.)"


from this page:
coolcatdaddy: Yaqin MC-10L Amp - An initial review


There is a comment on that page suggesting uppgrades:
"Bob L said... I picked up an MC-10L from the same seller around Christmas time. I thought it was amazing, until I rolled some Russian 6n1p's into the preamp stage and some EH 6CA7's into the output stage...wow, what a difference. Upgrade the tubes on that bad boy coolcatdaddy, you dont know what youre missing"


But my sent me this link warning against the 6N1ps:
Print Page - Replacement Tubes for Chinese 6n1


He said they run hot.


I am open to any suggestions and would just love any pointers to technical info. I like the idea of toying with the sound with different tubes and I can't deny that some tubes are just prettier than others. I know that is a minor concern but I could just stare at my amp all day.


I don't quite understand why one tube would replace another and why one would be better than another. I don't want to endanger the amp (although it was a hell of a deal) but would like to have fun with it.


Also it sound great as is IMO. I hear some tiny bits of background noise but turning it off and on has seemed to resolve it. The amp and new speakers have been playing 24/7 on opinions that I should "burn in" both.



The new speakers I bought to go with the new amp are some Focal 716Vs. I love the sound of them as well.



While I am at it here are some pictures of my new gear. The input device is a Roku M2000 Soundbridge. I have been going back and re-encoding my entire library to FLAC for the new setup.


bedroom audio

Click the image to open in full size.
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Old 23rd December 2009, 04:37 AM   #2
rman is offline rman  Canada
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Cool amp.

If you want to take this hobby to it's fullest, get a killer turntable and phono stage. there is nothing like valves and vinyl!
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Old 23rd December 2009, 05:15 AM   #3
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I actually have been a DJ for about 15 years. Half of my living room is filled with crates of vinyl. They aren't "audiophile" tables though, they are workhorses. Technics 1210s.

Click the image to open in full size.
Click the image to open in full size.
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Old 23rd December 2009, 07:34 AM   #4
dhaen is offline dhaen  Europe
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I've repaired these and can say that they are better than many Chinese amps. (Build and performance).
Glad to see you have the later version with the holes for bias adjustment. As the output valves/tubes age you will need to check this.
Underneath those transformer covers are conventional EI transformers, but they are of a fairly reasonable size.
Like several other Chinese amps, most imports into the UK are rated at 220v. When run at 240v, they get stinking hot. Hopefully your mains is closer to 110v than 120v.
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Old 23rd December 2009, 07:38 AM   #5
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Quote:
Originally Posted by dhaen View Post
I've repaired these and can say that they are better than many Chinese amps. (Build and performance).
Glad to see you have the later version with the holes for bias adjustment. As the output valves/tubes age you will need to check this.
Underneath those transformer covers are conventional EI transformers, but they are of a fairly reasonable size.
Like several other Chinese amps, most imports into the UK are rated at 220v. When run at 240v, they get stinking hot. Hopefully your mains is closer to 110v than 120v.
What is a conventional EI transformer? They seem very heavy as most of the weight is on the back end. Don't all household currents fluctuate in America between 110 and 120? Is one better than another? Is there anything I can do about that? And any suggestions on tubes themselves? I did the bias adjustment when I got the amp although I don't really have a clear idea what that is doing. Thanks.
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Old 23rd December 2009, 02:55 PM   #6
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Quote:
Originally Posted by josefgabriel View Post
What is a conventional EI transformer? They seem very heavy as most of the weight is on the back end. Don't all household currents fluctuate in America between 110 and 120? Is one better than another? Is there anything I can do about that? And any suggestions on tubes themselves? I did the bias adjustment when I got the amp although I don't really have a clear idea what that is doing. Thanks.
The round transformer covers imply that the transformers are toroidal (doughnut shaped); EI transformers are more conventional looking with a vertical or horizontal stack of laminations with the coil windings inside. The core laminations in an EI tranformer are actually "E" and "I" shaped. Since you appear to be keen on getting a tube lesson, search this forum for EI transformers and toroidal transformers. In general, toroidal transformers can be smaller for a given power rating, are more efficient, but saturate abruptly when overdriven.

Residential mains power has slowly crept up a little over the decades.
If the transformer primary windings are designed for 110V (US) or 220V (EU, etc) the amp with run a little hot (above it's nominal power ratings) when the mains voltage in your house is higher (which is typical today, usually 120V) and can sometimes run the tubes a little closer to their power limit. The amp will run a little hot, produce more output power, sometimes sound better, and have a slightly reduced tube life.

Adjusting the bias pot (voltage adj) adjusts the idle current through the output tubes by changing the negative voltage on the control grid of the tubes. Your amp is fixed bias, another interesting thing to search for here.
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Old 23rd December 2009, 06:44 PM   #7
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Quote:
Originally Posted by boywonder View Post
The round transformer covers imply that the transformers are toroidal (doughnut shaped); EI transformers are more conventional looking with a vertical or horizontal stack of laminations with the coil windings inside. The core laminations in an EI tranformer are actually "E" and "I" shaped. Since you appear to be keen on getting a tube lesson, search this forum for EI transformers and toroidal transformers. In general, toroidal transformers can be smaller for a given power rating, are more efficient, but saturate abruptly when overdriven.

Residential mains power has slowly crept up a little over the decades.
If the transformer primary windings are designed for 110V (US) or 220V (EU, etc) the amp with run a little hot (above it's nominal power ratings) when the mains voltage in your house is higher (which is typical today, usually 120V) and can sometimes run the tubes a little closer to their power limit. The amp will run a little hot, produce more output power, sometimes sound better, and have a slightly reduced tube life.

Adjusting the bias pot (voltage adj) adjusts the idle current through the output tubes by changing the negative voltage on the control grid of the tubes. Your amp is fixed bias, another interesting thing to search for here.

I am pretty sure my amp does have bias adjustments. You don't even need to take the cover off. There are holes for the probes for each vallve and its corresponding pot. The first thing I did when I uppacked it is do a bias adjustment.

Here is the guide I followed to do the bias adjustment:
http://yaqin.slickpepper.org.uk/wp-c...adjustment.pdf

Although in the guide you need to take the cover off the newer ones have the holes.

Here is a picture showing the holes:
Click the image to open in full size.

I have been looking for more specs on the transformer. They do not appear to be torioids:
"First of all, I was a little disconcerted about the seeming hollowness of the cans over the transformers, particularly the outputs. It was my assumption that such large cans hid hideously small iron. The amp has good heft to it, so I figured that Yaqin latched to the age old trick of increasing mass by installing thick plates or even lead bars (I have seen that before). Well, I was dead wrong. While the transformers are not toroid, as one would expect from the cans, they are generously large and of exceptional quality. The individual laminations are incredibly thin, which (based on experience) is a Good Thing™."

And a (bad) Chinese translation from a dealer:
"Output transformer uses the Japanese import audio frequency
special-purpose silicon steel plate (0.35mm thick) and the high strength enamel- insulated wire
and specially circles the system craft manufacture, causes this machine frequency sound width,
high guarantees this machine, center, the low frequency timbre good, insightful is powerful. "

I will definitely do some reading now as you suggested. But still no suggestions for tubes?
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Old 24th December 2009, 01:42 AM   #8
rman is offline rman  Canada
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Hi.

When Boywonder said that your amp has fixed bias, he did not mean non adjustable. A separate negative power supply is connected to the tubes grids and this is what you are adjusting. This is in contrast to the more usual cathode bias where the voltage drop across a resistor from 0 volts to the tubes cathode makes the cathode more positive than the grid which is held at 0 volts.

Cheers.

Rolf.

P.S.

Wish I had as big a vinyl collection as you!
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Old 24th December 2009, 01:54 AM   #9
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Quote:
Originally Posted by rman View Post
Hi.

When Boywonder said that your amp has fixed bias, he did not mean non adjustable.
Exactly. Although it's counter-intuitive, fixed bias means you can adjust the bias current/voltage (with pots) and cathode bias does not have the adjustment.
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Old 24th December 2009, 04:20 AM   #10
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Quote:
Originally Posted by rman View Post
Cool amp.

If you want to take this hobby to it's fullest, get a killer turntable and phono stage. there is nothing like valves and vinyl!
Don't waste your money chasing the vinyl hype.
You'll spend a fortune for cartridges and tone arms only to play garbage pressings. Unless you want to listen to so called "audiophile" recordings that often are lousy performances by mediocre talent.
Then there is the total Voodoo nonsense that passes for good mechanical design of the turntable purveyors.Just go back to reel to reel tape. Or just be satisfied with CD.
I went that route...had various Koetsu cart. three were in fact especially wound by Mr. Sugano to match the tonearm - turntable that I bought from him directly at CES. Then a series of Madrigal pieces of junk hanging off the tonearm adding mass while masquerading as phono cartridges.. All the while chasing this mystical scent I could have been spending money to buy music to listen to.
Music is vastly more important than equipment... one is the excuse for the other!
Opera for all...............music est totus!
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Last edited by tympani1d; 24th December 2009 at 04:22 AM.
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