• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Yaqin MC-100b schematic diagram

Hi there to all you experts out there. I have recently bought a Yaqin MC100b integrated amplifier from eBay. I have not hooked it up yet since I have read in quite a few forums that some of the bias from the factory were set wrong and the amp works for a few months and either blow resistors/caps or valves. I was wondering if any of you have had such experience from Yaqin amps and if any of you had owned or still owns the MC-100B and if you have a circuit diagram? :D As you can see from my introduction, I am a novice at valve stuff and would like to know how to "tune" the bias - either current or voltage to the valves. If any of you have some suggestions, I would very much appreciate it. Cheers.
 
Yaqin MC-100B circuit diagram

You might find this useful.
I have one of these amps, a most excellent sound.
Using one in the UK means I need to step down the mains 240volt supply or the heaters run at 7.4v and every thing is a bit stressed. I use a buck transformer this works very well.

Duncan

sorry about the quality, email me if you want the original jpeg. 1.24Mb
 

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MC-100b WARNING

Hi aristoctrat and other owners of the Yaqin MC-100b.

One exemplar of this amp have passed for my workbench and I have remarked that it was lethal for the operator.

The power supply electrolytic capacitors, situated outside the case, are without isolation at the top and in two of them there was the full HT rail ( ~ 500 V ).

Please inspect with a voltmeter, the voltage between the chassis and the top of the capacitors and if you measure the same voltage, make some insulation in plastic and glue it to the top of the capacitors.

A very dangerous amp... :att'n:

Regards
 
Re: Yaqin MC-100B circuit diagram

halx00 said:
You might find this useful.
I have one of these amps, a most excellent sound.
Using one in the UK means I need to step down the mains 240volt supply or the heaters run at 7.4v and every thing is a bit stressed. I use a buck transformer this works very well.

Duncan

sorry about the quality, email me if you want the original jpeg. 1.24Mb

Hi Duncan,
Could you send me the original jpeg (bartek at hfm dot pl)? Thank You in advance!
Crategus
 
bias

I had heard the MC-10L blew parts (resistors) due to incorrect bias settings, not the 100B.

Supposedly if you buy from the Canadian dealer, each unit is tested and adjusted before it is shipped, and it comes with a 1 year full replacement warranty and 2 years of free labor after that. Plus it comes with a translated manual.

I just bought the MC-100B from that guy.... so I'll let you know more when it gets here!

Charles.
 
aristocrat said:
Hi there to all you experts out there. I have recently bought a Yaqin MC100b integrated amplifier from eBay. I have not hooked it up yet since I have read in quite a few forums that some of the bias from the factory were set wrong and the amp works for a few months and either blow resistors/caps or valves. I was wondering if any of you have had such experience from Yaqin amps and if any of you had owned or still owns the MC-100B and if you have a circuit diagram? :D As you can see from my introduction, I am a novice at valve stuff and would like to know how to "tune" the bias - either current or voltage to the valves. If any of you have some suggestions, I would very much appreciate it. Cheers.

I sold several Yaqin MC100B. The bias was always set between 40 and 45 mA with the bias on 60mA the tubes will burned out after 500 hours. With the 40/45 mA bias they will last for more then 2000 hours. The sound is the same.
 
Doesn't matter. Set it for what mode you use most, at minimum volume. I've found that triode/UL and volume don't really make a difference - the bias doesn't change... but the English instructions do say to make sure the volume is all the way down.

I bought mine from Canadian HiFi Online.. .a little more expensive, but offers a 3 year warranty and pre-adjusts the bias and tests each unit before shipping. Customer service is amazingly good.

Charles.
 
Post #9

Hi Charles, I am of the same opinion. The 100b is superb especially taken into account value for money. I think if you were to buy all the components and build it yourself, you wouldn't be saving much at all. This amp is incredible. The details are good, perhaps also due to the fact that I upgraded my CD player to a Teac VRDS-20 and got some decent signal and speaker cables. I own a pair of B&W220i and even those are showing inadquacy. Hence I shelled out to buy a pair of Altec 604-8G. I know this Hi-Fi thing is intoxicating, and I think you'll find that by upgrading one component, you'll keep upgrading since it will show flaws in other components. But this is all worthwhile for me. I am stoked about my system for now. I think the next upgrade would be to change the 12AX7s and the 6SN7s to Mullards to see if this really makes much of a difference in sound. Anybody out there whose done this and found any significant difference?
 
Okay guys than tell me why the bas is so bad?

I had a harman kardon 730 twin powered receiver which is about 2500 years old and that one outsound this eggboiler chinese thing.

I brought this because the harmans selector switch is gone and it's lights gone for almost a 100 years ago but it's a big big bang,
This thing moves two times looked the pic.

What can I do? Does the external preamp would improve my bas with loudness controll or?
 

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bas? You mean bass?

Swap out the stock chinese 12AX7's for Electro Harmonix tubes, and that will tone down the brightness and make the amp much warmer. If you want punchy bass and a really rich sound, swap out the 6n8p's for Sylvania 6sn7 chrome domes. Also, run ultralinear instead of triode for more bass.

With this setup and my Cerwin Vega VS150 speakers I can rattle pictures off the walls during action flicks!

The sound is really limited by the chinese brand tubes, but the circuit design is excellent.

Charles.
 
ChopperCharles said:
bas? You mean bass?

Swap out the stock chinese 12AX7's for Electro Harmonix tubes, and that will tone down the brightness and make the amp much warmer. If you want punchy bass and a really rich sound, swap out the 6n8p's for Sylvania 6sn7 chrome domes. Also, run ultralinear instead of triode for more bass.

With this setup and my Cerwin Vega VS150 speakers I can rattle pictures off the walls during action flicks!

The sound is really limited by the chinese brand tubes, but the circuit design is excellent.

Charles.

Yes I mean bass, sorry for my incredible bad spelling. So you know this amp very well?

You wrote
"With this setup and my Cerwin Vega VS150 speakers I can rattle pictures off the walls during action flicks!"

That's ecxacly what I wan't but with the big bang! :)

So, are you very sure about this changing thing?

Hej, I just find out that I don't have the 6n8p's but do have the 6SN7and four of it.
 
Regarding the Bias setup for the tubes, from what I can gather, the instruction manual says to setup the bias at 55-60mV, however other members have indicated setting it up at 40-45mA. Which one should I use? Are they the same? Just wondering is it a matter of switching the multimeter to DC current to read the current flow on the same test posts rather than measuring the DC voltage? or is it trickier than this? Cheers guys.
 
Good question,voltage and current are not the same thing. If I had a schematic I could figure out what the voltage across the resistor translated in terms of current draw. LETS SEE IF I CAN REMENBER OHMS LAW. ITS BEEN ABOUT 40 YEARS. R=E/I R=6X10-1/45X10-3= A CATHODE BIAS RESISTOR OF ABOUT 13OHMS APPROX but this doesn't help us because we have no schematic! Thats about as much help as I can give you. Perhaps someone else can take over from here
 
aristocrat said:
Regarding the Bias setup for the tubes, from what I can gather, the instruction manual says to setup the bias at 55-60mV, however other members have indicated setting it up at 40-45mA. Which one should I use? Are they the same? Just wondering is it a matter of switching the multimeter to DC current to read the current flow on the same test posts rather than measuring the DC voltage? or is it trickier than this? Cheers guys.

The manual says 550mv-600mv with is a current of 55-60mA thrue a 10 Ohm resistor. You just measure the DC voltage on the testpoints and devide it with 10 and now you have the biascurrent.

40-45mA measures on the testpoinst 40-45 x 10 = 400-450mVDC.
This current has proven that the lifetime of the tubes will be about 2000 hours while 60mA current burned up the tubes in 500 hours. I have a lot of experience with the MC100B.


keithgreenhalgh said:
Good question,voltage and current are not the same thing. If I had a schematic I could figure out what the voltage across the resistor translated in terms of current draw. LETS SEE IF I CAN REMENBER OHMS LAW. ITS BEEN ABOUT 40 YEARS. R=E/I R=6X10-1/45X10-3= A CATHODE BIAS RESISTOR OF ABOUT 13OHMS APPROX but this doesn't help us because we have no schematic! Thats about as much help as I can give you. Perhaps someone else can take over from here

U(Voltage in Volts)= I(current in Ampere) x R ( resistance in Ohm )

Schematic of the yaqin MC100b in Post#2
 
Thank you gentlemen for such great help. Now, all I need to do is measure the DCV across the test points to measure 0.4 - 0.45V should be fine then? How about the schematics saying an input voltage of AC220V, mine is AC240V since I live in Australia. I have lifted the lid up on the transformers, and they did have stickers saying its 240VAC windings. Should the voltage still be the same across the test points or would they vary due to the input voltage being different? Sorry about my ignorance here. I don't think that matters, but just thought I'd check with the experts here. Cheers, Spencer