I am at fault of tagging along with an error (most cerainly, a typo) in Gonzalo's post. He recommends 725 mA for bias. I am sure he meant 725 mV or 72.5 mA. Accordingly, my quotes of other posters' recommendations should have been 500 to 600 mV or 50 to 60 mA. In any event, my previous post is irrelevant (no response needed, Gonzalo) as I bought a plate-voltage measuring gauge that came with all required formulas and charts.
Cheers.....................munosmario
Cheers.....................munosmario
I am interested to get 1 unit of MC-100B but was told of the quality issues and the capacitors being exposed.
I hope someone can show the photo of the underside (i.e. the pcb with the base cover open)
1. Are the components used are of good quality ? Which brand of coupling cap used ? WIMA ?
2. Can you tap the voltage to 230V
3. Is this a dual mono design ?
4. Are there enough space to modify the volume pot to step attenuator ?
5. Filtering capacitors using which brand ? Rubycon ? Nichicon?
I hope someone can show the photo of the underside (i.e. the pcb with the base cover open)
1. Are the components used are of good quality ? Which brand of coupling cap used ? WIMA ?
2. Can you tap the voltage to 230V
3. Is this a dual mono design ?
4. Are there enough space to modify the volume pot to step attenuator ?
5. Filtering capacitors using which brand ? Rubycon ? Nichicon?
For munosmario
Dear audioguya munsomario, I have a good friend twaker mod guru extraordinnaire (wheezer) he has a small lab at homr where he measures output, voltage distortion freq. response etc. etc. etc.
One day nwe tood back cover out measured all data, output input impedances etc. and concluded that to achieve a very excellent voltage of 425 plate volts for the output on triode we needed to feed the amp not more than 106 volts fo so, so I finally settled on 105 off about 104 out of the varias when amplifier is fully loaded and on.
Then with only 425 volts on the plate he established that a good NOS like Tung Sol willl easy do 70 to 75 mA at that voltage without a problem.
This consistently brings the sound qualit of the amp to a whole new level of excellence.
you do neeed to bring voltage down . . if you adjust output bias to these values with the very dangerous 575 to 600V plate voltage with no varias inline straight form grid at 120 to 124 Volts as it is here, the output tubes will be destroyed in weeks . . .
So decrease teh voltage for the plate and increase the bias current, sit back enjoy!!
One more thing I found out by experimentarion.
Best power tubes 6550 Tung-Sol NOS bar none.
Second best SHuguang GEK-KT88 (Genalex copies form SHuguang in China), a little glary but definetely much beter than anything else out there.
Then 6SN7 either Tung-Sol NOS 6sn7-GT or GTA or GTB circa 1960's, then also more rare more $$ RCA gray glass 6SN7 GT circa 1940's are simply wonderful and also Ken Rad 6SN7 black plates clear envelope, or a ocmbination thereof of the ones mentiones, remember when combining to go form outside to insid eof the amp in mirror image to match the channel (dual mono)
Then for the pre driver te best tube I have found for this amp is in this order:
1- GE 5751 black plates or gray plates
2- Sylvania 5751 W1 gray plates
3- Tungsram ECC-83 (hungarian tubes)
4- Telefunken ECC83 gray plates ribbed or smooth both very good
Definetely the 5751's providing a bit less gain a A LOT better tone, structure better top to bottom balance, etc. etc.
It goes very well with my California Audio Labs Alpha tubed DAC sporting very excellent Tungsram ECC-83 (12AX7 equivalent)
fed form the front connectors of the amp with silver cables, either PSC Australian made or Kimber silver KCAG or the KS series (not hybrid!! just silver only)
By now you realize i have spend a fortune playing with tubes and selecting the ebst tubes for this amp (in my taste in my system, room, speakers etc. etc.)
I am very pleased the way this amp performs bass in triode mode form the 6550 tubes simply amazing!!
The vocals, harmonic structure, top end, sense of space, rithm, pace, slam, and detail are simply outstanding.
you can further teak the amp by cnahging soem of the amps resistors and cpacitors by superior quality i am sure it will greatly still improve sound quality to the likes of the $5K and over likes.
Just now with different tubes sound simply stunning.
Worth every penny!!!
Hope this helps.
Gonzalo
Dear audioguya munsomario, I have a good friend twaker mod guru extraordinnaire (wheezer) he has a small lab at homr where he measures output, voltage distortion freq. response etc. etc. etc.
One day nwe tood back cover out measured all data, output input impedances etc. and concluded that to achieve a very excellent voltage of 425 plate volts for the output on triode we needed to feed the amp not more than 106 volts fo so, so I finally settled on 105 off about 104 out of the varias when amplifier is fully loaded and on.
Then with only 425 volts on the plate he established that a good NOS like Tung Sol willl easy do 70 to 75 mA at that voltage without a problem.
This consistently brings the sound qualit of the amp to a whole new level of excellence.
you do neeed to bring voltage down . . if you adjust output bias to these values with the very dangerous 575 to 600V plate voltage with no varias inline straight form grid at 120 to 124 Volts as it is here, the output tubes will be destroyed in weeks . . .
So decrease teh voltage for the plate and increase the bias current, sit back enjoy!!
One more thing I found out by experimentarion.
Best power tubes 6550 Tung-Sol NOS bar none.
Second best SHuguang GEK-KT88 (Genalex copies form SHuguang in China), a little glary but definetely much beter than anything else out there.
Then 6SN7 either Tung-Sol NOS 6sn7-GT or GTA or GTB circa 1960's, then also more rare more $$ RCA gray glass 6SN7 GT circa 1940's are simply wonderful and also Ken Rad 6SN7 black plates clear envelope, or a ocmbination thereof of the ones mentiones, remember when combining to go form outside to insid eof the amp in mirror image to match the channel (dual mono)
Then for the pre driver te best tube I have found for this amp is in this order:
1- GE 5751 black plates or gray plates
2- Sylvania 5751 W1 gray plates
3- Tungsram ECC-83 (hungarian tubes)
4- Telefunken ECC83 gray plates ribbed or smooth both very good
Definetely the 5751's providing a bit less gain a A LOT better tone, structure better top to bottom balance, etc. etc.
It goes very well with my California Audio Labs Alpha tubed DAC sporting very excellent Tungsram ECC-83 (12AX7 equivalent)
fed form the front connectors of the amp with silver cables, either PSC Australian made or Kimber silver KCAG or the KS series (not hybrid!! just silver only)
By now you realize i have spend a fortune playing with tubes and selecting the ebst tubes for this amp (in my taste in my system, room, speakers etc. etc.)
I am very pleased the way this amp performs bass in triode mode form the 6550 tubes simply amazing!!
The vocals, harmonic structure, top end, sense of space, rithm, pace, slam, and detail are simply outstanding.
you can further teak the amp by cnahging soem of the amps resistors and cpacitors by superior quality i am sure it will greatly still improve sound quality to the likes of the $5K and over likes.
Just now with different tubes sound simply stunning.
Worth every penny!!!
Hope this helps.
Gonzalo
Thanks, gonzalo. The results of your trials with your "wizzard" friend, namely, 104 volts AC power (variac reduced), 425 volts DC plate voltage, and 72.5 mA bias, do they apply basically the same to the Shuguangs (KT88-98 and GEK-KT88) as to the Tungsol 6550 NOS? Or some agjustments may be necessary? Have you tried he Shuguand KT-88 solid plates (Penta labs and perhaps sold under some other private label)? I have a set of both the KT88-98's (three hole plates) and the Penta solid plate variety...I learned about the Sophia from your post.
Thanks again..........munosmario
Thanks again..........munosmario
Gonzalo, one more question. Do you happen to know or can you somehow acertain if the Yaqin MC-100B is Class A or Class AB? I have seen it advertized as one or the other by different vendors. Canada's Grant Fidelity and the Hong-Kong crowd refer to it as Class A (but I am a bit aprehensive as these vendors appear to be using hyped up specs like claiming power at 65W ultralinear and 32W triode (from the Yaqin factory's 60W and 30W respectively). Also Grant Fidelity* states that you can by-pass the preamp section using front input when that is not the case--anyone able to read the schematics can see that only the input switching stage is by-passed and the front stage is still in the amp circuit (reason why the quality of the 12AX7 tubes is still important even if you use a separate audiophile preamp). As you know, knowing the right amp class is important as power tubes can run at significantly higher bias when used in a Class A amp circuit.
Thanks & cheers......................munosmario
* Grant Fidelity's claims appear under the discontinued products in GF's website (it seems they stop selling their private label version a few months ago but still recommend it strongly).
Thanks & cheers......................munosmario
* Grant Fidelity's claims appear under the discontinued products in GF's website (it seems they stop selling their private label version a few months ago but still recommend it strongly).
Koifarm said:
I have read that the 6SN7 stage, Q2 & Q4 on the schematic might be running too low of current under 2ma when it should be around 9ma according to the datasheet to keep it linear. Here's an interesting observation article on the Yaqin translated from french:
http://forums.tabcrawler.com/index.php?topic=4903.0
What did you notice when you changed those caps? What value did you go from and to? I think mine has 220nf caps I was thinking of going to 1uf. Are these the only caps you changed?
What is the difference bewteen the KT-90 vs KT-88? Is it possible to use 6550 in this amp?
The Caps change give a deeper bass.
If you choose too high capacity for C6 and C7 then the output transformer got in saturation. 0.47 uf worked for me great and the Clarity Caps SA type gives then a bass i like most.
KT90 has more power and more control. 6550 runs also good in the yaqin MC100b.
Ronny
If you choose too high capacity for C6 and C7 then the output transformer got in saturation. 0.47 uf worked for me great and the Clarity Caps SA type gives then a bass i like most.
KT90 has more power and more control. 6550 runs also good in the yaqin MC100b.
Ronny
Thanks Ronny.
I noticed the Macintosh MC30 monoblocks have .47uf coupling caps off the power amp stage also. I will defintely give it a try.
Have you found that 6sn7 might be working too low of operating point?
I think there is about 515v to the plates of my 120v model to that guy that posted about the plate voltage. Isn't this well within the spec of the tube < 800 volts?
I noticed the Macintosh MC30 monoblocks have .47uf coupling caps off the power amp stage also. I will defintely give it a try.
Have you found that 6sn7 might be working too low of operating point?
I think there is about 515v to the plates of my 120v model to that guy that posted about the plate voltage. Isn't this well within the spec of the tube < 800 volts?
Hi Duncan, I know long time is passed since you published this post, but I would like to know if full image is still available.
If yes, could you plese send me a copy to eddi at frigos dot it ?
Thank you in advance and best regards!
Long term report
Well, I bouhgt my MC-100B in Feb 08, and it's now August 2010 and I've not had one iota of trouble with it. I've made no modifications, except for a little liquid electrical tape to the top of the exposed capacitors, just in case. I've run through a bunch of tubes too... had a set of RCA 12AX7's go microphonic on me, then switched to EH and then to repro mullards. I actually like the EH 12AX7's better in this amp, there's a little more bass extension. I put the mullards in my phono stage, and they sound really sweet there.
I had JJ Tesla KT88's and the bass response was stunning... but I had the bias set to what the manual recommended... and burned them up pretty quickly. Less than a year. For a while I was hearing a weird noise whenever the amp was turned on from cold and was warming up... thought nothing of it... eventually I was rocking out to something in the kitchen and I suddenly heard horribly loud crackling coming from my right speaker. Rushed into the room and the far right tube looked like a fireworks display. hit the power switch and let everything cool down.... tube was fried (literally, all the labeling turned scorchy brown on that tube).... but I put the original Chinese tubes back in and she fired right back up, no problems, no damage. I biased to a little lower than recommended, and I've been running them since.
In the market for some Gold Lion repros next I think. I liked this amp so much I bought the MS-12B phono stage from Yaoin as well. If anyone is wondering and worried about the long-term reliability of these units... don't be. Except for tubes, I've had zero problems. And seeing as I listen to music at least 2 hours a day every day (sometimes up to 8 hours), and I use the tube amp to power my front speakers in my HT setup, I think going through one set of kt88's and one set of (used) 12ax7's is normal wear.
In short, I'm extremely pleased. The tubes that come with it aren't great and should be replaced with something better, but other than that this thing sounds spectacular and has given me zero problems.
Charles.
Well, I bouhgt my MC-100B in Feb 08, and it's now August 2010 and I've not had one iota of trouble with it. I've made no modifications, except for a little liquid electrical tape to the top of the exposed capacitors, just in case. I've run through a bunch of tubes too... had a set of RCA 12AX7's go microphonic on me, then switched to EH and then to repro mullards. I actually like the EH 12AX7's better in this amp, there's a little more bass extension. I put the mullards in my phono stage, and they sound really sweet there.
I had JJ Tesla KT88's and the bass response was stunning... but I had the bias set to what the manual recommended... and burned them up pretty quickly. Less than a year. For a while I was hearing a weird noise whenever the amp was turned on from cold and was warming up... thought nothing of it... eventually I was rocking out to something in the kitchen and I suddenly heard horribly loud crackling coming from my right speaker. Rushed into the room and the far right tube looked like a fireworks display. hit the power switch and let everything cool down.... tube was fried (literally, all the labeling turned scorchy brown on that tube).... but I put the original Chinese tubes back in and she fired right back up, no problems, no damage. I biased to a little lower than recommended, and I've been running them since.
In the market for some Gold Lion repros next I think. I liked this amp so much I bought the MS-12B phono stage from Yaoin as well. If anyone is wondering and worried about the long-term reliability of these units... don't be. Except for tubes, I've had zero problems. And seeing as I listen to music at least 2 hours a day every day (sometimes up to 8 hours), and I use the tube amp to power my front speakers in my HT setup, I think going through one set of kt88's and one set of (used) 12ax7's is normal wear.
In short, I'm extremely pleased. The tubes that come with it aren't great and should be replaced with something better, but other than that this thing sounds spectacular and has given me zero problems.
Charles.
G'day all, I found this site by accident after seeing a Yaqin MC-100B for sale on ebay for what seemed a preposterously cheap price for a valve amp. I've never owned a valve amp but have been intrigued by them for years. My solid state Exposure dropped it's guts recently and I'm in the market for a new 'en. My thoughts at the moment are leaning towards the MC-100B and the MS-11B phono stage. My main concerns are with the day to day running of a valve amp ( are there any "tricks of the trade " concerning maintenance?), system compatibility -I have a Musical Fidelity X-Ray CD player, a Rega turntable and Legend Acoustics Kama 5 speakers , these are similar to the Linn Kabers-designed by the same bloke. The paranoid cynic in me says that the price is too good to be true -there must be a catch! I'm also not sure about buying from overseas but I haven't really looked into it properly. All of this boils down to the question of is the MC-100B a viable alternative for a valve no-nothing like me?
output transformer modification
a good solution to increase current on yaqin mc-100b is put in parallel two serial section (0-4 and 4-8 ohms)
of secondary output (made by 4 secondary each)
so at last you have 8 secondary in parallel ad ratio from primary 4kohm to secondary 4ohm now is 100:1
this device now disappears from your scene
please try in UL mode
a good solution to increase current on yaqin mc-100b is put in parallel two serial section (0-4 and 4-8 ohms)
of secondary output (made by 4 secondary each)
so at last you have 8 secondary in parallel ad ratio from primary 4kohm to secondary 4ohm now is 100:1
this device now disappears from your scene
please try in UL mode
Attachments
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Hi guy! 
I have got a Yaqin MC100 and he sounds very good.
I have to change the KT88 with 4 Gold Lion, for now I have got the chinese KT88 tubes and changed the other ones
I have notice more airy sound with a simple DIY cable:
The TNT - TTS DIY mains cable
enjoy
I have got a Yaqin MC100 and he sounds very good.
I have to change the KT88 with 4 Gold Lion, for now I have got the chinese KT88 tubes and changed the other ones
I have notice more airy sound with a simple DIY cable:
The TNT - TTS DIY mains cable
enjoy
Current flow in 6sn7 tubes
Has anyone tried the mods suggested in the link:
Yaqin MC 100B Chinese Tube Amp Mods
to increase the above? It seem s the factory setting is way below optimal.
What difference have you measured or heard?
Has anyone tried the mods suggested in the link:
Yaqin MC 100B Chinese Tube Amp Mods
to increase the above? It seem s the factory setting is way below optimal.
What difference have you measured or heard?
Yaqin MC100
Hello to everyone. I should explain that I am new to this forum and new to valve HIFI. I have been looking to make an entry into valve based HIFI for a while and would like some advice please.
The Yaqin MC100 amplifier seems to offer a reasonable specification at a budget price. If this amplifier is worth a try, and comments seem to suggest it is, what speakers and CD player should I acquire to complete the bundle? I live in the UK.
Hello to everyone. I should explain that I am new to this forum and new to valve HIFI. I have been looking to make an entry into valve based HIFI for a while and would like some advice please.
The Yaqin MC100 amplifier seems to offer a reasonable specification at a budget price. If this amplifier is worth a try, and comments seem to suggest it is, what speakers and CD player should I acquire to complete the bundle? I live in the UK.
I too am new to valve hifi. Played bass guitar in many bands, but that was years ago. Always preferred tube instrument amps, as do virtually all serious musicians. I liked Ampeg.
I once heard a tube McIntosh system, three decades ago, and the memory is etched in my mind forever. So....after many years of solid state home stereo, I found a 2 year-old Yaqin MC100B in great shape for the princely sum of $366 US.
This is my first post on any hifi forum. I take all my toys apart, but know nothing about tube amps. So I am standing at the top of a steep, slippery slope. I will be reading voraciously. This thread has been very interesting. I am likely to "roll" some tubes. Perhaps some Gold Lions to start.
I once heard a tube McIntosh system, three decades ago, and the memory is etched in my mind forever. So....after many years of solid state home stereo, I found a 2 year-old Yaqin MC100B in great shape for the princely sum of $366 US.
This is my first post on any hifi forum. I take all my toys apart, but know nothing about tube amps. So I am standing at the top of a steep, slippery slope. I will be reading voraciously. This thread has been very interesting. I am likely to "roll" some tubes. Perhaps some Gold Lions to start.
I am going to read carefully through some earlier posts in this thread in which folks recommend certain voltage adjustments. Bear in mind I am a relative newbie. This amp has pairs of ports in the chassis so the user can place test leads in and measure voltage. This is adjustment of the (4) Kt-88 output tubes. There are also four ports into which a tiny (2.5mm) hex tool can be inserted to adjust voltage.
The voltage readings I got were:
1) 329 mv
2) 367 mv
3) 0.571 V
4) 315 mv
I believe #3 is simply a function of my meter's auto ranging, and that 0.571 V equals 571 mv.
Anyway......am I on the right track? Are these voltages ideally set in the 450 mv range? It seems to me I read something like "45" rather than the factory-set "55-60". This does not compare with the readings I am getting. If a figure of 45 is desired, are we talking 45 100ths of a volt? Help me out here. I will go back and re-read.
The voltage readings I got were:
1) 329 mv
2) 367 mv
3) 0.571 V
4) 315 mv
I believe #3 is simply a function of my meter's auto ranging, and that 0.571 V equals 571 mv.
Anyway......am I on the right track? Are these voltages ideally set in the 450 mv range? It seems to me I read something like "45" rather than the factory-set "55-60". This does not compare with the readings I am getting. If a figure of 45 is desired, are we talking 45 100ths of a volt? Help me out here. I will go back and re-read.
Ah hah! 10 ohm resistor. So this is why I am measuring about 350 mV at the test ports? And this means a "bias" of about 35 mV?
Okaaaay....... 35 mV bias is not enough. Factory says 55-60. Some guys say 40-45 for longer tube life. One guy says that's not enough.....resulting in a flabby bass. The bass my amp is making is flabby. Hmmmm.......
You are correct that 35mA (that is the amount of current going through the tube (read up on ohms's law)) is too little for a KT88. I think that in general a KT88 is fine with 50mA and with a good solid power supply and not too high a plate voltage 60mA is good. So go ahead and try 50mA which is 500mV on your meter. That might improve the sound some.
I don't know exactly why your phono stage damaged the amp, but it seems likely that it could have been an issue with grounding. I hate to blame the amp but some have observed all sorts of weird wiring mistakes in the Chinese amps in general. A quick look at the schematic which you posted on another thread seems to show that there is NO safety ground wire on the amp, i.e. it has a two prong power cord. This is something the shop where you had the unit repaired should have fixed without asking.
Here's the deal: it is possible that the amp or the phono stage is leaking voltage onto the chassis. If you connect the two together there will be a voltage difference between the two chassis and so the interconnect becomes a current carrying link. It was not intended for this purpose and will fry whatever is connected to it.
Plug in the phono stage and, using the AC voltage reading on your meter, put one probe on the ground ring of the RCA jack and the other to the ground pin on the wall outlet. If there is an AC voltage reading there try changing the orientation of the plug (assuming it is a non grounded plug). Do the same thing for the power amp. There should be no AC voltage reading at all on the chassis or the RCA jacks which should be internally connected to the chassis. If you get an AC voltage reading on the amp take it back to the shop!
I don't know exactly why your phono stage damaged the amp, but it seems likely that it could have been an issue with grounding. I hate to blame the amp but some have observed all sorts of weird wiring mistakes in the Chinese amps in general. A quick look at the schematic which you posted on another thread seems to show that there is NO safety ground wire on the amp, i.e. it has a two prong power cord. This is something the shop where you had the unit repaired should have fixed without asking.
Here's the deal: it is possible that the amp or the phono stage is leaking voltage onto the chassis. If you connect the two together there will be a voltage difference between the two chassis and so the interconnect becomes a current carrying link. It was not intended for this purpose and will fry whatever is connected to it.
Plug in the phono stage and, using the AC voltage reading on your meter, put one probe on the ground ring of the RCA jack and the other to the ground pin on the wall outlet. If there is an AC voltage reading there try changing the orientation of the plug (assuming it is a non grounded plug). Do the same thing for the power amp. There should be no AC voltage reading at all on the chassis or the RCA jacks which should be internally connected to the chassis. If you get an AC voltage reading on the amp take it back to the shop!
The power cord is a standard cord, separate from the amp chassis. It is a thick thing that includes ground prongs. There is a male ground prong along with the hot and neutral prongs on the amp chassis where the cord plugs onto it.
Plug the phono preamp into the RCA connectors at the front of the amp? This is perhaps what fried the amp in the first place, and it would cover the connector so I could not get at it with a test probe. Or are you suggesting that I check resistance between the ground pole on the chassis where the power cord plugs into it, and the outer (ground?) ring of the RCA jacks in the front of the amp (0.6 mV)? That would make sense.
Or perhaps I should disconnect the power cord from the amp chassis, plug the powered preamp into the input connector at the front of the amp (0.6 mV), and check to see if there is voltage at the negative pole where the power cord goes?
This I don't get. Again, the power cord is a modern cord, separate from the amp chassis, with three conductors. They are oriented in a triangular shape at the amp end.
Amp end? Sorry, I do not follow.
Also, every time I have ever used my multimeter to look for voltage, I have found it. I think I can find voltage in a tree or sidewalk. A tiny amount, but it's always there.