Andrew,
Sorry for the slow response, but i have been away for a few days. My original problem was a failed tube that caused a cathode resistor to fail. I replaced the cathode resistors in the left channel and also the valves but still no sound. Thanks to the people on this site I was advised to do a series of checks and eventually I found that is was a small piece of metal rubbish that had lodged in the input selection switch. Two totally unrelated problems I would suggest. Bottom line was that it was a short in the switch. I think that when I turned the amp upside down to make it easier to replace the cathode resistors I have caused the problem in the switch. As part of the process of eliminating likely causes I removed the switch and the metal bit fell onto my bench. My problem was solved. A similar problem with errant metal bits has also been reported.
Regards Mike.
Sorry for the slow response, but i have been away for a few days. My original problem was a failed tube that caused a cathode resistor to fail. I replaced the cathode resistors in the left channel and also the valves but still no sound. Thanks to the people on this site I was advised to do a series of checks and eventually I found that is was a small piece of metal rubbish that had lodged in the input selection switch. Two totally unrelated problems I would suggest. Bottom line was that it was a short in the switch. I think that when I turned the amp upside down to make it easier to replace the cathode resistors I have caused the problem in the switch. As part of the process of eliminating likely causes I removed the switch and the metal bit fell onto my bench. My problem was solved. A similar problem with errant metal bits has also been reported.
Regards Mike.
How is the sound
The strange values you measure over the cathode resistor can be cause by faulty range it must be DC voltage and current, not ac.
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Hi Helmuth,
As far as I am concerned the sound is really good. The same as it was before I had my problem with the valve and cathode resistors. I did not replace all 4 valves only the two for the left channel and I used the same Chinese EL 34 B Electron Tube. I have not run the amp for very long since the repairs but it sounds the same to me. I have acquired a set of Electro-Harmonix EL 34 tubes but I am not going to try them until I have used the amp for many more hours. I still like the MC-10L a lot and I am more familiar with its workings now.
Regards Mike.
As far as I am concerned the sound is really good. The same as it was before I had my problem with the valve and cathode resistors. I did not replace all 4 valves only the two for the left channel and I used the same Chinese EL 34 B Electron Tube. I have not run the amp for very long since the repairs but it sounds the same to me. I have acquired a set of Electro-Harmonix EL 34 tubes but I am not going to try them until I have used the amp for many more hours. I still like the MC-10L a lot and I am more familiar with its workings now.
Regards Mike.
Hi Mike, thought I would give this thread a twirl in the hope your MC10-L is still working fine. Also it is a reminder for you to check R6 to make sure that it cannot short to chassis, as explained on pages 27-28 in my guide,(now updated a little) at
http://homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.pdf
This so far un-proven yet potential problem would affect V3 mostly.
Was this the area where you had the original fault or was it around V1?
Regards
Les
http://homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.pdf
This so far un-proven yet potential problem would affect V3 mostly.
Was this the area where you had the original fault or was it around V1?
Regards
Les
Les,
Good to hear from you. Looks like you have been busy updating your very valuable information of the Yaqin MC 10 L models. It is very much appreciated. I have not had any problems with my amp since you helped me track down the problem with the shorting in the selection switch. I have probably only run up some 40 + hours since then but everything is OK (touch wood). My original problem was actually with valve 1 going ballistic. While I had the amp apart during that time I was careful to check that nothing was coming into contact with metal as there was not much room in a few places and I thought about shorting.
As I said the amp is again performing beautifully and after a few more hours use I am going to replace the original Electron Tube valves with a set of Electro-Harmonics EL-34 to see what difference it makes.
Regards, Mike.
Good to hear from you. Looks like you have been busy updating your very valuable information of the Yaqin MC 10 L models. It is very much appreciated. I have not had any problems with my amp since you helped me track down the problem with the shorting in the selection switch. I have probably only run up some 40 + hours since then but everything is OK (touch wood). My original problem was actually with valve 1 going ballistic. While I had the amp apart during that time I was careful to check that nothing was coming into contact with metal as there was not much room in a few places and I thought about shorting.
As I said the amp is again performing beautifully and after a few more hours use I am going to replace the original Electron Tube valves with a set of Electro-Harmonics EL-34 to see what difference it makes.
Regards, Mike.
Hello All,
I also had the problem with the Yaqin MC-10L output stage with the original EL34-B (made in China; Electron Tubes) valves and their 10 Ohm cathode resistors only in the right channel, i.e. after one week of playing fine, suddenly a crackling noise in the loudspeaker and then the particular resistor increased its resistance, sometimes also the fuse blown.
Same thing happened again after replacing the resistor. The first thing which I tried was to replace the bias-potis, since somebody gave me this hint, but it didn't help. The next thing, which I would like to try, is to add the (approximately) 750 Ohm resistors "Screen Grid Stoppers/Current Limiters" to the EL34. I think this time I will also replace the EL34 as well. And later I will set the bias to "only" 260mV.
Anyway, if somebody does have something to add, I will appreciate it.
Best Regards
Ralf
I don't mean to be outta line here, and I haven't read the rest of the thread, but if I was having trouble with anything with a Chinese tube I'd look at the tube first.
I've had so many problems with Chinese tubes in the past that if I was to ever own/build/repair or mod another piece of tube equipment I would never consider a Chinese made tube.
From crackling to flashing to shorts and spectacular red hot plates the Chinese tubes I played with, mostly from '95-'02 were not worth a damn.
My $.02.
Hello Hags,
thanks for Your input. Yes, I think You are correct. I also have a lot of concerns in the quality of these tubes. Basically these Chinese tubes should have at least a date code to be able to track any manufacturing problem, but they don't.
The only reason why I tried other things is to save some money for buying new tubes. But I think I have to spend it now.
Best Regards
Ralf
Hello,
now I am using tubes from Electro Harmonix and I like the sound very much.
By the way I built in a volume potentiometer (Marantz spare part) with center tap, to have a loudness poti with the appropriate caps connected to it. I did this for two reasons:
1) I have my appartement in the roof of the house, and for some reason the mid and high tone range is reflected from the 45° angle walls, or in other words I miss some bass, although the loudspeakers (Visaton Solitude) are ok.
2) I hear the music with low volume in most cases.
I like the loudness correction and I don't want to miss it now.
Best Regards
Ralf
now I am using tubes from Electro Harmonix and I like the sound very much.
By the way I built in a volume potentiometer (Marantz spare part) with center tap, to have a loudness poti with the appropriate caps connected to it. I did this for two reasons:
1) I have my appartement in the roof of the house, and for some reason the mid and high tone range is reflected from the 45° angle walls, or in other words I miss some bass, although the loudspeakers (Visaton Solitude) are ok.
2) I hear the music with low volume in most cases.
I like the loudness correction and I don't want to miss it now.
Best Regards
Ralf
Hi I also have a MC10L with a slightly different problem, I changed the Chinese tubes for Svettlana EL34 from Karltone (matched set of 4), the bias voltage was way high after i turned it on for the first time with the new tubes and there was a slight smell of buring, still i turned to bias voltage down to 400mv. All has been fine for a few month but now there is no voltage across the bias adjustment for V1 and V4.
Any idea's where I start before putting the chinese tubes back in. Top off show no sign of burn resistors etc
Thanks
Bob
Any idea's where I start before putting the chinese tubes back in. Top off show no sign of burn resistors etc
Thanks
Bob
For those with MC10L or T, I have added a cold test routine (Pages 26 to 40) to the original document that I put together. You can verify most resistances and check out the primary windings of the output transformers without removing any covers! Try that with solid state gear!
Two links (hope they work) giving the choice of PDF or WORD document.
Just copy the one you want and paste it into the address bar of your browser.
homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.doc
homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.pdf
Two links (hope they work) giving the choice of PDF or WORD document.
Just copy the one you want and paste it into the address bar of your browser.
homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.doc
homepage.ntlworld.com/lez/YAQIN MC10/A LOOK AT THE YAQIN MC10L.pdf
adding a subwoofer output to the Yaqin Amp
I thought about adding a subwoofer output to the Yaqin Amp. This is because although I have appropriate loudspeakers, the acoustic in my living room is not adequate. My appartment is under the roof of the house, and the middle and high frequencies are reflected from the walls, so the bass is a little bit weaker.
I thought the best would be to connect two resistors together to the sub-amp output for an active subwoofer, while the other ends go to the volume poti. Any other proposal?
Best Regards
Ralf
I thought about adding a subwoofer output to the Yaqin Amp. This is because although I have appropriate loudspeakers, the acoustic in my living room is not adequate. My appartment is under the roof of the house, and the middle and high frequencies are reflected from the walls, so the bass is a little bit weaker.
I thought the best would be to connect two resistors together to the sub-amp output for an active subwoofer, while the other ends go to the volume poti. Any other proposal?
Best Regards
Ralf
Biaspotentiometers
I have also a Yagin MC-10L , bought 3 years ago . Haven´t used it until now
and are now doing some upgrades . Asked myself : what happens if the wiper
on one of the biaspots loose contact ? Perhaps uncontrolled high current through that related EL 34 !? So I added a 180 K metalfilmresistor between the wiper and the leg connected to the biassupply ! The guitarampguru , Kevin
O´Connor shows this in one of his books . This mod slows down the potreaction a little and gives the EL 34 grid (5) full bias and chokes the tube ..... if the wiper
should lift ..... loose contact . To me these pots seem tiny and perhaps another
mod would be to change all four of them to a little larger cermet-type.
I´m trying to add a 750 ohm , 3W , screenresistor to each powertube . But
if possible without taking everything apart ...... Can I cut the ultralinear screencables at the side of the outputtransformer and solder in the resistors
there ? ( with some shrinkisolation at the ends ? ) Or must these resistors be
close to the pin 4 at each socket ? Thanks for some answers . Steven
I have also a Yagin MC-10L , bought 3 years ago . Haven´t used it until now
and are now doing some upgrades . Asked myself : what happens if the wiper
on one of the biaspots loose contact ? Perhaps uncontrolled high current through that related EL 34 !? So I added a 180 K metalfilmresistor between the wiper and the leg connected to the biassupply ! The guitarampguru , Kevin
O´Connor shows this in one of his books . This mod slows down the potreaction a little and gives the EL 34 grid (5) full bias and chokes the tube ..... if the wiper
should lift ..... loose contact . To me these pots seem tiny and perhaps another
mod would be to change all four of them to a little larger cermet-type.
I´m trying to add a 750 ohm , 3W , screenresistor to each powertube . But
if possible without taking everything apart ...... Can I cut the ultralinear screencables at the side of the outputtransformer and solder in the resistors
there ? ( with some shrinkisolation at the ends ? ) Or must these resistors be
close to the pin 4 at each socket ? Thanks for some answers . Steven
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