Just a little update.
I got a very noticeable improvement in sound by by-passing the three circuit boards in the in-put path. By adding inputs next to the volume pot (see first pic), it also by-passed the selector switch so now only has one set of in-puts, but worth it to me.
The second pic shows the amp rebuilt using only the transformers and a few little bits like the volume pot, the circuit is off a friend that is a speaker/valve amp designer, he also wired up the new circuit point to point for me.
Gave the 6P3S-E's to a guitarist friend who loves them in his hybrid guitar amp , too rolled off down bottom in the new amp build, I found the Svetlana winged C EL34s to be best so far.
Sound is very, very much improved now.
Oh! near forgot, the O'rings on the valves cleaned the sound up a lot too, especially on the Russian 6N1P's, noisy little buggers as it turns out
I got a very noticeable improvement in sound by by-passing the three circuit boards in the in-put path. By adding inputs next to the volume pot (see first pic), it also by-passed the selector switch so now only has one set of in-puts, but worth it to me.
The second pic shows the amp rebuilt using only the transformers and a few little bits like the volume pot, the circuit is off a friend that is a speaker/valve amp designer, he also wired up the new circuit point to point for me.
Gave the 6P3S-E's to a guitarist friend who loves them in his hybrid guitar amp , too rolled off down bottom in the new amp build, I found the Svetlana winged C EL34s to be best so far.
Sound is very, very much improved now.
Oh! near forgot, the O'rings on the valves cleaned the sound up a lot too, especially on the Russian 6N1P's, noisy little buggers as it turns out
Attachments
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Guys, this is not a buffer. It is a common cathode gain stage. So it has gain you probably do not need.
Quite correct costis_n, it would be difficult to make a cathode follower with those tubes yet strange the makers of the kit call it a buffer and then later they change its title to a pre-amplifier albeit with a gain of 3! To Data, I have long held suspicions about the input wiring of the MC-10L with all of its four input lines bunched together in just one screened cable. The idea might have some level of success if the impedance was very much lower even though I would still have certain reservations. For me, individual screened leads would be the way to go, just to get over the awful cross talk one gets with the present set-up. Using an external switch box, built to prevent cross talk, I only need one channel input. Next time I do the annual check over of the amps internals, I may hard wire just one set of RCA's direct to the volume control with separate screened leads. But what about the redundant front panel switch? Perhaps this could be used to direct the four output tube cathode current monitors to a dedicated socket on the rear of the amp. It would thus become a means of quickly checking the tube currents at any time..just a thought! Les
yet strange the makers of the kit call it a buffer and then later they change its title to a pre-amplifier albeit with a gain of 3! To Data, I have long held suspicions about the input wiring of the MC-10L with all of its four input lines bunched together in just one screened cable. The idea might have some level of success if the impedance was very much lower even though I would still have certain reservations. For me, individual screened leads would be the way to go, just to get over the awful cross talk one gets with the present set-up. Using an external switch box, built to prevent cross talk, I only need one channel input. Next time I do the annual check over of the amps internals, I may hard wire just one set of RCA's direct to the volume control with separate screened leads. But what about the redundant front panel switch? Perhaps this could be used to direct the four output tube cathode current monitors to a dedicated socket on the rear of the amp. It would thus become a means of quickly checking the tube currents at any time..just a thought! LesQuite correct costis_n, it would be difficult to make a cathode follower with those tubes
It would be easy, really, just rearrange the load and provide for biasing.
XiangSheng 728
Ronny, have you tried the 728A? I am keen on buying a preamp and hesitate between 728A, 708B and Little Dot MK3.
The problem with the 728A is that there is very title info for mod online...
Serge
Ronny, have you tried the 728A? I am keen on buying a preamp and hesitate between 728A, 708B and Little Dot MK3.
The problem with the 728A is that there is very title info for mod online...
Serge
There are a couple of different versions of the 728a and some have already been enhanced having better caps and perhaps other components. Be careful to check the photos carefully. From memory the better caps are black and bigger than the stock ones. There also significant differences in the PCB layouts between the 2 variants plus differences in colours of the panels and art work...
I have the same amp.
I replaced the preamp tubes with some NOS Russian military and the bass response was like night and day. The amp sounds much more powerful due to fuller bass. The amp sounds fantastic now. I have had mine for a year and a half with no issues.
Didn't notice any change with a power tube swap but I thought it was a good idea for reliability.
Matt
I replaced the preamp tubes with some NOS Russian military and the bass response was like night and day. The amp sounds much more powerful due to fuller bass. The amp sounds fantastic now. I have had mine for a year and a half with no issues.
Didn't notice any change with a power tube swap but I thought it was a good idea for reliability.
Matt
After reading all the good things about this amp, I just had to try one. It is on its way.
I also ordered the Russian military NOS 6N1P tubes and have 0.1uf 630v Russian K42Y-2 and .22 uF ready to go in for coupling caps.
Thanks to Hi-Q for the Word mods document, I plan to add to it. I am considering the grid resistors mod with the electrolytic bypass, Class X, and Y caps on the mains, a new Alps pot perhaps with a new Elma selector switch, etc. Hope to update with photos.
The one pictured is the one coming with the chrome top.
Any mod ideas welcomed.
Attachments
The transformers are not potted in oil. But they can run quit hot so wax will melt a little.
Some more to read,
https://www.diyaudio.com/community/threads/yaqin-mc10l.110483/
Some more to read,
https://www.diyaudio.com/community/threads/yaqin-mc10l.110483/
Did you use a Variac or a Bulb limiter to slowly power up the amplifier?
I had an old used Hallicrafters short wave radio. It played for hundreds of hours; then the power transformer shorted and leaked out lots of wax.
A new power transformer fixed the problem.
Electrolytic capacitors sometimes short or have excessive leakage current.
Output tubes short.
Lots of things can cause a power transformer to go bad.
Did you purchase a non working used amplifier?
Were you able to power up the amplifier?
Does it work?
Does it sound OK?
It might be easier and quicker to do some simple tests on the amplifier and to do a careful visual inspection;
instead of reading 407 entries on the MC-1010 thread link in Post # 77 above.
As always, get an amplfier Working Properly before modifying it.
I had an old used Hallicrafters short wave radio. It played for hundreds of hours; then the power transformer shorted and leaked out lots of wax.
A new power transformer fixed the problem.
Electrolytic capacitors sometimes short or have excessive leakage current.
Output tubes short.
Lots of things can cause a power transformer to go bad.
Did you purchase a non working used amplifier?
Were you able to power up the amplifier?
Does it work?
Does it sound OK?
It might be easier and quicker to do some simple tests on the amplifier and to do a careful visual inspection;
instead of reading 407 entries on the MC-1010 thread link in Post # 77 above.
As always, get an amplfier Working Properly before modifying it.
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It has been a long time since I wrote my original guide to the MC10L, I had an early one too with no accessible bias monitor or adjustment points.
It is a pain to have to remove the top plate every time you want to set this up or monitor the output tubes. Yaqin did so many changes right up to the MC13S but I tried to keep up though there are possibly some much later changes I do not know about. I could give you the link to my website where my document is but some sites have banned me for doing this. I really do not know why as it was best to do this, such that the latest version was always available and I do not run a business, just a hobby where I try to help. Saddest loss was being banned from Vinyl Engine because I suspect they did not like my website link about the Yaqin MS22, but it was the most sensible thing to do as it was changed so much later. It hurts when this happens as owners of these sites do not appreciate you are only doing the very best to help their readers with the latest updated information.
It is a pain to have to remove the top plate every time you want to set this up or monitor the output tubes. Yaqin did so many changes right up to the MC13S but I tried to keep up though there are possibly some much later changes I do not know about. I could give you the link to my website where my document is but some sites have banned me for doing this. I really do not know why as it was best to do this, such that the latest version was always available and I do not run a business, just a hobby where I try to help. Saddest loss was being banned from Vinyl Engine because I suspect they did not like my website link about the Yaqin MS22, but it was the most sensible thing to do as it was changed so much later. It hurts when this happens as owners of these sites do not appreciate you are only doing the very best to help their readers with the latest updated information.
Hey folks, thanks for the responses. The Amplifier was purchased working, and is working still. I went to bias it yesterday and I notices, what is the wax I guess Mostly on the right side of the power transformer. It is an old model with the biasing having to be done inside. The left and right channel bias is set pretty far off right now 4V and 2V, but I will be working on fixing that next. I have been thinking abot some new tubes for it, as I do not know the history on the tubes, but it looks like sovtek power tubes. They had been removed and not reinstalled into thier correct places. So I am guessing that is why the bias voltage may be off left and right. I'll get a picture posted tomorrow. Would posting in the other thread be more appropriate? Thanks all.