Comments for Yaqin Tube Valve Amplifiers http://yaqin.slickpepper.org.uk A site dedicated to affordably priced yet high quality Yaqin tube audio equipment Wed, 28 Jul 2010 17:43:18 +0000 http://wordpress.org/?v=2.9.2 hourly 1 Comment on MC-10L by Alun http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-698 Alun Wed, 28 Jul 2010 17:43:18 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-698 I've just got MC-10L and it's grrrrreat !!! The top valve (with the gate strapped to the lower anode) is correct, it's effectively a high impedance constant current source for the incoming anode (as long as there's PSU headroom), have used this myself a few times, so the actual stage should be treated as cascode, but with an anode C-I feed. the 1M res & 220nF cap then serve as both a bias corrector and a LF rolloff stage to the phase splitting long-tail pair. Think the circuits right, but I would have included a grid-stopper in the upper triode's gate. Hope this helps Alun I’ve just got MC-10L and it’s grrrrreat !!!
The top valve (with the gate strapped to the lower anode) is correct, it’s effectively a high impedance constant current source for the incoming anode (as long as there’s PSU headroom), have used this myself a few times, so the actual stage should be treated as cascode, but with an anode C-I feed. the 1M res & 220nF cap then serve as both a bias corrector and a LF rolloff stage to the phase splitting long-tail pair.

Think the circuits right, but I would have included a grid-stopper in the upper triode’s gate.

Hope this helps

Alun

]]> Comment on MC-100B by cesar amadeus http://yaqin.slickpepper.org.uk/amplifiers/yaqin-mc-100b/comment-page-1#comment-695 cesar amadeus Tue, 27 Jul 2010 11:40:39 +0000 http://yaqin.slickpepper.org.uk/?page_id=146#comment-695 hello l live in china canton REN MIN NORTH ROAD 917, DONG BAO BUILDING ROOM 819 GUANGZHOU CHINA TELEPHONE 86223173 and l want to buy this unit where is your shop in guangzhou please hello
l live in china canton
REN MIN NORTH ROAD 917, DONG BAO BUILDING ROOM 819 GUANGZHOU CHINA TELEPHONE 86223173

and l want to buy this unit

where is your shop in guangzhou please

]]> Comment on MC-10L by Ian http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-693 Ian Mon, 26 Jul 2010 15:13:59 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-693 Interesting post by Jon Chia, I'm in nearly the same position. I have even ordered those same valves and am waiting on the amp, I'm looking forward to playing with this amp :D Has anyone run one of these amps in a triode strapped configuration? Cheers Ian Interesting post by Jon Chia, I’m in nearly the same position. I have even ordered those same valves and am waiting on the amp, I’m looking forward to playing with this amp :D
Has anyone run one of these amps in a triode strapped configuration?
Cheers
Ian

]]> Comment on MC-10L by john http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-687 john Sun, 25 Jul 2010 15:01:01 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-687 Thanks Les, I see as well the top grid is going to the bottom plate (anode) directly. I would have to see an actual amp and do testing. I do not think this schematic is drawn correctly and wonder what else the company wants to play games with. Is there other bugaboos? I know in Hong Kong they play "gotcha" often as a revenge scheme. Thanks Les, I see as well the top grid is going to the bottom plate (anode) directly. I would have to see an actual amp and do testing. I do not think this schematic is drawn correctly and wonder what else the company wants to play games with. Is there other bugaboos? I know in Hong Kong they play “gotcha” often as a revenge scheme.

]]> Comment on MC-10L by Jon Chia http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-685 Jon Chia Sun, 25 Jul 2010 10:43:17 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-685 Hi, After reading this forum, I have gained enough confidence in buying the MC10-L. Have placed order and it should be here 2 to 3 weeks time. Never own a tube amp but you guys helped in my decision making. Question: About adjusting the bias, the amp should be switched on and speakers loaded, right? I intend to order some backup tubes. Here's what I have in mind: 6N1P-EV (for Pre) 6P3S-E (for Power) Any comments or suggestions are most welcome. Thanks for reading! Jon Hi,
After reading this forum, I have gained enough confidence in buying the MC10-L. Have placed order and it should be here 2 to 3 weeks time. Never own a tube amp but you guys helped in my decision making.

Question:
About adjusting the bias, the amp should be switched on and speakers loaded, right?

I intend to order some backup tubes. Here’s what I have in mind:
6N1P-EV (for Pre)
6P3S-E (for Power)

Any comments or suggestions are most welcome.

Thanks for reading!

Jon

]]> Comment on MC-10L by Les http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-684 Les Sun, 25 Jul 2010 08:15:05 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-684 Hi John, I wonder if you have the schematic drawn by Yaqin on graph paper as there is indeed a missing HT connection between B+ and the 33k resistor feeding the upper valve. The Anode of this valve should be around 300V and the cathode will be about 124V. There should be about 3V drop across the 1k resistor to give 121V on the anode of the lower valve. Cheers, Les Hi John, I wonder if you have the schematic drawn by Yaqin on graph paper as there is indeed a missing HT connection between B+ and the 33k resistor feeding the upper valve. The Anode of this valve should be around 300V and the cathode will be about 124V. There should be about 3V drop across the 1k resistor to give 121V on the anode of the lower valve.
Cheers, Les

]]> Comment on MC-10L by john http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-683 john Sat, 24 Jul 2010 23:52:13 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-683 thanks Les for the explanation. I still see the schematic has no B+ shown for the plates in first amp. What is the voltage supposed to be? thanks Les for the explanation. I still see the schematic has no B+ shown for the plates in first amp. What is the voltage supposed to be?

]]> Comment on MC-10L by Les http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-681 Les Sat, 24 Jul 2010 22:38:10 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-681 Wish I could help Harry but so far I have not found a replacement. I thought the Yaqin used an Alps control but I have a feeling it is a copy due to the fact that it has a splined (knurled) shaft and I am certain Alps only made straight shaft potentiometers. The actual shaft length from the threaded boss appears to be about 20mm and a replacement has to be the same in order to fit the knob correctly. You may be able to find a dual control of a more conventional open style of manufacture from a supplier. I for one will keep looking as I think it may be a component that I myself may wish to replace in my Yaqin, which incidentally is the same early type as yours. The 20k value is not too critical and a 50k or even a 100k could be used, the control feeds the grid of the first valve which already has a 100k resistor on it. As stated in my earlier posts, I use a remote controlled motorised Alps control for my volume control so the Yaqin control is normally left fully on. I think that if I was in a position where I desperately needed a replacement, it might be possible to fit an Alps control and extend its normal 11mm shaft with a coupler and make up the remaining 9mm using part of the old control. This would give me the splined interface back but careful measurement needs to be made first to ensure the process is completely viable. Also, don't give up on the chance of perhaps getting a control from China and of course, keep a good eye on popular auction sites for a possible replacement. Les Wish I could help Harry but so far I have not found a replacement. I thought the Yaqin used an Alps control but I have a feeling it is a copy due to the fact that it has a splined (knurled) shaft and I am certain Alps only made straight shaft potentiometers. The actual shaft length from the threaded boss appears to be about 20mm and a replacement has to be the same in order to fit the knob correctly. You may be able to find a dual control of a more conventional open style of manufacture from a supplier. I for one will keep looking as I think it may be a component that I myself may wish to replace in my Yaqin, which incidentally is the same early type as yours. The 20k value is not too critical and a 50k or even a 100k could be used, the control feeds the grid of the first valve which already has a 100k resistor on it. As stated in my earlier posts, I use a remote controlled motorised Alps control for my volume control so the Yaqin control is normally left fully on.
I think that if I was in a position where I desperately needed a replacement, it might be possible to fit an Alps control and extend its normal 11mm shaft with a coupler and make up the remaining 9mm using part of the old control. This would give me the splined interface back but careful measurement needs to be made first to ensure the process is completely viable. Also, don’t give up on the chance of perhaps getting a control from China and of course, keep a good eye on popular auction sites for a possible replacement.
Les

]]> Comment on MC-10L by Harry http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-680 Harry Sat, 24 Jul 2010 12:23:12 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-680 Hi Les, Any suggestions for replacing the volume pot on the MC10L? Mine developed scratchy noises in the left channel. Opening the cover revealed a sealed pot so I could not spray electronics cleaner into it. The schematic indicates a 20K unit but most attenuators I could find are either 10K, 25K, 50K, 100K, 250K. I have the older version without the access holes and the capacitors sticking up through the top cover. Many thanks! Hi Les,

Any suggestions for replacing the volume pot on the MC10L? Mine developed scratchy noises in the left channel. Opening the cover revealed a sealed pot so I could not spray electronics cleaner into it. The schematic indicates a 20K unit but most attenuators I could find are either 10K, 25K, 50K, 100K, 250K.

I have the older version without the access holes and the capacitors sticking up through the top cover.

Many thanks!

]]> Comment on MC-10L by Les http://yaqin.slickpepper.org.uk/amplifiers/mc-10l/comment-page-3#comment-679 Les Sat, 24 Jul 2010 10:58:53 +0000 http://yaqin.slickpepper.org.uk/?page_id=5#comment-679 The first half of V1 consists of a voltage amplifier using its second half as a kind of infinite anode load (but by voltage values approximately 40k Ohms) with the overall current set by R104. This is approximately 3.5mA and biases the top halves grid at minus 3.5V with respect to its cathode. The circuit allows direct connection of the second valve V2, without any capacitor which could otherwise produce unwanted phase shifts. It also improves the low frequency stability when feedback is applied to R103 via C106 and R117. The intermediate stage consists of a cathode-coupled phase-splitter often called a Schmitt phase splitter and provides a push-pull drive voltage for the output stage. It is necessary in a cathode-coupled phase splitter for the anode load of one side to be slightly higher than the other if reasonable balance is to be obtained thus one is at 51k and the other 47k. At low frequencies, the presence of C103 and R106 in the grid circuit of the right hand triode produces both phase and amplitude unbalance. The frequency at which the lack of balance becomes significant depends on the time constant of these components and in the MC10L it is less than 5Hz. The cathode voltage on the upper section of the first 6N1 (V1 Pin 3) determines the operating conditions of the phase splitter. The power dissipation in the 30k cathode resistor ((127V x 127V) / 30000) is approximately half a Watt and being fairly constant I guess Yaqin decided to fit a 2W component for long term reliability. Hope this helps, Les The first half of V1 consists of a voltage amplifier using its second half as a kind of infinite anode load (but by voltage values approximately 40k Ohms) with the overall current set by R104. This is approximately 3.5mA and biases the top halves grid at minus 3.5V with respect to its cathode. The circuit allows direct connection of the second valve V2, without any capacitor which could otherwise produce unwanted phase shifts. It also improves the low frequency stability when feedback is applied to R103 via C106 and R117.
The intermediate stage consists of a cathode-coupled phase-splitter often called a Schmitt phase splitter and provides a push-pull drive voltage for the output stage. It is necessary in a cathode-coupled phase splitter for the anode load of one side to be slightly higher than the other if reasonable balance is to be obtained thus one is at 51k and the other 47k. At low frequencies, the presence of C103 and R106 in the grid circuit of the right hand triode produces both phase and amplitude unbalance. The frequency at which the lack of balance becomes significant depends on the time constant of these components and in the MC10L it is less than 5Hz. The cathode voltage on the upper section of the first 6N1 (V1 Pin 3) determines the operating conditions of the phase splitter. The power dissipation in the 30k cathode resistor ((127V x 127V) / 30000) is approximately half a Watt and being fairly constant I guess Yaqin decided to fit a 2W component for long term reliability.
Hope this helps, Les

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