Ok - you need to know what the output of your phono stage is presenting to the amp. The RCA plugs on the front are for a signal of .6 mV. That would be good for a "typical" pre out from a preamp. If you are using some other signal from something other than a preamp you need to know EXACTLY what the output is. This amp is set up to look for a LINE level input - should be pretty straight forward. You may need to adjust the volume more for a phono than aux but that is really dependent on your pre amp (and phono cartridge).
Basically you use the front inputs IF you are using a pre amp and the back RCA inputs are used when you don't have a preamp (and no phono). IF you have a phono input you need a pre amp and can hook the output of the preamp to the front (.6mV input) of the amp. You should be good.
There's a few ways to blow up something. Changing the voltage setting on the front of the amp with the amp ON AND volume up is the one thing the owners manual warns you not to do and the other which is not in the owners manual; turning the amp off then right back on - bad with all tube amps IMHO and specially with this one.
Oh and there are soldering issues with mine when I got it. I'm still wondering why I didn't send it back after 2 weeks and a channel drop.
USA built is better and less expensive. Gonna have to stand on that even tho I have one of these amps as a daily driver.
If you are looking for better bass and all is well. There's a suggestion in this thread (I think) to use a variac, lower the input voltage to like 104 AC and up the bias to the KT88 to a comfortable 70 mV (verify that). I've got good tight bass with this change and I listen to this amp 8 hrs a day (after a re-solder of ALL joints). It's been a long while since I hooked up the variac... 8 months or so, daily drive; KT88s are all good (knock knock). I kept the Stock KT-88s and changed out the 12AX7 and 6SN7 tubes to nothing exotic and this amp sounds alright.. Again crappy build quality (solder) IMHO.
Cheers,
Bob
Thanks, Bob. And others.
Please, anyone, take a look at this schematic (attached here for your convenience). It looks to me as though the ".2V" circuit and the ".6V" circuit are not different. It looks to me as though they both go directly through the same toggle switch. So......there should be no different, right? There is no special circuitry that is unique to either one of these modes (.2V and .6V), other than the conductor that runs from the RCA jack(s) to the toggle switch.
Again, my amp fried some circuitry (between the printed circuit board at the top of the amp chassis, making repair difficult and costly) when I plugged a phono preamp into the front plugs, and had the toggle switch on ".6V". I had plugged the preamp to these inputs, with the preamp on, had the toggle already turned to ".6V" and the volume turned all the way down when I turned the amp on. It fried immediately, as evidenced by some loud high-voltage snapping near Kt-88 #3. There was no smoke and no smell. Apparently, the tech, who doesn't speak English very well, did not enjoy this repair experience. He said the problem was in one channel. Then, later, he said the problem had to do with the front inputs. The shop that sent it to the tech warns me not to use the front inputs. I am not a cranky guy, but this "don't use the circuit we repaired" business is **. IMHO. But again, it appears that getting useful information from the tech or the shop is difficult or impossible. I may need to disassemble something and make a verification that these front inputs are wired properly.
When it says ".6V" on this front input, does this mean there is a .6V signal coming into these two RCA inputs? This .6V signal does not change with volume or music signal? Like a "carrier" voltage? How would I measure this voltage? Between the two hots and two neutrals on the RCA plug? Or between the two hots? Talk to me.
Please, anyone, take a look at this schematic (attached here for your convenience). It looks to me as though the ".2V" circuit and the ".6V" circuit are not different. It looks to me as though they both go directly through the same toggle switch. So......there should be no different, right? There is no special circuitry that is unique to either one of these modes (.2V and .6V), other than the conductor that runs from the RCA jack(s) to the toggle switch.
Again, my amp fried some circuitry (between the printed circuit board at the top of the amp chassis, making repair difficult and costly) when I plugged a phono preamp into the front plugs, and had the toggle switch on ".6V". I had plugged the preamp to these inputs, with the preamp on, had the toggle already turned to ".6V" and the volume turned all the way down when I turned the amp on. It fried immediately, as evidenced by some loud high-voltage snapping near Kt-88 #3. There was no smoke and no smell. Apparently, the tech, who doesn't speak English very well, did not enjoy this repair experience. He said the problem was in one channel. Then, later, he said the problem had to do with the front inputs. The shop that sent it to the tech warns me not to use the front inputs. I am not a cranky guy, but this "don't use the circuit we repaired" business is **. IMHO. But again, it appears that getting useful information from the tech or the shop is difficult or impossible. I may need to disassemble something and make a verification that these front inputs are wired properly.
When it says ".6V" on this front input, does this mean there is a .6V signal coming into these two RCA inputs? This .6V signal does not change with volume or music signal? Like a "carrier" voltage? How would I measure this voltage? Between the two hots and two neutrals on the RCA plug? Or between the two hots? Talk to me.
First may I say from a personal point of view that I do not for one moment believe the damage in the output stage was caused in any way by an incorrect input. If anything your speakers would have lost their cones, the fact that the amp blew on one channel is indicative of something else being wrong. For my money I would hazard a guess that one of the tubes flashed over internally, cannot be trusted and should be replaced. With regard to the different RCA jacks, indeed there is no magic attenuator acting directly on the signal you are feeding in. One half of the switch merely gives you an extra set of inputs that are set aside from the rest. The magic comes with the other half of the switch (circled in Red on the attachment) which adjusts the gain of the input stage. I assume it is arranged such that the signal sent onward into the amp, after the input stage, will be of similar amplitude with 0.2V being fed into one of the 4 input RCA's or alternative 0.6V fed into the dedicated pair selected by the switch.
Attachments
Oops. I guess I failed to post the schematic. Thanks, Hi-Q.
I see the red circle. But......isn't everything downstream from the toggle switch treated the same? It looks to me like the signal from the input switch and the signal from the (".6V") front input both go directly to the toggle switch. Therefore, this amp does not treat any input different from any other input. Am I wrong? Does the red circled area process a signal from only one input source? If the answer is yes, I am going to wonder how it does that.
I see the red circle. But......isn't everything downstream from the toggle switch treated the same? It looks to me like the signal from the input switch and the signal from the (".6V") front input both go directly to the toggle switch. Therefore, this amp does not treat any input different from any other input. Am I wrong? Does the red circled area process a signal from only one input source? If the answer is yes, I am going to wonder how it does that.
I've had mine apart and this is what I've found. Just looks like a different set of resistors with the toggle switch.
My bet your problem was a bad solder joint. I'd look at that output tube socket you got a flash from and look CLOSELY at the solder joints.
Cheers,
Bob
Ah hah! I see. So.....would this probably mean that input sensitivity is reduced when the switch is turned from ".2V" to ".6V" inputs? So.....with the switch on ".6V" the input signal is amplified a bit less?
Yep, I did not want to get too technical 
but the amount of gain is all to do with the amount of negative feedback which is being obtained from the speaker output and fed to the cathode of the input amplifier. In the 0.6V position full feedback is being developed across the 330 Ohm resistor. When you select one of the 0.2V inputs then you need a bit more gain to compensate for the lower level, so the switch changes the resistor to approximately 100 Ohms. This has the effect of lowering the amount of negative feedback resulting in an increase in gain. Obviously you need an increase of approximately 3 times which in technical terms is an increase of approximately 9.5dBV.
but the amount of gain is all to do with the amount of negative feedback which is being obtained from the speaker output and fed to the cathode of the input amplifier. In the 0.6V position full feedback is being developed across the 330 Ohm resistor. When you select one of the 0.2V inputs then you need a bit more gain to compensate for the lower level, so the switch changes the resistor to approximately 100 Ohms. This has the effect of lowering the amount of negative feedback resulting in an increase in gain. Obviously you need an increase of approximately 3 times which in technical terms is an increase of approximately 9.5dBV.Great big thanks and one question.
Hello all,
First off, I wanted to thank all of you that have contributed to this thread. I don't think I would have had the courage to buy an amplifier from Hong Kong were it not for all this info. Many other forums dismiss these products by saying "I've never heard it, but it must be crap!" My Yaqin had been sounding wonderful for over a year now. I found that the JJ 803 long plate 12ax7 sounds wonderful in it without having to pay NOS prices, and the EH 6sn7 is quite acceptable as well.
I see there are a lot of thoughts on here about bios and voltages. A common thought seems to be that this unit sounds best when biased to between .60 and.725 volts, but it causes an adverse inpact on tube life. My questions is: What about those new KT120 tubes. Assuming the filement supply is strong enough, what would happen of you threw in a set of those and cranked the bias up to .6 to .7? Has anyone tried this? Does anyone have any theories?
Thanks again,
Jpeg
Hello all,
First off, I wanted to thank all of you that have contributed to this thread. I don't think I would have had the courage to buy an amplifier from Hong Kong were it not for all this info. Many other forums dismiss these products by saying "I've never heard it, but it must be crap!" My Yaqin had been sounding wonderful for over a year now. I found that the JJ 803 long plate 12ax7 sounds wonderful in it without having to pay NOS prices, and the EH 6sn7 is quite acceptable as well.
I see there are a lot of thoughts on here about bios and voltages. A common thought seems to be that this unit sounds best when biased to between .60 and.725 volts, but it causes an adverse inpact on tube life. My questions is: What about those new KT120 tubes. Assuming the filement supply is strong enough, what would happen of you threw in a set of those and cranked the bias up to .6 to .7? Has anyone tried this? Does anyone have any theories?
Thanks again,
Jpeg
Take care! Remember that running higher standing current does not just impact on tube life. You will be asking the mains transformer to do more work and what with the extra 1 Amp+ required on the heater windings it may cause the transformer to complain. It all depends on how much extra capacity was provided by the circuit designers and this we do not know. Common sense tells me that it will be low due to production cost trimming so bear this in mind when demanding more from the intended design. A rough guide to how the mains transformer is reacting is to measure the cold and hot resistance of the mains input. Before you use your amp for the evening, unplug the amplifier from the mains and apply the Multimeter across the pins of the mains plug, making sure of course that the mains switch on the amplifier is set to ON. Suppose it measures say 5.8 Ohms.
The Maximum allowed resistance rise = (cold resistance x 0.1965) + cold resistance, which in our example would be (5.8 x 0.1965) + 5.8 that works out as 1.1397 + 5.8 = 6.9397 Ohms.
Run the amp for the evening and re-measure the resistance when the mains transformer is hot. The answer you get using your transformers cold figure is the maximum resistance you want to see when you repeat the measurement exercise when the amplifier is hot.
The increase in the resistance reading is due to the resistance of the copper wire in the transformer rising with temperature and the formula will give you some idea if you are pushing the transformer to its thermal limits. It's only a rough guide of course but may put some minds at rest.
The Maximum allowed resistance rise = (cold resistance x 0.1965) + cold resistance, which in our example would be (5.8 x 0.1965) + 5.8 that works out as 1.1397 + 5.8 = 6.9397 Ohms.
Run the amp for the evening and re-measure the resistance when the mains transformer is hot. The answer you get using your transformers cold figure is the maximum resistance you want to see when you repeat the measurement exercise when the amplifier is hot.
The increase in the resistance reading is due to the resistance of the copper wire in the transformer rising with temperature and the formula will give you some idea if you are pushing the transformer to its thermal limits. It's only a rough guide of course but may put some minds at rest.
Tung Sol KT120
Jpeg, I've been running the Tung Sol KT120s in my Yaqin MC100b for about six months. The amp has been hard on KT88s, but the KT120s have fared better. I keep them biased around 60-65. They're warm and tubey sounding. The bass is there but looser than the kt88s. The KT120 sound better than the JJs,(unfocused, but good bass) or Genalex reissues (very colored in this amp).
If you can get a hold of some old stock tubes you might be surprised at the difference you hear:
For 6Sn7s I like original Tung Sol and Sylvanias in the MC100b. RCAs are just a little blurred but have beautiful midrange. I tried the Tung Sol reissue 6SN7, and they are barely an improvement over the stock Chinese tubes.
I tried the JJ 803s, they do have less high end (which is a good thing with this amp), but were a bit lifeless.
I've rolled a lot of tubes through my Yaqin, maybe some of my opinions/experiences above will be of some use to you.
Jpeg, I've been running the Tung Sol KT120s in my Yaqin MC100b for about six months. The amp has been hard on KT88s, but the KT120s have fared better. I keep them biased around 60-65. They're warm and tubey sounding. The bass is there but looser than the kt88s. The KT120 sound better than the JJs,(unfocused, but good bass) or Genalex reissues (very colored in this amp).
If you can get a hold of some old stock tubes you might be surprised at the difference you hear:
For 6Sn7s I like original Tung Sol and Sylvanias in the MC100b. RCAs are just a little blurred but have beautiful midrange. I tried the Tung Sol reissue 6SN7, and they are barely an improvement over the stock Chinese tubes.
I tried the JJ 803s, they do have less high end (which is a good thing with this amp), but were a bit lifeless.
I've rolled a lot of tubes through my Yaqin, maybe some of my opinions/experiences above will be of some use to you.
thanks randybrinkman for that info.
I've been curious about trying the KT120's in my 100B, think I'll pick up a set and give them a shot.
Over all I've been very happy with the 100B.
So far I've exchanged the 12ax7's with 5751's. Made a nice difference.
Exchanged the 6N8P with some really nice 6SN7's I got off a guy from ebay. Made a real nice difference.
And put in a quad of the Red Lions KT88's.
We'll see what the KT120's do.
John
I've been curious about trying the KT120's in my 100B, think I'll pick up a set and give them a shot.
Over all I've been very happy with the 100B.
So far I've exchanged the 12ax7's with 5751's. Made a nice difference.
Exchanged the 6N8P with some really nice 6SN7's I got off a guy from ebay. Made a real nice difference.
And put in a quad of the Red Lions KT88's.
We'll see what the KT120's do.
John
Well I've been running with the KT120's for a couple of days and so far so good.
Running them in the .60 -.62 range like randybrinkman.
They do have a different sound form the KT88's and I'm liking it.
Think I'll stick with them for a while and see how they work for the long term.
I got the Matched Quad from a guy on the bay for $170.00.
John
Running them in the .60 -.62 range like randybrinkman.
They do have a different sound form the KT88's and I'm liking it.
Think I'll stick with them for a while and see how they work for the long term.
I got the Matched Quad from a guy on the bay for $170.00.
John
Keep us posted
Thanks for the info, let us know how long they last. I ended up going with a set of Shuguang Treasures which are on thier way from China as we speak. The first thing I did when I got my Yaqin was replace the 6sn7's with a set of used Sylvania chrome tops, and they sounded very good for a month or so, then one channel got really low. I picked up 4 or 5 more at a hamfest, but I just couldn't get it to sound good again. I saw in a forum somewhere that the EH 6sn7's sounded a lot like the Sylvanias, so I bought them and indeed they do. I ran mine with the JJ 803's, the EH 6sn7's and the Gold Lion KT88s for about a year and I was quite pleased. Alas, I think one of my Gold Lions is gassy.
I will let you know how the treasures sound in the Yaqin once the get here and I get them burned in.
Thanks for the info, let us know how long they last. I ended up going with a set of Shuguang Treasures which are on thier way from China as we speak. The first thing I did when I got my Yaqin was replace the 6sn7's with a set of used Sylvania chrome tops, and they sounded very good for a month or so, then one channel got really low. I picked up 4 or 5 more at a hamfest, but I just couldn't get it to sound good again. I saw in a forum somewhere that the EH 6sn7's sounded a lot like the Sylvanias, so I bought them and indeed they do. I ran mine with the JJ 803's, the EH 6sn7's and the Gold Lion KT88s for about a year and I was quite pleased. Alas, I think one of my Gold Lions is gassy.
I will let you know how the treasures sound in the Yaqin once the get here and I get them burned in.
I just put one of these amps on layaway at the stereo shop. I made the mistake of switching the pre- input on the front while it was turned on. It did pop when I did that. Hopefully no damage was done.
Im getting some Gold Lion KT88 tubes from the store. I am also looking at the smaller tubes to see what to go with. Aer the Gold Lion 12AX7 tubes worth checking out? Also I see someone suggested Sylvania for the 6SN7 tubes.
Also what is suggested to best cover the caps on this amp so as to not get a lethal dose of electricity if touched?
Im getting some Gold Lion KT88 tubes from the store. I am also looking at the smaller tubes to see what to go with. Aer the Gold Lion 12AX7 tubes worth checking out? Also I see someone suggested Sylvania for the 6SN7 tubes.
Also what is suggested to best cover the caps on this amp so as to not get a lethal dose of electricity if touched?
It's worth measuring your amp to see whether it has this problem as I believe the issue was fixed on later amps. If yours is dangerous, electrical tape is a cheap, easy and effective way of covering up. If you want something more attractive, a lacquer will also solve solve the problem.
Personally, i've ordered a set of 4 of these caps to replace the dangerous ones on my amp. I'll try to remember to post once they arrive and let you know how the install goes. These are 820uf rather than the standard 470uf Yaqin fitted so I hope to see some improvement.
Randy- how are the KT 120s holding up in your 100B? I have been told the power transformers in this amp aren't the best. They run hot even with KT88 tubes, so using KT 120s might be a stretch for longevity. The KT 88 tubes use 1.65 volts, where as the KT 120s use 1.9 volts. The power transformers may not be up to this over the long haul.
I'm interested in acquiring a Yaqin MC-100B. I've been doing quite of research the last couple of days and it has brought me here. The 100B seems to be quite popular and some very knowledgeable folks have taken to modding it. I plan to build a low-power valve system around a set of Spica TC-50s or 60s(known for their tonal balance and imaging qualities) or a set of small Polk SDAs. Although I'm leaning toward the Spica, they're hard to find in good condition and unmodified. So, I'll probably end up with the Polks.
I found the Canadian Supplier that has warranty coverage and does some on-site adjustments in his shop, and I'll pull the trigger on this sale in the coming week hoping he can get it in gold and green I've seen on the 'bay. I know it sounds petty, but damn that thing is gorgeous.
I intend to use my PC as my primary signal source through a Yaqin CD2 Tube Buffer that arrived Wednesday and I can't wait to hear on my current rig. I've archived over 2TB of music, CDs in FLAC and LPs to HDD at 24bit/192k. I plan to add a TT to this rig later. I fully expect the TT to sound better than the PC but my PC is at the bleeding edge and was built to archive and playback movies and music.
I have several friends into valves and a connection for the Shuguang Black(Treasures?). I've heard the Blacks in a couple of Carver tube amps, the Silver6, Silver7 and Bob's 20 tube monster the Silver9. They outperformed the KT88 Silver Eagles originally installed in the amplifiers...according to Bob.
Since this will be my first trip to the 'Dark Side' tube wise, what can I expect? I know what I'm hoping for, but how will it compare to nice SS gear?
Thank you for any replies and of course what you've all already written and contributed here, it's been a huge help to me.
ray
I found the Canadian Supplier that has warranty coverage and does some on-site adjustments in his shop, and I'll pull the trigger on this sale in the coming week hoping he can get it in gold and green I've seen on the 'bay. I know it sounds petty, but damn that thing is gorgeous.
I intend to use my PC as my primary signal source through a Yaqin CD2 Tube Buffer that arrived Wednesday and I can't wait to hear on my current rig. I've archived over 2TB of music, CDs in FLAC and LPs to HDD at 24bit/192k. I plan to add a TT to this rig later. I fully expect the TT to sound better than the PC but my PC is at the bleeding edge and was built to archive and playback movies and music.
I have several friends into valves and a connection for the Shuguang Black(Treasures?). I've heard the Blacks in a couple of Carver tube amps, the Silver6, Silver7 and Bob's 20 tube monster the Silver9. They outperformed the KT88 Silver Eagles originally installed in the amplifiers...according to Bob.
Since this will be my first trip to the 'Dark Side' tube wise, what can I expect? I know what I'm hoping for, but how will it compare to nice SS gear?
Thank you for any replies and of course what you've all already written and contributed here, it's been a huge help to me.
ray
Yaqin mc100
Hi everybody,
A full description of yaqin problems, how to solve them and how to improve the performance can be found on:
*** frihu.com *** Yaqin MC100B Verstärker-Tuning, Billiges Röhrenverstärker-Vergnügen(?) aus dem Land des Lächelns (1)
it is in german but can be translated, beside you will get all asistance you need at frihu...
Best regards to all,
Hi everybody,
A full description of yaqin problems, how to solve them and how to improve the performance can be found on:
*** frihu.com *** Yaqin MC100B Verstärker-Tuning, Billiges Röhrenverstärker-Vergnügen(?) aus dem Land des Lächelns (1)
it is in german but can be translated, beside you will get all asistance you need at frihu...
Best regards to all,