MC-5881A
Yaqin MC-5881A
Yaqin MC-5881A
As an update to the information that follows I have heard from more recent purchasers of the MC-5881A that they have not had issues with hum and that voltages were within tolerance. The transformers are now mounted correctly to avoid magnetic field coupling - this suggests sensible reworking by Yaqin both in terms of design (ground issues and transformer placement) and safety…
This 5881A(6L6GC)/12AX7(ECC83) based 23wpc amp had some serious problems when I got it. The hum was terrible and mostly caused by a (number of) ground loops. There’s a thread on diyaudio.com http://www.diyaudio.com/forums/showthread.php?threadid=97618 that I participated in to resolve most of the issues. The final mods were as follows:
Yaqin MC-5881A with modifications
1. top and bottom left – some ground layout work (this may be trial and error – but the key thing is making all grounds go to chassis at the same point
2. middle left – one of the pairs of 500 Ohm 5 watt bias resistors removed
3. up and to the right is the resistor in the CRC filter. I used a 270 Ohm 20 watt which meant that I could leave the original 450v rated cap in place as it dropped sufficient volts to bring it into spec.
4. right of that is the 100uF 500V cap that makes up the CRC filter.
5. right of that is the other 500 Ohm bias resistor with its friend removed
6. right of that is the pair of 0.33 Ohm 10 watt resistors that drop the heater voltage to 6.3v
7. The other circle at the bottom right shows where I replaced the original 0.22uF coupling caps with (cheap) polyprops. The fitted originals were only rated at 275v, although the schematic suggests 400v. They only see that kind of voltage with the valves out of circuit, but they may be worth changing anyway. Note that all the yellow cylindrical caps are replacements – I just haven’t circled them all!
Click to view the schematic:
Yaqin MC-5881A schematic
Comments
Comment from Marcus Reinhard
Time: March 8, 2009, 10:18 pm
This side is very usefull.I own a Ballad Melody SP6MK3 which is exactly the same device. These amplifiers were designed in Hong Kong for a power supply of 220 V. When your voltage is more all voltages get higher. From filament voltage up to 7 V and a plate voltage of more then 350 V DC. That can get critical. That amps get so hot has mostly to do with a too high idle current. For a 6L6 or 6L6GC or 5882 or the 6P3Se it should be somewhere between 40 and 50mA. (calculate 50- 60 % of the highest plate current) You can put it on the “cold end” or more in the “hot end”. But there is a high power dissipation when you put it on the higher end (Class A) . As this amp uses “auto bias” You have to change the resistors in the cathode circuit from 2 500Ohms in parallel to 2 810Ohms in parallel. The sound is still very good !! Another strange thing is printed on the PCB.
Formerly they used a 12AT7 (ECC81) in the SSRP stage and a 12AU7 (ECC82) in the driver stage. Now they use 4 6N1P (-EV). Some newer versions also use 4 ECC85 !! As this are all different tubes I tried the following.
Put 6N2P in the SSRP stage (mathched ones, each triode system the same S and µ) and use 6N1P as a driver.
I would say it sounds great. Another advantage is that a 6N2P does not draw so much current. Putting 6CA7 should be possible (plate voltage and 6K Output Transformer) but these tubes draw more filament current.
So I’ve not tried it by now. If you compare the schematic of the MC-10L and the MC-5881A you will see what I mean. Put the auto bias away and the (not very good working) 6E2P magic eye circuit and the schematics are identic. Have a look at the resistor values !! Capacitors is o.k. I think they have used stronger power transformers and (perhaps ) better output transformes. If anyone has got “tuning” ideas so yust write me.
For exact meassing I’ve build my own adapters. Now I can meassure under real conditions.
Kind Regards M.Reinhardt
Comment from Steven Beesley
Time: April 5, 2009, 1:53 am
Hi I just purchased one of these off ebay after winning a bid paying GBP120.00 – Yaqin MC-5881A. Don’t know if there will be any issues, since I am located in Hong Kong on a voltage of 220V AC. You have a great site, very useful. The Yaqin MC-5881A is a good looking amplifier and for the cost, I really cannot argue!
Regards,
Steve
Comment from dragonX
Time: June 30, 2009, 9:52 am
Thanks for your help! I had to change the cathode resistors also, but would recomment to use a 11W 470 Ohm instead of only one of the 5W 500 Ohm provided.
If you own a Ballad SP6(+) also the first you should do is to change the cathode resistors (2* 500 Ohm/5W) to one 470 Ohm 11W. Out of the box it’ working at ~180W and producing enormous heat- and will be killing the 5881 tubes shortly)
Do the same to a new 5661 and you will avoid burning your house and buying new tubes in short time.
My improvements: Russian 6P3s (without ‘e’) matched quarts in the output stage, ECC85 and 6N1P-EV in the preamp and driver stage. And Wima MKP10 caps. – You my also put a 0.68mF/630VMKP parallel to the 470mF cap of the power supply. Don’t try other tubes besides the 6L6-family. You may achieve some sound improvements but they will not run properly. (May be for some time…)
Comment from dragonX
Time: June 30, 2009, 10:08 am
Oh, sorry! I meant ‘ do the same to a new 5881′- not 5661!!!!!
And i changed also the 100p caps of the feedback in ‘Glimmer-caps’. But I’m not sure whether this has any effect on the sound. 
Now I’ m very happy with the sound and enjoying the music which the yaquin provides. Every new amp which comes to my house has to compete. Wooden instruments (and brass also: shimmering) and voices come to live.
And….. as I wrote in the mc10l section: try both of the speaker connectors. Also if your speakers impedance is reading 8 Ohm, try the 4 Ohm connectors!! According to the non-linearity of the impedance of most speakers the amp will put out more power, the more impedance it ’sees’….
Connected spendors s8 (8 Ohm) and Rogers SP6 with the 4 Ohm plugs and got remarkble improvement.
Comment from Jku
Time: January 21, 2010, 8:02 am
Hi.
Last week I bought one MC 5881A from Shangahi. Now I am testing it and all this info is useful to read.
Yesterday I did open the amplifier and I noticed that the power transformer (220V ac) in on different positon as here on the photo! As here on the photo the transformers coils are in “line” and in mine the middle one is “turned” 90 degrees.
Obviously mine is as it should be: to avoid the magnetig field to penetrate in to the audio transformers coils to make hum.
Regards
Jku
Comment from Dan Ashby
Time: January 21, 2010, 1:51 pm
Thanks, Jku. I’ve added an update to this page to incorporate your information.
Cheers,
Dan
Comment from Harrie
Time: June 28, 2008, 9:22 am
Do you happen to know if the transformers in this amp are suitable for both 110 and 220V? I bought one on eBay, but the seller sent me a 110V, while I asked for 220.