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Yaqin MC-5881A amplifier improvements
Yaqin MC-5881A amplifier improvements
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Old 19th September 2013, 11:16 AM   #161
sdcz is offline sdcz
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Quote:
Originally Posted by CityPooh View Post
Tubes in my 5881 are now: KT77 Genalex Gold Lion, pair of Telefunken PCC189 in the middle and Philips PCC85.
Same Philips tubes in tube DAC.
Hi Jaro,

If I upgrade my output tubes with the Genalex Gold Lion KT77 tubes, do I need any further amp modifications or would it be just a direct replacement?

Thanks,
Sonny
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Old 24th March 2014, 12:48 PM   #162
CityPooh is offline CityPooh  Slovenia
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Quote:
Originally Posted by sdcz View Post
Hi Jaro,

If I upgrade my output tubes with the Genalex Gold Lion KT77 tubes, do I need any further amp modifications or would it be just a direct replacement?

Thanks,
Sonny
Sonny. Good question for tweakers with the measurement instruments. I my Yaquin i have now KT77s for two years and they "works" as they did, no sweat, first day.
Last improvements. Silver coated banana inlets. Better depth, stiffer more deep bass, bass nuances are now much clearly listenable.

Gaofei rhodium coated RCA inlets(good ones, they looks similar to WBT Nextgens)and Eichmann Phonopod MK1 RCA inlets.
Both of those are having very different, nice "sound character", so it is easy to adjust the sound of the system and tubes with plugging interconnects in Gaofeis and then in Phonpods to find most listenable ones.
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Old 7th July 2014, 11:46 AM   #163
nissefar is offline nissefar
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Quote:
Originally Posted by Salas View Post
Lift one 500 Ohm from each pair. This will get the bias down from 70ma to 40 mA. Right now each tube dissipates 26W (overspec). You will measure around 40VDC on each 500Ohm left in circuit, and feel the heat backing off seriously enough. Do that and let me know how many cables go from PCB to chassis and from where off the circuit gnd points.
I've had the exact same heat problem with my 5881A.

I measured 6,7/6,8 heater voltage and similar voltages to the 500R's. Lifted one of the resistors made it run cooler but still a bit hot.

Do you think it is worth while to try to drop the heater voltage as well? If so what resistors do I add where?
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Old 14th August 2014, 08:19 AM   #164
CityPooh is offline CityPooh  Slovenia
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Quote:
Originally Posted by CityPooh View Post
Sonny. Good question for tweakers with the measurement instruments. I my Yaquin i have now KT77s for two years and they "works" as they did, no sweat, first day.
Last improvements. Silver coated banana inlets. Better depth, stiffer more deep bass, bass nuances are now much clearly listenable.

Gaofei rhodium coated RCA inlets(good ones, they looks similar to WBT Nextgens)and Eichmann Phonopod MK1 RCA inlets.
Both of those are having very different, nice "sound character", so it is easy to adjust the sound of the system and tubes with plugging interconnects in Gaofeis and then in Phonpods to find most listenable ones.
Update.
I mounted moderately used WBT-0210 cu nextgen RCA socket purchased for mere 20EUR.
On the other side of the interconnects, on tube DAC is Eichmann PhonoPod HC-XTC RCA female chassis socket.

Interconnects are my own brandname, Mantra, Strato audio standard, skin effect free, microscilations free, solid core wiring gold plated pure silver and silver-copper alloy. Plugs are Eichmann Silver Bullets.

A month before i made digital BNC Mantra Space audio standard cable prototype on Oyaide SLSB BNC Plugs for my tube DAC. I have other Oyaide products, mainly on mine Mantra Space power cables, so i know their products philosophy very well. Like Eichmann, on the softer side of the sound with a lots of clear, sweet sounding microdetails- if they are tuned exactly with the good audio cables and inlets. Without tunning, still good and listenable, but their potential will be not fully used.

WBT Nextgens(forget non Nextgen WBTs) are different story. Neutral, not soft, not hard sounding, exact("punktlich" in German language, that is their philosophy from the times of the Bismarck on)

Gaofei Rhodium RCAsockets kicked out in the first listening test, i wont waste words for comparision. Still usable, but only for subwoofers, like CMC silver sockets.
Best of the three in that test should be- Neutrik RCA socket. They offer certain satisfaction for blending the sound of average components, their sound-filtering characters are very different.

WBT-0210 Cu Ms Nextgens are, surprisingly, everything that WBT claims in their datasheet and more.
Compared to the excellent Eichmann Phonopods, there is a good listenable nuance of properly presented and positioned stage with WBT sockets more.
They are horrific component. Not just a socket, they "act" and sounds like superb audio component. They need a week to burn in.

Combo of those sockets is marriage made in heaven.
Next logical step was ordering a pair of Wbt - 0210 Ag Ms Nextgen Silver.
0210 Cu model is horrific, there is nothing bad to say abut it, i cant even imagine better RCA socket.

But.
WBT itself have Ag model to compare with Cu, which is "very easy to live with", so i wonder what Ag model has more to offer?
0210 Nextgen model are builded technically the same as Eichmann built his revolutionary Bullets.
To "act" like a wire.
But Eichmann Phonopod and also "classical WBT" sockets are not exactly builded like Bullets!
Only WBT Cu Nextgens s are, if we believe(and i do) to what WBT claims between the lines in their techincal specs!
And listening and comparing combo of that on the good tuned wires, make this simple technical fact obvious..
Combo Cu-Ag is very promising, but...

Listener cant say nothing in forward.
Listen to the music and forget plugs, sockets, wires and comparision and after weeks, or months, your brain will inform you, if you like it or not, about the differences of the technical items you installed.

Last edited by CityPooh; 14th August 2014 at 08:29 AM.
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Old 15th September 2014, 05:16 PM   #165
dubtown is offline dubtown  Germany
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Here are some improvements I received via Ballad Audio.
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File Type: jpg IMG_0632.jpg (781.4 KB, 252 views)
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Old 6th December 2014, 07:49 AM   #166
dubtown is offline dubtown  Germany
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The improvements from Ballad Audio was lousy. Frihu took the 5881 and rebuild it. His customize was really great, the amp now sounds really good!

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Old 12th March 2015, 06:31 PM   #167
Junb is offline Junb  Abu Dhabi
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Default Yaquin 5881

Quote:
Originally Posted by triode_al View Post
I finalised repairing the Yaqin.



I found that the transformer has 0,45 V per winding so I needed to take out two windings. In fact I just soldered a little wire after scraping off the isolation. It is now 6,3 volt AC.

Next I also did the following changes:
  • 1 - add a 20 ohm resistor to the high voltage AC;
    2 - add an RC stage in the high voltage supply: 4 muF plus 100 ohm 10 W. The capacitor is a Shizuki, a bit expensive but really worth the result. The rectifier has no overshoot. The Vb is now 405 V.
    3 - change the 5k1 feeding the drivers to 12k. This gives the driver stage a healthier 345 V.
    4 - I changed the output configuration: from ultralineair to triode connected. This is done by taking out the UL wire to pin 4 and connecting pins with a 47 ohm resistor. As well the cathode bias resistor must give -45 Vg @ 65 mA total (Tungsol specs). I opted for 600 ohm autobias, giving a measured Vg of -31 volts @ 25 mA each tube.
    5 - I changed the feedback. The original circuit gives 41 dB amplification, good for an iPOD but useless in a normal installation with a CD. I replaced the 5k1/100pF with 1k2/500pF(mica). The amplification is now 28 dB. The volume works fine now.
    6 - I also changed the feeding resistor for the drivers from 5k1 to 12k. This gives a Vb for the drivers of 345V. This is good.
    7 - not really trivial: I bypassed the electrolytics on the SRPP with 220 nF. The MKP coupling caps are fine just as they are.
    * I did not elevate the heater voltage. The drivers are at a DC level of 102L/105R volt, but the 6N1 or ECC85 can withstand that.

The result is very good, a clean sounding amplifier. No hum from the powersupply. No his.
Harmonics are very clearly heard in complex music (classical, strings).
Soundstage (depth) is easily perceived.

I play on an ESL57 from Quad. Not an easy speaker to use! But this amplifier shines. The CD I use is a Philips one with TDA1541A(*). A good reference.
albert
Sir i have this tube amp that is oveheating and i read your revision on it and i want it to apply in my 5881 amp if you dont mind sharing it in diagram(drawing) im new in troubleshooting amplifier and just want to calm it. Thanks junb
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Old 28th February 2018, 07:40 PM   #168
irondutchess is offline irondutchess  United Kingdom
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I realise this is an old thread, but I just purchased one of these.
They must have changed the design somewhat as there is no sign of hum or hiss even at high volume. This was tested with my DUNE HD Smart H1 connected and with nothing connected.
The valves heaters do look like they a running a bit hot, so maybe they are still a bit over voltage, I'll check at the weekend.
Overall I'm pleased with the way it performs for the price, but although it has less power, I still think I prefer the sound from my Lafayette LA-224B with its Russian gold grid quad set.
I'm not going to use it again until I have checked the heater voltage. When I do I will take some pics to compare the build to those already posted.
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Old 1st March 2018, 08:17 AM   #169
irondutchess is offline irondutchess  United Kingdom
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Question:

When testing transformer heater voltage output, do you test it with all the valves in or out? I ask because pulling one of the 6E2 magic eye tubes and testing pins 4 & 5 only shows 2.9V with all the other valves in place, despite this low reading all the valves glow somewhat brighter than they do in my Lafayette LA-224B and the amp seems to work okay.
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Old 1st March 2018, 09:23 AM   #170
irondutchess is offline irondutchess  United Kingdom
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As I'm not working today, I decided to investigate further. On removing the bottom cover it became clear that the 6E2 valve heaters were fed from the PCB not directly from the transformer as the other valves are. That low voltage may be by design for some reason. On removing the valve guard and pulling one of the 6N1 valves, I got 6.94V which is just about 10% over, should I try to bring this down to 6.3?

The first difference I noticed to the O/P picture is the change in the valve guard design. Looking inside, they have changed the orientation of the centre transformer by 90 degrees and added stiffeners. They have also done away with (though still mentioned in the manual) the Speaker/Headphone changeover switch. The Output valve bases now mount above the board not through it as before. There is also a 110/240V changeover switch, I'm not sure if this was in the original design?

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