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Old 12th February 2009, 05:23 PM   #111
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Quote:
Originally posted by bbbing
Hi Triode Al

I am impressed with your results on the modification to the power transformer. I have a few questions before I attempt the mod since the power transformer on my amp is overheating.
1) Is the mod easy to do?
2) Does the power transformer still run hot
3) Do you re-seal the tranformer after the mod, or leave the it open without the isolation?

Cheers Bing
Dear Bing,
It is easy, though you need a sharp knife and scissor. The paper of the isolation has to becut, it is very good isolation paper, several layers exist and it takes quite some time before you have gotten through to the windings.
The last winding in the outer layer (see my picture) is 7,3 volt, and each winding takes off 0,455 volt AC, fully operational. So the third winding is the one I tapped by
  • 1 first moving the windings apart (at least a half a mm apart, using a screwdriver)
  • 2 Lifting it a bit (screwdriver again,)
  • 3 scraping the isolation and soldering a new output wire
  • - note that you could cut it and be ready too
I 'closed' the outer paper again but you can leave it open of course. This is cosmetic only. there is no hazardous element anywhere around.

Afterwards the heating of the transformer is very much reduced. Still after hours the housing is warm. I think of a slitted opening on the housing: on the back there are these small slits for ventilation, but there is no way i can go. An extra slit could be made on that housing cust below the top alu plate to let the air out again: that might be enough to reduce it.
Anyway, reducing the heater voltage from 7.3 to 6.3 volt already reduces the heat: the power reduces from somewhere around 125 watt to maybe 60 watt (in the suggested class A triaode configuration).

But really, it is a no-brainer, no problem. It saves many tubes too.
albert
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Old 13th February 2009, 03:05 AM   #112
bbbing is offline bbbing  Australia
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Thanks Albert

I will definitely give it a try. Like you, I was also considering a new PT, however in Australia, this will be an expensive excercise and it will involve some major surgery on the amplifier.

I even considered removing the transformer casing to allow more efficient cooling but this involves removing the PCB to get to the screws. Also removed the eye tube and associated circuit to reduce the current draw and i don't believe it serves any sonic purpose.

I will keep the amplifier in Ultra linear (not sure if this has any affect on the PT heat) purely because I prefer the sound on single ended pentode amplifiers over triode.

Fingers crossed & thanks again
Cheers Binger
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Old 29th March 2009, 09:42 PM   #113
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Changed 5881 bottles for used Soviet 6L6, all made in first half of 1960s.
I know they are not eqvivalent for 5881, but they are working OK now for a month with no overheating or buzz..
I ordered a kilo of them, to pick the best ones..
Huge improvement in control ..

Originals have Shuguang logo without Shuguang sign on them..

Those ancient bottles are working well with two pairs of NOS Philips JAN6922 and JJ ECC88...
Those JJs surprised me.
In DAC they sounded horrible and lean.

I changed Wima4 link caps in my tube DAC for Jantzen Superiors(huge improvement), and i put in it NOS Vostok(Vostok-East in English) 6N1P-EV..Prod. year 1978..
Amazing sounding bottle..
I give them to some of my friends and they are more than happy..
Wimas 4 and 10s are good caps, very musical, but JSs have very extended lows and highs and amazingly balanced and detailed sound compared to them.
And they are also very musical!!!

Tomorrow im changing link caps in MC5881 for JS also..
Next i will put Vishay bypass caps on them..

I changed all MKPs in my setup to Mundorf Supremes, Silver oils and mostly Jantzen Superiors, and wiring in all signal paths to Tempoelectric of different gauges, combined where necessary, with Burklin wire wrap..
My RCAs are Eichmann Silver Bullets and MC5881 performs beautifully in such enviroment..
Next step will be Tempoelectric internal wiring in 5881..

Those DIY wires are amazingly balanced, spacious and you can pinpoint musicians on the stage..
Real Valhalla killers.

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Old 31st March 2009, 09:35 PM   #114
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Jantzen Superiors in 5881 rocks..

Totally different sound character..
Imaging even more superb..

In few days they will burn in..(i like them for that)
Tubes now glows slightly blueish because Superiors have 1200V..
Not only Shuguangs 5881, even Russian 6L6 glows...

What about 6L6GT?
My local tube guru says:"No problem, go for it."

And factory electrolytic caps in my 5881 are Nichicons, so there is no need to change them..
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Old 4th April 2009, 07:23 AM   #115
Flyier is offline Flyier  Sweden
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Hi all MC-5881 owners,

Has any of you measured the temperatures on the top of both the
transformer casing and on the heat shield for the tubes?

I have measured on the top of the trafo, 35-36 degr C, and on the heat
shield ~56 degr. C.

Is this simalar to what you have seen?

BR
//Flyier
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Old 4th April 2009, 09:45 PM   #116
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I havent measured temperature, but i ran amplifier at few ocassions all day long without any problems..

Probably temperature of the shield depends on tubes fitted in the amp..
I will measure it with the 5881 and then 6L6..

Some funny results combining different tubes..

Combination of a pair of original 6N1 Shuguangs and a pair of Philips JAN6922, results that Philips is almost not glowing at all, but Shuguangs glows almost like 20W room lamp..

Sovtek 6922 is also glowing and even buzzing in combo with Philips 6922..




Next step will be Wima or Vishay bypass caps on Jantzen caps...

Jantzens Superiors bettered focusing, imaging, bass depth, speed and airyness of highs..
Previous very good stereo is now breathtaking..
Finger moves on strings sounds now clear even at very low volume level..
But i had to drill wider holes on plate, because Jantzens have wider wires..
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Old 5th April 2009, 11:04 AM   #117
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Quote:
Originally posted by CityPooh
--
Combination of a pair of original 6N1 Shuguangs and a pair of Philips JAN6922, results that Philips is almost not glowing at all, but Shuguangs glows almost like 20W room lamp....
CityPooh, if you measure the AC for the heaters than you might find it pushes in 7,2-7,3 volt
Some tubes will glow bright, they are made for 6,3 with low tolerances, and will damage the heater-cathode isolation fast.

If you do not change the heater voltage, then you should use a PCC88 or PCC189 for instance - these can take 7 or 7,3 with ease. And is pin-combatible.

alberti
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Old 5th April 2009, 03:39 PM   #118
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Thx for caring, Albert..

I will surely purchased tubes you recommended, probably from an ukraininan EBay seller that i trust 100%..

Im using in 5881 amazingly sounded pair of Philips JAN 6992 and a pair of JJ ECC88 combo, which glows as evenly as the four original 6N1 Shuguangs...

But when i mixed some pairs of tubes i have, in order to achieve best sonic results(they are all ECC88, 6922 and 6N1 and russian 6N1P, which is identical to chinese 6N1)there were some really unespected, odd results, in glowing of preamp tubes for some seconds and i always instantly shut off the amp and changed them..

Here we have now 21 celsius sunny weather coming from Mediteraninan, almost no winds and still 5 meters of snow at nearby Alps...

Here is the link to the amplifier of our local tube guru..

http://www.hajdinjaklabs.com/web/?p=25
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Old 4th May 2009, 04:07 PM   #119
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I have a weird experience with this amp :

there was a gap between very low bass and medium....some '70s recordings seemed to lack totally bass...same with most classical CD....

It was fitted with NOS Sylvania 5881 and Russian OTK1 6N1...

After trying EVERY tubes I have ( and I have a big collection ) , I tried 2 Amperex Bugleboy 12AU7 in the front WITHOUT modifying the heaters supply. Saying to myself, after all it's written 12AU7 (6N1) on the component board ).

And the amp came to life. Perfect tone.

How is this possible ???
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Old 4th May 2009, 04:08 PM   #120
zbodeoc is offline zbodeoc  Romania
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Default Yaqin MC-5881A improvements

This is my tribute to a beautifully made amplifier.

Iíve bought this machine from eBay for 30 Euros about three years ago and the transport from China put me back another 150 Euros. I was very happy when I received it in one piece. Playing this amp at half of the volume doesnít sound so bad but itís still far from what you can get. This amp has a very poor power supply, unfortunately. In fact, that single capacitor pollutes so badly the entire system with 4V ripple, which is far from sinusoidal having filthy harmonics.

Another major flaw is the position of the main transformer, aligned with the output transformers. This induces the noise that you canít get rid of it, no matter how many capacitors and chokes you add.

So, what I did? Hereís the list of improvements:

1. I had the main transformer rewound conservatively for 230V, period. You deserve better than messing around with the resistors which will emit heat and will not correct the nasty ripple (thanks Radu!)
2. I have lifted the main transformer 90 degrees. In fact I tried 3 toroids before and with all of them I had noise and excessive heat. The new main transformer, double shielded, is sitting now on plastic, does not make contact with the metal. You have this way enough room to add chokes and capacitors.
3. I have added 3 chokes and 2 capacitors in the power supply. The initial capacitor remained in the ďfirst line of fireĒ because it has a 125 degrees Celsius written on it (donít know if itís truth or not). Then Iíve added 1.7H choke, 330uF capacitor, another 2 chokes of 0.4H and the final capacitor which is a 20uF motor-run polypropylene having 25V/us. Now I have about 5mV SINUSOIDAL ripple on 5881 tubes, good enough for single-ended designs. Iíve added also polypropylenes in driver section.
4. I have modified the reaction with 3k3 resistor and 325pF mica capacitor, using coaxial cable to transport the signal.
5. I have replaced the signal capacitors with Russian paper in oil 0.22uF/ 500V. After this change first word coming to my mind was ďsilkĒ.
6. I have added a 6A/380V relay to high voltage branch for delay purposes.
7. I have replaced the rectifier bridge with BYT54M avalanche diodes (thanks Dietmar!)
These diodes are 300 times faster than 1N4007.

I wonít say itís easy, but the result is high-end, not bad at all for 180 Euros Iíve paid.

Have fun, take care, enjoy life and donít forget any (mili)second that youíre playing with lethal voltages!

Regards,
Dorin
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