• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Yaqin MC-100B - not as powerful as advertised, but still a good value.

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This is how I linked the soft-start device, between the main switch and the primary windings of the transformers network.
The voltage transformers grows slowly, from 30V almost to nominal value, in tens of seconds, thermistors are then short-circuit the relay contacts. Time after which the short-circuiting occurs can be adjusted with the trimmer potentiometer. The amplifier is very slow start.
 

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Reference Yaquin MC100 B PCB

Dear Friend,
Please inform me what were your Thoughts on The Yaquin 100B ( PCB Boards) How Thick are The Boards and Any Idea of THE TRACINGS are they 1 OZ or Are They 2 Oz Tracings , please let me know As I intend to purchase the YAQUIN 100B just to drive my JBL 2402 Super Bullet Tweeters and Use The CARY Sixpac For my JBL PARAGON Midrange Horns Coupled with The JBL 2380 Horn Flares. and my bottom end Speakers is The Klipsch K33 Bass Woofers, Driven with The AMCRON POWER LINE THREE SOLID STATE POWER AMP IN CLASS A MODE. I intend in using Class A With all My Power Amps.
My 8 Tube 3 Way Active Variable Crossover is The Famous LUXMAN A 2003 8 Tube Active Crossover, Which is Using Better Quality Metal Film 1 Watt Resisters and Better Quality Jansen Gold Oil Filled Capacitors.
I am countion on your knowledge of THE PCB Boards of The Yaquin 100B , in advance before Purchasing it.
Please respond Francis Jansz
fsj@iprimus.com.au
or Text: +61 403 146207
Melbourne/Victoria/AUSTRALIA
 
I am sorry, but I have no opinion on quality of boards in this amplifier. I didn't have problem with re-soldering components. So I think they are reasonably good. I sold this amplifier long ago, so I cannot comment on durability.
 
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Hi Charles I don't no if there is any advantage in going bigger. Google humble homemade hifi capacitor test. Jupiter copper foil paper & wax look good in this test. I had a slight hum on my right channel and changes all my power caps to bigger ones as I read bigger is normally better on power supplies. I changed the caps between the transformers to Rubycon MXK 400v 1200uf but had to carfully remove the plastic top covers from my old caps and fit them to my new caps. I also changed the six capacitors in the centre of the main pcb for larger 105c caps done the same to the two caps on the caps on the psu pcb. Sorry I cant remember the size and make. My amp is now dead quite if I turn the volume all the way up with nothing playing but as I say some of my caps had slightly bulged.

Removing the feedback loop made the biggest difference to the sound on my amp. It gives a bigger sound that fills the room more and seems more open and warmer with more bass I would say it sounds more like what I thought a tube amp would sound like. The down side is bass is not as tight and treble isn't as sharp up top and some say the added warmth and sound stage is distortion. To me it sounds best with feedback removed voices sound more real. You can do what I did and put a rocker switch in each side to switch the feedback loop in or out that way you can compare differences switch it to how you prefer.
 
Dave murrey said:
The down side is bass is not as tight and treble isn't as sharp up top and some say the added warmth and sound stage is distortion.
You are describing the classic effects of removing feedback from an amp designed to have feedback:
- higher output impedance, so poor control of the speaker bass resonance
- treble rolloff
- higher distortion

I had a slight hum on my right channel and changes all my power caps to bigger ones as I read bigger is normally better on power supplies.
There are diminishing returns as you go bigger in cap value. Bigger is not always better.
 
Thanks for that information DF96 I was wondering weather I was enjoying the sound of distortion but have tried both ways and it sounds better without feedback to me. I was thinking of trying to add resistors to the feedback in a attempt to have a in-between both sounds.

If I was clever enough I would just use the case/parts and build a hardwired amp from the best circuit because I read this is the best way. I have got Krell KSA 50 clone pcb kit I have started building and was thinking of trying this with a tube pre amp kit.
 
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Removing the feedback loop made the biggest difference to the sound on my amp. It gives a bigger sound that fills the room more and seems more open and warmer with more bass I would say it sounds more like what I thought a tube amp would sound like. The down side is bass is not as tight and treble isn't as sharp up top and some say the added warmth and sound stage is distortion. To me it sounds best with feedback removed voices sound more real. You can do what I did and put a rocker switch in each side to switch the feedback loop in or out that way you can compare differences switch it to how you prefer.

When you ad a 100k pot between the feedback pad, you can adjust to a point you like the sound most.

Replacing power and buffer capacitors for higher value caps can lower powersupply hum.

You must be careful with changing values of (de)coupling caps because they can be part of frequency filtering to protect the outputtransformer. Using other brands and types is no problem.
 
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