• 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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#41
Here I've replaced the screenresistors to kiwame (to blu/ye wire) but it's after this i get confused....😀
 

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#42
the OPT plate windings will have the higher dc resistance than the screen grid taps as measured from the B+ lead, so use the two windings with highest dc readings, take note of the color, if you interchange them, you are going to have motorboating.....

tape up or heatshirk tube the unused opt taps...
 
#47
Max Martin said:
Have anyone here tried to bypass/remove the UL/Triode buttons?

I want to connect my KT88 direct without any switches because i never listens to UL anyway. Triode sounds better in my ears!

I'm little unsure though how to do it. In triode-mode signal passes through the longest winding right and UL on two middle"taps"?

I ask before i do anything stupid 😉
Click to expand...

Why would you do this? This switch is reliable enough if you do not flip it several times a day. Leave circuit as-is. When you decide to sell, any mod will reduce the market value.
 
#48
I think the biggest upgrade to this amp would be to change the OPT's to some better ones - as this is usually the part making biggest difference. It is the most expensive part, and where the chinese "saves" money using quite bad stuff usually.
 
#50
AJT said:
if you can live with just triode mode, then removing the UL triode selector is imho a good move...

simply connect the screen resistor from pin 4 to pin 3 directly and you are done...then disconnect all excess wirings...
Click to expand...

It was the orange/white cable R = 172 0hm! Now it's working perfect and believe it or not but detail/transperancy/dynamic/smoothness are a step up in SQ. Little more electrostatic-sounding in my ears.. I used kiwame 180R /5W. Worth it for sure!
 

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#51
Since i only use my Yaqin MC100 over 150hz is it possible to reduce the cathode bypass cap to say 10-33uF to make a roll off higher up? I was thinking it makes the powertubes life little easier when they don't have to handle low frequencies and also maybe a boost in SQ?

I found this pic on the web (ECC83/12AX7) with 100K load impedance in this drawing and different values of cap? Legit?
 

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