The 300B Amplifier Updates

Welcoming this year, I always hope that this 2026 will be blessed with joy and happiness, with all things we are doing, we doing with fun and excitement.

For the past week, I actually got flu and not really into this hobby for quite long time. But I was concerning to revisiting this newly built amplifier again. Is not 100% complete, few things need to change and add to suit my sound preference.

So, here it is. The new updates for this 300B amplifier.

The above photo is the latest update for my 300B amplifier built based on Luxman MQ-300 amplifier schematic.

The line input goes to a 100K ohm potentiometer as a passive pre-amplifier, then goes to 6SN7 as line driver tie in parallel for each channel with gain of 10 times. From there goes to coupling capacitor before to the 300B grid.

Since the only pre-amplifier is just an input, a cable and a potentiometer, I think replacing the input cable to the better one, might improve the sound.

I am now using Mogami Neglex 2803.

Oh man! this Mogami 2803 is very hard cable to deal with. It is very stiff, the copper are silky thin and the isolator in the center is pain to solder together with the copper itself.

The cable price per meter is around $20, which is the most expensive for a small signal cable I ever bought.

The next components that I replace is the coupling capacitor.

Previously I was using Russian paper-in-oil capacitor K75-10. Very big capacitor compare with the one I using it right now is just a normal MKP capacitor.

With the K75-10 capacitor, the music is too slow for my preference. Sound signature more to the dark sounding with great musicality but less aggressive and details.

The last components need to add is the cathode bypass capacitor.

For every resistor on each cathode of 6SN7 need to bypass with 220uf capacitor. I forget to add it before and that is why the bass, the depth and the sound-stage seem shrink. This small and cheap component plays vital roles for tube amplifier to sound good.

And there all we have now.

The sound is improving so much, I think the most contributor components coming from the cathode bypass capacitors and then the coupling capacitor and lastly is the input signal cable.

I am now more enjoying this 300B amplifier especially during end of the year 2025 holiday, with a good music and great equipment.

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