300B Tube Amplifier Build

The 300B tube can be the holy grail of every tube amplifier. Everyone praises for its sweet sound. Personally, I never compare directly between one amplifier to another amplifier using 300B tube, but I still believe the reputation of this 300B is not a false statement.

More specific, the single ended 300B design are well known for the best sounding amplifier compare with the push-pull. Single ended is also more economical approach since we only need a pair of 300B tubes. But it has the drawback, it is the low power output. It is about 6 watt per channel.

That is why in this 300B tube amplifier build, I will make this amplifier in single ended design with 6SN7 driver and 5AR4 rectifier to drive a headphone.

For headphone? Pretty disappointed?

I guess not. I hope the sweet sound of 300B can be heard more closely to my ears.

I wish I can build this amplifier in point-to-point wiring. But right now, I already have this 300B amplifier PCB. This becomes simpler for my brain to not thinking so much in this building process.

The PCB quality itself is quite good and the components arrangement are okay. The schematic for this PCB can be found easily.

I start to populating all the components based on the marking on the PCB. The best things when using the PCB like this, it doesn't take so much time to fill this PCB with all components required.

The only modification I have here is cut the 5-volt heater trace, then connect them by using 0.47-ohm 5-watt resistor for each 300B tube. The reason for this is to improve the ripple rejection and lowering the voltage from 5-volt AC that come in to the rectifier and capacitor, then goes to the resistor to become 5-volt DC supply.

The transformers using in this amplifier are all custom build by the local.

The power transformer secondary is: 320-0-320 200 mA, 0-5 3A, 0-5 3A, 0-5 3A, and 0-6 2A.

The output transformer secondary is 600-ohm impedance.

The choke transformer is 5H 200mA.

I guess using famous hi-end audio transformer is not on my list and budget.

The box for this amplifier is also custom made by local. I design the dimension and ask someone to build it for me. Very nice build in my opinion.

The idea with all local made is I try to make this amplifier more affordable but without sacrifice the good looking and good sounding from the 300B tubes.

Now I preparing the layout for every component's placement on the steel plate. This is the most important things when building every amplifier, especially for the tube amplifier where the induction from the transformer is strong enough to make noise.

I will talk about this issue latter on my next post.

But for now, let's we enjoying the building process of this amplifier.

It is almost finished.

I need to double check the connection and the voltage before put the tubes, especially for the expensive 300B tubes.

Once they are all correct and the voltage from each tubes are all within the specification, now it is time to put the tubes on it.

I start from the 300B tubes. I am using PSvane 300B Cossor series.

The others tube such as a 5AR4 rectifier and a pair of 6SN7 driver tubes are all Russian made. They are very affordable tubes with great sound and durability.

This 300B tube amplifier for headphone is now finished.

I connect the source, plug the headphone's jack inside and plug the power socket to the power line.

Here it goes!

The amplifier has a loud hum on both channels. Very sad.

Although it is working perfect and to be honest, when I play the music, it sounds beautiful, but the hum level is cannot be tolerated.

This issue needs to solve and I still working on it right now.

Until then, see you.

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