DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier

This DIY 300B triode amplifier project was completed by Stamou Tasos who is from Greece. As a thank you for the 300B amplifier schematics, Stamou has shared with us his implementation of the 300B single-ended (SE) tube amplifier schematic by J.C. Morrison. I have assisted by translating, fromating and presenting his DIY 300B triode amplifier project. – Giovanni Militano – Editor

The circuit that I decided to follow for my 300B triode amplifier I found on this site, the 300B Single-Ended (SE) tube amplifier schematic with direct coupled 6SN7 input stage. Please take a look at the SE 300B schematic for a description of Mr. J.C. Morrison’s SE 300B tube amplifier circuit which I will refer to as the “original schematic”. Specifically recommended in the circuit notes was that premium output transformers and components be used for the 300B amplifier build. For this SE 300B triode tube amplifier build I have used premium parts throughout, Lundahl audio output transformers and a DIY chassis. This 300B Single-Ended-Triode (SET) amplifier circuit uses a direct coupled 6SN7 driver stage. The output stage is a SE 300B triode and the maximum power output is about 8 Watts per channel. A pair of reasonably sensitive (~91 dB+) loudspeakers will be required with this 300B SET amplifier.

DIY 300B

The exact values and brands of the parts that I used for my SE 300B triode amplifier build are shown in Figure 1. You should expect that the values of R7 and R8 will need to be adjusted slightly in order to achieve the target voltages shown in the schematic. The schematic shown in Figure 1 is for one channel only with the exception of the power transformer (T2) which is shared between both amplifier channels. Keep this in mind as you are making up a parts order list for this 300B SET amplifier project. The voltages noted in Figure 1 are measurements from my 300B triode amplifier build and compare closely to the voltages shown on the original SE 300B schematic. The voltage at these test points will change slightly with different tubes sets so don’t expect to match the shown voltages exactly. Remember that the maximum anode voltage for the 300B triode tube is 450V.


For more detail: DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier

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