This 5V regulated power supply for the 300B filaments was posted by Suncalc and details about the regulated circuit are in the 300B SET Design Project forum thread. In an email exchange with Gio he recommended that I try the LT1085 voltage regulator circuit shown in Figure 2 for the 300B filaments. In my initial attempt I tried two 7805 voltage regulators in parallel for each channel but the current draw from the 300B heater filaments was too large for the 7805 IC. To improve on this idea I decided to use 5V integrated circuit (IC) voltage regulators for the 300B filament supply. In the original SE 300B schematic a solid state filtered DC power supply is used for the 300B filaments. The power transformer (T2) is shared between both audio channels of the SET amplifier.įigure 2 - 5V Regulated Power Supply Schematic for 300B Heater Filament For the small anodes chokes I specified 200H, 40mA (L1) and for the tube power supply chokes 6H, 225mA (L2). The power transformer and chokes are from a local manufacturer here in Greece and built to custom specification. Lundahl is a leading manufacturer of audio transformers and the Lundahl LL1623 transformers uses a special audio C-core. In my experience, a high quality audio output transformer is required for superior performance with SE tube amplifier circuits. By reducing the size of R8 you can increase the B+, but note that the maximum anode voltage for the 300B triode tube is 450V.įor the audio output transformers (T1) I used Lundahl LL1623 Transformers (90mA) - PDF (52kB). For more detailed information on tube rectified power supplies see these notes on vacuum tube power supply design. Using a separate tube rectifier (5U4-GB) for each channel results in a decreased voltage loss across the tube rectifier. While the power transformer (T2) is shared between both channels, each audio channel has separate rectifier, chokes and filter capacitors. To further improve performance from this 300B triode amplifier the power supply filtering sections have been duplicated for each channel. R7 was adjusted from the original value of 27k to 15k to attain the target voltages. For improved performance an anode choke (L2) was been added to each channel. To adjust the B+ I introduced a resistor in the power supply (R8). I did not deviate all that much from the original SE 300B schematic that I was following. Remember that the maximum anode voltage for the 300B triode tube is 450V.įigure 1: 300B Single-Ended-Triode (SET) Amplifier Schematic The voltage at these test points will change slightly with different tubes sets so don't expect to match the shown voltages exactly. 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. Keep this in mind as you are making up a parts order list for this 300B SET amplifier project. 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. 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 exact values and brands of the parts that I used for my SE 300B triode amplifier build are shown in Figure 1. A pair of reasonably sensitive (>91 dB/1W/1m) loudspeakers will be required with this 300B SET amplifier. The output stage is a SE 300B triode and the maximum power output is about 8 Watts per channel. This 300B Single-Ended-Triode (SET) amplifier circuit uses a direct coupled 6SN7 driver stage. For this SE 300B triode tube amplifier build I have used premium parts throughout, Lundahl audio output transformers and a DIY chassis. Specifically recommended in the circuit notes was that premium output transformers and components be used for the 300B amplifier build. Morrison's SE 300B tube amplifier circuit which I will refer to as the "original schematic". Please take a look at the SE 300B schematic for a description of Mr. 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. Photograph 1: DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier I have assisted by translating, formating and presenting his DIY 300B triode amplifier project. 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. This DIY 300B triode amplifier project was completed by Stamou Tasos who is from Greece. DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier
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