Everything you need to build this is spoon fed. Instead of a compromise I fixed two output points into the design. The two output tubes that work in this application are similar, but have different operating points as a result.
It's optimized for a given output impedance with a given tube. The White Cathode Follower is a little different than most output stages. 4 jumpers are provided to switch between the (2) 6BX7 and 6BL7 output tubes. Uses (2) 6SN7 input tubes and (2) output tubes being either 6BX7 or 6BL7. Note that my case design is well ventilated. Another one that's a perfect fit is "1907E". Google "B18-HB Case" if you can't find one on Ebay. The CAD I used for my case is also shown above. Super thick PCB (2mm) with 2 ounce traces!!! Schematic shown above. All this circuitry is smartly arranged on a 6.50” x 7.75” board. I'm using a 470uF electrolytic with a 30uF film capacitor in parallel. Chassis ground tied through one of the mounting holes Designed for use with high end audio grade components (Wima MPK series, Nichicon KX and KW series, etc).
6SN7 CATHODE FOLLOWER FREE
House ground attach to the board for a hum free experience. Provides for hum free power and max heater/cathode difference isn't exceeded. Elevates the heater ground to ¼ of the B+ voltage. Additional Features: ¼ B+ reference circuit built in. Designed for external choke filter (C-L-C). Want to use a cool looking 5U4G instead, just ask how. I like the look of the extra tube and I like the slow start. High Voltage Circuit: Regulated output using Maida circuit. The transformer I use puts out 8A 6.3VAC. A safer rule of thumb is 2.0X the DC current. Remember you need 1.8X the DC current from your transformer. Heat sink on LDO and heat sinks on all rectifying diodes. High current components and heat management designed in. Trimpot adjustment to dial in the final voltage. Heater Circuit: Regulated 6.3VDC from 6.3VAC winding with the use of schottky diodes and super low dropout regulator. This will drive any pair of headphones you may own. After a few tries I made some great boards that work perfectly. With 6SN7 input tubes the entire heater draw adds up to 4.2A of DC current. To drive low impedance headphones with the Aikido circuit requires the use of 6BX7 or 6BL7 output tubes. The tricky thing was the power supply design with DC heaters in mind. I wanted to use a single standard power transformer with high voltage and filament supply. Sounds easy enough to pull off but the power supply requirements were a bit tricky. I chose an Aikido input with a White Cathode Follower output (input/output stage design credit to John Broskie of TubeCad). The original goal of this project was to have a compact octal tube OTL headphone amplifier that would drive low impedance headphones (down to 32 Ohm). The reception was great so I had more made and made a few improvements. I started this auction by selling extra boards from a personal project. Item: 132701966300 DIY PCB Board OTL Tube Headphone Amp Aikido White Cathode Follower 6SN7 6BX7.
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