The design is a two-stage, but with an octal tube – the more linear indirect-heating 6SN7. These tubes and the cathode follower configuration of second stage give very low distortion, low output impedance and an incredible low frequency response.
To get more gain, a 6SL7 tube could be used in input stage, but a higher power supply voltage, about 450V, is suggested. Both the 6SN7 and 6SL7 can work at 450V, requiring only changes to the bias resistors on cathode. With the 6SL7, the anodic resistance must be about 100K 1W instead 22K 2W.
About passive components types, I don’t leave many choices: Allen Bradley resistors on anode, Holco or Caddock resistances on cathode, ELNA Cerafine capacitors on cathode and power supply, and the DACT stepper attenuator. For all my new projects, I am using the very good ELNA Cerafine capacitors that I love and which can be find for a good price at Welborne Labs. The ELNA Cerafine capacitors contain super fine ceramic particles which, through chemical reaction, improve the discharging speed between the anode and electrolyte with very low distortion. Any other electrolytic or polypropylene capacitor is trash. Only the Blackgate WKZ could give better sound, but I have not tested it.
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