![]() Line Transformers Redux + Art Dudley + AQ Dragonfl.A second part order was made last friday. This is where the cathode-follower version rapidly answered most of my questions. cathodyne) phase inverter and a fixed-bias output stage with a negative feedback loop to tighten up the response. Then I knew that the 4S couldnt drive my Yamaha M-50 solid state amp. Central elements of the design included a cathode-follower tone stack with independent bass and treble controls that were effectively driven by a 12AY7 preamp tube (a lower-gain relative of the 12AX7), a split-load (a.k.a. Happy Holidays and a Great New Year to All! I ordered the parts I didnt have in ordre to build the 4S, but in the meantime I learned about something called output and input impedance.This combination is as close as I could get to my 76/6SN7 line stage.īut don't limit yourself to this report, use it as a starting point for your loctal tube rolling adventure. Each half of the 7AF7 is direct coupled to half of a 7N7 configured as the cathode follower. The slightly lower transconductance and amplification factor mimics the exotic tonal qualities of its grandad, the 76. ![]() My ears finally chose the 7AF7 as the voltage amplifier for the line stage. I made an exception in wiring this line stage so that I could exploit the 7AF7 vs. And at typical line levels, the distortion should be almost nonexistent. This should drive any typical line, even one of extended length, without problems. Typically, I don't split halves of twin triodes for left and right channels. Overall distortion peaks at 0.4, output impedance is just 828 plus the 1k series resistance, and the total drive voltage loss is only 0.6dBv. ![]() However, it was too much for a zero feedback single stage line amp. With an amplification factor of 48, the 7F8 may not have enough gain as a phono preamp with the RIAA EQ in the negative feedback loop. But ultimately, it was the ubiquitous 7N7 (loctal 6SN7) that gave me the tonal balance I wanted, with the 7AF7 as alternate. Heres why: the only reason we would use a White cathode follower is to drive some low-impedance load, such as a 600-ohm transformer primary or headphones. Of course it is a follower and will follow the input voltage, but for a very short period it will draw grid current if the signal swings too fast and too high. As the tube has high amplification (100), its bias at this current is only -2V. I initially set up the phono section to use the unique 7F8 loctal in the cathode follower position, hoping that the 7F8's greater transconductance will produce a darker and more robust sound. dice45 said: The 12AX7 is meant to run at 1.2 mA with a plate supply of 250V.
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