Sometimes these different ratings can be misleading, as in the (unsubstantiated) story that the 1614 was picked for the Fisher 50 amplifier over the 6L6 because of its "higher" plate dissipation ratings. The design-maximum or absolute maximum ratings look enticing, because they are higher, but they require that the designer really do more homework on the circuit and power-supply tolerances so that these ratings won't be violated.


1 - 6026 Data Sheet, RCA Tube Department, Harrison, New Jersey, 1951.

2 - RCA Transmitting Tubes, TT-5, RCA Tube Department, Harrison, New Jersey, 1961, p. 84. (available as a reprint from Antique Electronic Supply).

3 - Essential Characteristics, 14th ed., Tube Products Dept., General Electric Co., Owensboro, Kentucky, 1973, p. 5. (available as a reprint from Antique Electronic Supply).

Subject: Tube Headphone Amp
I really enjoy your Webzine, and appreciate your efforts for us tubesters. Check out this headphone amp construction article on the Headwise website
Your comments would be appreciated. 

     A redrawing of the circuit from the Headwize site is shown above. My first take is that the first stage is being run far too lean,  the power supply is inadequately filtered, and that that the White cathode follower stage's plate resistor is far too high. In spite of these reservations, I am sure the circuit probably sounds pretty good as is. The modifications I would under take would be to replace the first stage's plate resistor with a FET current source, the CRO-470, as it would provide much better power supply noise reduction and then to replace the 3.3k resistor with 5k potentiometer (actually, I would use a 500 ohm potentiometer) so that the output stage could be tuned on a scope for the headphones you intend to use. I would certainly add a large valued film bypass capacitor across the output capacitor. (I would also experiment with using a photo-flash capacitor or two HF capacitors in series.) I would also play with reducing the gain by wrapping  feedback across the amplifier or by replacing the first tube with one that had a lower mu.

Coming Next Issue

   Next time around, we will update shunt regulators with a new design. We will also look reviving an old, but good topology for output stages. And we will take a look at designing a portable headphone amplifier.



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