WhitakerAudio JC Whitaker 20 W Stereo Integrated Audio Amplifier, Manual

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10 Notes and Tube Data
The basic design of the stereo amplifier is adapted from a circuit contained in the RCA Receiving
Tube Manual , dated 1975. Circuit descriptions are based in part on the text contained in that
publication.
10.1 Tube Characteristics
The data given here have been abstracted from the RCA Receiving Tube Manual (1975) to reflect
usage in this product. The illustrations are adapted from the RCA manual as well.
10.1.1 6U8A Pentode/Triode Tube
The 6U8A is a medium-mu triode and sharp-cutoff pentode tube well suited to use in high-fidelity
audio equipment, particularly in phase splitter and high-voltage gain applications. The 9-contact
pinout is given in Figure 10.1. In phase-splitter circuits, the pentode unit should drive the triode
unit.
Selected tube parameters are listed in Table 10.1.
Table 10.1 Key Parameters of the 6U8A
General Characteristics
Heater (ac/dc) 6.3 V, 0.45 A
Heater-cathode voltage
Peak value ±200 V max.
Average value 100 V max.
Direct interelectrode capacitance (approx.), triode unit
Grid to plate 1.8 pF
Grid to cathode, heater, and pentode elements 2.8 pF
Plate to cathode, heater, and pentode elements 1.5 pF
Direct interelectrode capacitance (approx.), pentode unit
Grid #1 to plate 0.01 pF max.
Grid #1 to cathode, heater, grid #2, grid #3, internal shield 5 pF
Plate to cathode, heater, grid #2, grid #3, internal shield 2.6 pF
Direct interelectrode capacitance (approx.), other
Triode cathode to heater 3 pF
Pentode cathode, pentode grid #2, internal shield 3 pF
Pt
G1p
G2p
H
Pp
K , G ,
p 3p
Kt
Gt
H Legend:
H = heater
K = cathode, pentode (p) or triode (t)
G = grid (1, 2, 3), pentode (p) or triode (t)
P = plate, pentode (p) or triode (t)
1
2
3
4
5
6
7
8
9
Figure 10.1 Terminal pinout of the 6U8A.