Baby HiFi
Figure 25 TYPICAL INTERMODULATION TEST OF AUDIO AMPLIFIER.
Audio tones of two frequencies are applied to input of amplifier under test, and amplitude of "sum" or "difference" frequency is measured, providing relative inter-modulation figure.
Figure 25 TYPICAL INTERMODULATION TEST OF AUDIO AMPLIFIER.
Audio tones of two frequencies are applied to input of amplifier under test, and amplitude of "sum" or "difference" frequency is measured, providing relative inter-modulation figure.
beneath the socket bolt heads, and lock nuts are used beneath the socket retaining nuts to insure a good ground connection. All ground leads of the first 12AU7 tube are returned to the socket, whereas all grounds for the rest of the circuit are returned to a ground lug of filter capacitor G.
Since the input level to the amplifier is of the order of one-half volt, the problem of chassis ground currents and hum is not so prevalent, as is the case with a high gain input stage.
Phonograph-type coaxial receptacles are mounted on the rear apron of the chassis, serving as the input and output connections. The four panel controls (bass boost, treble boost, volume, and a-c on) are spaced equidistant across the front of the chassis.
Amplifier The filament wiring should be Wiring done first. The center-tap of the filament winding is grounded to a lug of the 6X5-GT socket ring, and the 6-3 volt leads from the transformer are attached to pins 2 and 7 of the same socket. A twisted pair of wires run from the rectifier socket to the right-hand 6AQ5 socket (figure 23). The filament leads then proceed to the next 6AQ5 socket and then to the two 12AU7 sockets in turn.
The 12AU7 preamplifier stage is wired next. A two terminal phenolic tie-point strip is mounted to the rear of the chassis, holding the 12K decoupling resistor and the positive lead of the 10 /xfd., 450-volt filter capacitor. All B-plus leads are run to this point. Most of the components of the bass and treble boost system may be mounted between the tube socket terminals and the terminals of the two potentiometers. The feedback resistor Ri is mounted between the terminal of the coaxial output connector and a phenolic tie-point strip placed beneath an adjacent socket bolt.
When the wiring has been completed and checked, the amplifier should be turned on, and the various voltages compared with the values given on the schematic. It is important that the polarity of the feedback loop is correct. The easiest way to reverse the feedback polarity
Figure 26 20-WATT "WILLIAMSON-TYPE AMPLIFIER PROVIDES ULTIMATE IN LISTENING PLEASURE FOR THE "GOLDEN EAR."
Amplifier chassis (left) employs two low level stages driving push-pull 807 tubes in so-called "Ultra-linear" circuit. Power supply is at right.
Figure 26 20-WATT "WILLIAMSON-TYPE AMPLIFIER PROVIDES ULTIMATE IN LISTENING PLEASURE FOR THE "GOLDEN EAR."
Amplifier chassis (left) employs two low level stages driving push-pull 807 tubes in so-called "Ultra-linear" circuit. Power supply is at right.
3- voltage measurements made 7- punched and drilled chassis, with 1000 ohms/volt voltmeter STANCOff WMB
4- jacks Jl and ü2 are insulated
3- voltage measurements made 7- punched and drilled chassis, with 1000 ohms/volt voltmeter STANCOff WMB
4- jacks Jl and ü2 are insulated from chassis Figure 27
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