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7A19: Difference between revisions
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The 7A19 has no variable gain control. An option (#4) was available that added a variable signal delay (±0.5 ns implemented using a mechanically variable passive delay line), intended to match timing between multiple channels. | The 7A19 has no variable gain control. An option (#4) was available that added a variable signal delay (±0.5 ns implemented using a mechanically variable passive delay line), intended to match timing between multiple channels. | ||
The pre-charge setting on the input coupling switch is intended for situations where there might be residual charge on the input coupling capacitor that could overload the input. To use it, one sets the switch to PRE-CHG before connecting the input signal, then waits two seconds before switching to AC (LF point is | The pre-charge setting on the input coupling switch is intended for situations where there might be residual charge on the input coupling capacitor that could overload the input. To use it, one sets the switch to PRE-CHG before connecting the input signal, then waits two seconds before switching to AC (LF point is 1 kHz). The PRE-CHG setting also serves as a ×100 attenuator having a 5 kΩ input impedance in series with 2 μF, extending LF cutoff down to 20 Hz. In the AC GND position, the input is disconnected from the amplifier and terminated in a capacitively coupled 50 Ω load. | ||
==Links== | |||
{{PatentLinks|7A19}} | |||
==Internals== | ==Internals== | ||
The 50 Ω input impedance of the 7A19 is provided by a pair of 100 Ω resistors in parallel. | The 50 Ω input impedance of the 7A19 is provided by a pair of 100 Ω resistors in parallel. | ||
The resistors are protected by a pair of fuses in parallel. | The resistors are protected by a pair of fuses in parallel. | ||
The manual explains that the motivation for using two fuses in parallel is | The manual explains that the motivation for using two fuses in parallel is to minimize the effect of the series impedance of the fuses. | ||
to minimize the effect of the series impedance of the fuses. | |||
The fuse part number in the manual (Littelfuse 279-100) appears to be wrong since the MICRO 279 series fuse has 25.4 mm long pins. | The fuse part number in the manual (Littelfuse 279-100) appears to be wrong since the MICRO 279 series fuse has 25.4 mm long pins. | ||
The correct replacement fuse is Littelfuse 273-100 which comes in a box of 5 labeled "MICRO 1/10A 273", it has 4.32 mm long pins. | The correct replacement fuse is Littelfuse 273-100 which comes in a box of 5 labeled "MICRO 1/10A 273", it has 4.32 mm long pins. | ||