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How to Build a Two-Stage Detector-Amplifier Unit
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SUPPORT BRACKETS (Material Brass H'Wide)
FIG. 6
The angle bracket details. Two are required
ally designed as the audio unit for the two stage radio-frequency amplifier described in the May, 1925, Radio Broadcast.
The circuit comprises a vacuum tube detector with variable grid leak and independent filament rheostat and a two-stage audio amplifier with filament controlled by one rheostat. Large core audio-frequency transformers of a ratio of approximately 3 to 1, and a C battery bias upon the grids of the amplifying tubes are important items entering into the construction. None of the adjustments is exceedingly critical but are found to be of actual necessity when maximum service is desired.
All thebindingposts for theconnection of the tuner, batteries and loud speaker are mounted upon the rear of a bakelite shelf which also supports the audio transformers.
A filament switch, the grid leak and condenser, rheostats, sockets and jacks are mounted upon the panel. The bakelite sub-base is mounted upon the brass angle brackets which are fastened to the back of the panel.
WHAT PARTS TO USE IN THIS UNIT
CATISFACTORY results with this design ^ depend entirely upon the selection of many of the same parts as employed in our construction. This is quite logical. It is probable that another type of amplifier can be designed using other parts — but that's another story.
The parts employed in the construction of this unit are listed as follows:
-panel mounting
3 Federal sockets2 Bradleystats
1 Bradleyleak, with .00025 mfd. condenser
2 Carter Jacks, 1 open single-circuit, 1 closed single-circuit
2 Rauland Lyric audio-frequency transformers ratio 3.95 to 1 1 Carter filament switch 1 Panel 7 x iox^ inches 1 Panel 3I x 9T3g x T3g inches 10 Eby binding posts Brass strip 20 x \ x \ inches Bus wire — lugs
14 \ inch x j6^ Round head machine screws
with hex nuts. 6 \ inch x y6¥ Flat head machine screws
with hex nuts 1 .0005 mfd. fixed condenser
The reader will probably ask, "can other transformers be used instead of those shown?" Of course, yes, but so can other parts be used throughout the construction. If this variation is allowed in parts selected, the individual constructor would have to lay out his own job. He would, of necessity, have to rearrange the
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SUB PANEL 3/i6"x3^x93/a"
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FIG. 5
In the layout of the sub-base, the dimensions are marked starting from the center line. By actually placing the audio transformers in place, their mounting holes may be scribed