Echophone Radio Corp. 14 Schematic

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Manufacturer:Echophone Radio Corp. (Hallicrafters)

Schematics Content:

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Models 5 and 14 Superheteroclvne


The Echophone Model 5 is a six tube Superheterodyne employing triple grid Pentode and
the inew duplex diode-triode tubes and having automatic volume control, The circuit consists
of one stage of R. F. amplification using a type 58 tube; a combined detector and4 oscillator
using a type 57 tube; one stage of 175 KC I. F. amplification using a type 58 tube; a. combined
second detector, automatic volume control and first audio stage using a type 55 tube; an out-
put stage using a type 247 tube and a power supply using a type 280 tube. `

The first detector-oscillator circuit employs a plate coil in series with the primary of the
first I. F. transformer, which is coupled to a coil in the cathode circuit of the oscillator tube.
A third` coil, coupled to both the plate and cathode coils is tuned by one section of the gang con-
denser and is made to track with the antenna and R. F. circuits by means of a fixed series con-

ln lining up the circuits at the high frequency end of the band care must be used in
adjusting the trimmer condenser on the R. F. Section. If this trimmer is tightened too much
the reaction between the R. F. and oscillator circuits will cause the oscillator to stop oscillating
or shift to the frequency of the R. F. tuned circuit. This shifting can readily be recognized by
tuning to a lower frequency where it will be found that the dial calibration is far from right and
all the tuned circuits are out of line with the oscillator.

The volume control acts on the audio circuit by varying the input to the audio portion
of the 55 tube.

A type 55 tube is used as a full wave rectifier for the second detector. The rectified R. F.
voltage developed across the input of this tube is fed back to the R. F. and I. F. tubes to provide
the automatic volume control action. The grid, cathode and output plate of this tube are used
as a triode to give audio ampliiication.

The filter circuit consits of two 8 MF electrolytic condensers and the 1500 ohm speaker
field. The speaker field is in the negative lead and a part of the voltage drop across it is
used to bias the grid of the power tube. A bucking coil is used in the speaker to keep the field
ripple out of the voice coil.

plate of the power tube and ground.

The model 14 is similar to the model 5 except that Shadowgraf tuning has been added.
This device operates on the same principle as the more familiar meter tuning devices, except-
ing that a shadow of varyingwidth instead of a meter band is used as the indicator.

The tone control consists of a variable resistor and fixed condenser in series across the -

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