# Echophone Radio Corp. 20 Schematic

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 Model: 20 Manufacturer: Echophone Radio Corp. (Hallicrafters)

## Schematics Content:

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#### Page 1:

PAGE 3-6 ECHO.

MODEL 16,17,1e
Notes

Models 10, 15, 20-16, 17, 18
Short and Standard Wave Superheterodyne

CIRCUIT

The Echophone Models 10, 15 and 20 employ the same chassis, the only difference being
in the cabinets, the speakers and the connection of the power transformer. The Model 10 has
a single 8" speaker and Models 15 and 20 have dual 8" speakers.

The Echophone Model 10 is an 8 tube combination short and standard wave receiver em-
ploying triple grid, pentode and the'new duplex diode-triode detector tube. The >circuit con-
sists of an R. F. stage using a type 58 tube; a first detector (which operates as an I. F. tube on
the short wave bands) using a type 58 tube; an oscillator stage using a type 57 tube; a 175KC
I. F. stage using a type 58 tube; a combined second detector, automatic volume control and first
audio stage using a type 55 tube; a push pull output stage using two type 247 tubes; and a

l power supply using a type 280 tube.

_ The R. F. tube is not used on the three short wave bands, and the antenna is coupled to
the grid of the oscillator tube through a small adjustable condenser. Should the oscillator stop

>oscillating on the shortest wave band, thiscondenser capacity should be decreased slightly.
>The oscillator coil is tapped for the three short wave bands and has two tickler coils in series.

On the two shortest bands the larger of the two ticklers is short circuited.

The first detector and oscillator are inductively coupled and when operating on short
waves the grid of the first detector tube is switched toan I. F. transformer having its primary
connected in the plate circuit of the oscillator tube, there by providing an extra I. F. stage for
short wave reception.

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 amplification. 

The output stage consists of two type 247 tubes in a resistance coupled push-pull circuit.

The filter circuit consists of the 1200 ohm speaker field (on the Model 10) and two 8 MF
electrolytic condensers. A bucking coil is used in the speaker to keep the field ripple out of
the voice coil.

The Model 15 and 20 chasses employ dual speakers with fields of 4000 ohms each con-
nected in parallel. The power transformers in the Models 10, 15 and 20 are the same, the high
voltage plate supply winding being tapped. The tapped portion of the winding being used on
the Model 10 chassis and the full winding is used on the Models 15 and 20 to provide the extra
voltage necessary to excite the dual speaker fields.

NOTE: The voice coils of the dual speakers are connected in parallel and must bear
the proper relation to each other. To check this connection, disconnect the voice coil of the
speaker without the transformer mounted on it. An increase in volume With this coil discon-
nected indicates that the voice coils are reversed, and should be corrected by inter-changing
the red and green wires leading to the speaker without the transformer.

Models 16, 17, 18

These models are similar to the Models 10, 15 and 20, excepting that they are not de-
signed for short wave reception and that Shadowgraf tuning has been added.

The oscillator and R. F. Coils are different from the coils used in the Models 10, 15 and
20, and the oscillator tube is a 56 instead of a 57. The first detector was changed from a 58 to
a 57 tube. The Shadowgraf tuning device works on the same principle as the more familiar meter
tuning devices, excepting that a shadow of varying width instead of a meter band is used as
the indicator.

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