Electro-Voice DB23 User manual

Slecho Voice
ELECTRO-VOICE, INC.
BUCHANAN, MICHIGAN
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Schematic Diagram
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Specifications and
Instructions
RME Model DB23
Preselector
The DB23 preselector is a low-noise, radio-frequency amplifier which can be
used to substantially improve receiver performance on the following amateur
radio bands:
3.5 mc to 4.0 mc
7.0 me to 7.3 mc
14.0 me to 14.5 me
21.0 me to 21,5 mc
26.0 mc to 30.0 mc
The DB23 consists of one tuned input circuit, which matches input impedance
of 75 ohms unbalanced or 300 ohms balanced, followed by two stages of low-
noise, neutralized, broadband push-pull 6J6 amplifiers. Finally, a push-pull 6J6
impedance matching stage delivers the amplified signal to the receiver with out-
put impedance of 150 ohms unbalanced or 300 ohms balanced. Input and out-
put impedance values actually encountered can differ within reasonable limits
without seriously affecting performance.
The voltage gain which can be expected from the DB23 varies somewhat with
the band in use and the output impedance selected (balanced output gives 6 db
more gain). Minimum gain, using a balanced output connection, will be about
26 db, while maximum gain, using the same output circuit, will be around
35 db. The tuned circuit in the DB23 adds selectivity to the receiving system
The amount of image rejection due to the-DB23 varies with the frequency, and
can be as high as 30 db on the lower frequencies.
Because the DB23 is a low-noise device, an improvement in signal plus noise-to-
noise ratio (or usable gain) is experienced. This feature is quite pronounced
with the less sensitive receivers, but even the better receivers will benefit. An
improvement of 7.5 db in signal plus noise-to-noise ratio is not unusual,
SPECIFICATIONS
Tubes: V1 6J6 R.F. amplifier
V2 6J6 R.F. amplifier
V3 6J6 R.F. impedance matching amplifier
Power Supply: Self contained; uses transformer and selenium rectifier
Input Impedance: 75 ohms unbalanced
300 ohms balanced
t Impedance: 150 ohms unbalanced
300 ohms balanced
Gain: 30 db (average)
Frequency Range: 3.5 to 4.0 mc; 7 to 7.3 mc; 14 to 14.5 me;
21 to 21.5 mc; 26 to 30 me.
Size: 7% in. wide x 6 in. deep x 5 in. high
Weight: 64 Ib, shipping

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Sleche Voice Specifications and Instructions / RME Model DB23 Preselector
‘The voltage chart below is for reference
when servicing:
Band Switch Band Switch
in 40M in 80M
Position Position
V1 pin 1 78 volts 40 volts
V1 pin 2 78 40
Vi pin 7 50 20
V2 pin 1 78 40
V2 pin 2 78 40
V2 pin 7 50 20
V3 pin 1 90 44
V3 pin 2 90 44
V3 pin 7 65 25
46
At Rect, Filter 110
All voltages measured to ground with a
20,000 ohm-per-volt meter and are positive.
Voltage Chart
Warranty
TLECTRO-VOICE, INC. worrsnts sach sew ipredutt imemutectored
to be free from defective mate
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Ribas) itor bor Wo "turned, transportation ea ‘within
ninety 190) days from the date of eriginal purchase by the
through sur authorized decler from who
nished by us. Accessori
this product are not cov
by this warranty.
This waranty Is in tlew of all other werrantis
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for us ony ef
of our product.
INSTRUCTIONS FOR SET-UP AND OPERATION
SWITCHES—The switching arrangement in the DB23 permits connection of the
antenna to the preselector or directly through to the receiver when the use of
the preselector is not desired. The input and output terminals of the DB23 are
coded for proper operation of this feature. The input terminals are marked
IN 1, IN 2, and G (ground), while the output terminals are marked OUT 1,
OUT 2, and G. Terminal IN 1 will be connected to terminal OUT 1 and ter-
minal IN 2 will be connected to terminal OUT 2 when the bandswitch is in the
“THRU” position. Therefore, when using an unbalanced antenna, it is impor-
tant to use a paired set of terminals i.e., for an antenna input of IN 1 and G,
the output should be taken from terminals OUT 1 and G. If a balanced antenna
connection is used (terminals IN 1 and IN 2), it is important to use a balanced
receiver input connection for a proper antenna match when the DB23 is set to
the "THRU" position. Finally, the DB23 will permit the use of a balanced an-
tenna system into an unbalanced receiver input, or vice versa, but it should be
remembered that this will result in unbalance of either the antenna or receiver
input when the bandswitch is in the "THRU" position.
Because the DB23 is an amplifier, incorrect n may result in a part of
its output being fed back into the input circuits with regeneration or active
oscillation resulting. Therefore, care must be exercised in installing the DB23,
‘ound between the DB23 and the receiver chassis
result in a very stable system. Precautions wi
INSTALLATION —
1, Connect line cord to 117 V, 50-60 cycle power source.
2. Connect antenna to proper input terminals on DB23 (see paragraph on
switches). For 75-ohm unbalanced input use terminals IN 1 and G, or
IN 2 and G. For 300-ohm balanced input use terminals IN 1 and IN 2.
3. Connect output of DB23 to receiver. For 150-ohm unbalanced output use
terminals OUT 1 and G or OUT 2 and G (note if IN 1 and G are used,
select OUT 1 and G). For 300-ohm balanced output use terminals OUT 1
and OUT 2. Use a short length of coax or a twisted pair for unbalanced
output. For balanced output a twisted pair or 300-ohm twin lead is suit-
able.
4. Provide a good ground between the DB23 and the receiver.
OPERATION —
1. Turn the "ON-OFF" switch (lower right) to the “ON” position. The
dial light should be illuminated indicating the presence of power.
2. Turn the band selector switch (center) to the desired frequency band.
3. Tune receiver to desired frequency.
4. Adjust peaking knob (lower left) for maximum signal. Peaking adjust-
ment should be made each time the frequency is appreciably changed.
Two positions of the peaking control may produce a peak in background
noise. This is due to image response of the receiver. Always tune peaking
knob to most counter-clockwise peak.
MAINTENANCE—The DB23 should require little maintenance. There are two
basic adjustments which may be made:
1, Trimmers on the tuning condenser (C1) which are used to trim the input
circuits to the proper frequency coverage. These need only be checked if
coils are replaced. They are adjusted to give proper frequency coverage
on the 3.5 to 4.0-mc band.
2. The neutralizing condensers (twisted wires C3, C4, C7, and C8) are used
to keep the triode stages from oscillating. Should oscillations occur, first
check the antenna and receiver connections as_well as the bond of the
DB23 chassis to the receiver chassis. If oscillation persists, remove the
DB23 from its cabinet by removing the knobs and the rubber feet on the
bottom. Then, adjust each twisted wire condenser by twisting unzil oscil-
lation stops. Finally, check each band of frequencies and readjust twisted
wire condensers if necessary. Usually one adjustment on the 26 to 30-mc
band is sufficient (new tubes are the most likely cause for adjustment).
RADIO MFG. ENGINEERS DIVISION
&
ELECTRO-VOICE,
INC.
|
BUCHANAN,
MICHIGAN
Part No. 53144
Printed in U.S. A.

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Schematic Diagram