Northern Airborne Technology 250 - Manual (Page 12)

EQUIPMENT MANUAL 250-16-1
250/250-16-1 Page 3
All internal screwdriver potentiometer adjustments of the Model 250 are set to factory standards.
If it is necessary to change a setting, refer to the calibration and maintenance section of this
manual.
The amplifiers are adjusted for acceptable listening output levels into the proper loads with ADF
receiver inputs of 7.75 V
RMS
and PSC, TV, Stereo and Brief audio inputs of 1.00 V
RMS
. With the
volume controls set to maximum volume position, these inputs will provide 7.8 VRMS (28 watts)
into 2 ohms at each speaker output. The receiver input levels are realized when receivers are set
for 100 milliwatts into 600 ohms. If these levels are greatly exceeded at the inputs, the audio will
become distorted due to peak clipping and audio bleedthrough will be noticed. The amplifiers,
however, will not be damaged.
2.0 SPECIFICATIONS
Input specifications are expressed in volts RMS, rather than milliwatts, to avoid any
misunderstanding.
INPUTS:
ADF:
Two single, switched audio inputs for ADF, etc. Input level is 7.75 V
RMS
.
PSC:
One single, switched audio input compatible with the Pilot Select COMM
output of dB Systems cockpit audio control amplifiers such as Model 438
and 700 which provides a 1.00 V
RMS
signal produced from a summation of
selected COMM, DME, and MKR receivers.
TV:
One single, switched audio input for TV, etc. Input level is 1.00 V
RMS
.
STEREO LEFT:
One single, switched differential audio input for the left channel of stereo
audio from an AM/FM stereo receiver/tape or CD deck, etc. Input level is
maximum 1.00 V
RMS
(at maximum source volume) and audio LO is not
common to that of other inputs.
STEREO RIGHT:
Same as Stereo Left, switched by the same control input as Stereo Left.
BRIEF:
One single, switched audio input for briefer audio, etc. Input level is
1.00 V
RMS
.
PA MIC:
The microphone input, used for cabin paging audio, supplies bias current
and is compatible with carbon and amplified dynamic microphones.
PAGING VOLUME:
Controls level of PA MIC and Brief audio inputs to the PA Sidetone and Left
and Right Speaker outputs. Volume control range is 30 dB (minimum)
controlled by a 10,000 ohm, 1/2 Watt, linear pot. Maximum volume is with
maximum resistance.