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7.2Tape Speed Control
7.2.1 Using Frequency Meter or Counter.
Connect a frequency meter or counter to phono Output
and play back Tandberg test tape No. 11 (1.000 Hz) at
7 ll2 ips tape speed. Difference from correct tape speed
is indicated in %.
T o l er a nc e : 11 .7o
7.2.2 Using Transformer and Vacuum Tube Voltmeter
C onne c t a t r an sf o r mer 115/ 0. 5 V or 2 30/0 .5 V, 5 0 /60
Hz and a VTVM to the phono Output and the mains as
shown in fig. 7.1. Play back Tandberg test tape No. 10 a
(mains frequency 50 Hz) or No. 19 a (mains frequency
6 0 Hz ) a t 7 7 12 ip s t a pe s peed.
Deviation from correct tape speed will give a beat across
the VTVM.
Turn the Output Level Control to obtain
adequate meter deflection.
Clock the time for 10 comolete excursions of the meter
needle.
Read the speed deviation in per cent corresponding to
this particular time from the nomogram in |ig.7.2.
Brake left hand turntable slightly to decide if tape speed
is too high or too low. Increased deviation indicates too
low tape speed.
At 3314 ips, play Tandberg test tape No. 10 b (50 Hz
mains frequency). Proceed as for 7 1/2 ips to find speed
accuracy.
Speed tolerance:t l7o"
Fig. 7. 1
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50
60 66 excursrons-
F\9.7 .2
7.2.3 Using Tape of Known Length
Insert a tape of known length 450" (1144 cm) and play
it back. Time taken for the whole length strould be:
7 1/2 ips: 60 seconds
3 3 /4 i ps : 12 0 s ec onds
1 7/8 ips:240 seconds
Tnloranne
. 'l 7^
8 .0 A D JU S T M E NT O F T H E A MP L IF IE R S
WITH OU T T A N D B E R G T E S T T A P E S
8.1 Playback and Record Level Adjustment
Connect a VTVM to each output terminal. The signal
generator is connected to the Line Input of both
channels and tuned to 400 Hz.
The tape recorder is set up for stereo recording A-test, at
7 112 ips tape speed. Insert a good quality tape (Low
Noise).
Adjust the recording gain controls until the reading on
the output meters are 1.5 V with the playback controls
to maximum. Replace the VTVM for channel L with a
distortion rneter and depress the playback push button
(B-test). Adjust the recording current by R108 until the
reading shows 3 % distortion.
Replace the VTVM
for channel R with the distortion
meter and depress the push button playback R (B-test).
Adjust the recording current by R208 until the reading
shows 3 % distortion. Connect a VTVM to each output
terminal and proceed the recording as discribed above in
stereo B-test"
Adjust R150 (channet L) and R250 (channel R) until the
reading on the output meters are 1.5 V. Make sure that
the playback volume controls ate set to maximum.
Release the push-buttons
Playback L and R (Stereo
A-test) and check that the reading on the output meters
still are 1.5 V.
8.2 Record/Playback Curves
Connect a VTVM to each one of the phono outputs L
and R. In order to avoid interference from the oscillator
voltage, a band stop or a low pass filter tuned to 85.5
kHz must be inserted between the output and the
voltmeters.
Set the tape recorder for 3 314 ips stereo recording, level
30 dB below optimum (0 dB). Use the output VTVM
reading as reference levels.
Then record a 16.000 Hz signal at the same level and
check that the output voltage is within ! 2 dB. If the
voltage is too high, increase bias current by means of
R407 for channel L and R410 for channel R.
If the voltage is too low, alter the input signal frequency
to 1.000 Hz and adjust for maximum output voltage by
means of
R407
and R410
for
channels L and R
respectively. Then go back to 400 Hz, reestablish the
reference level, and recheck the output level at frequen'
cies between 50 and 16.000 Hz do not deviate more than
t 2 dB from reference level.
Perform the same check for 7 112 tps at frequencies
between 40 and 20.000 Hz, and then finally check for
1 7/8 ips between 50 and 9.000 Hz. Ref. level 4OO Hz.
the output levels of the two channels should not at any
frequency differ by more than 3 dB.
8.3
Readjustment of
Recording Levels and
Indicators
For readjustments of recording levels and indicators ref.
paragraph 7.1.3 and ?.1.4.
8.4 Distortion
Ref. para. 7.1.6 for adjustment and control of distortion.
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50 or 60 Hz
1 15 V) 60 Hz
23 0V , 50H 2
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