Revox G 36, Service Manual

Page: 15 / 52

Good high frequency response is possible only when the gaps of the record- and
playback heads are parallel to each other. Where recordings are to be exchanged for
replaying on other machines, it is furthermore essential that the head gaps are
accurately aligned to an angle of 90° against the direction of tape travel.
Correct adjustment is achieved by proceeding as follows:
- connect VTVM to the output of one channel
- run alignment tape and adjust nut 24 until a maximum reading is obtained from the
VTVM (observe the instructions included with the tape)
When correctly aligned, a sharp maximum will be indicated and the signal level must
drop when turning nut 24 in either direction.
Azimuth adjustment of record head
It is essential that the playback head has been aligned as outlined above.
- record 12 kc/s on good quality blank tape
- with the output coupled to a VTVM nut 24 of the record head should be
adjusted to give maximum output from the tape.
It is of little significance which of the two channels is used for carrying out the azi-
muth adjustment, however, it is advisable to check the performance of the other
channel also.
Head adjustment by the phase check method
The azimuth position of the head gap on stereo tape recorders influences not only the
signal level at high frequencies, it also effects the phase relation between channels.
The criterion of minimum phase deviation provides a more accurate indication of
correct gap angle than the adjustment for maximum output level.
To avoid a phase angle error of 90°, the azimuth should first get aligned by adjusting
for level maximum.
A simple method for adjusting phase can be seen from the diagram fig. 9. Both
channels are connected in parallel and azimuth adjustment is carried out at a test
frequency of 10 kc/s to give maximum output from the tape. Where a double beam
oscilloscope is available this should be employed so that traces from both channels
can be observed simultaneously. Accurate azimuth alignment will permit phase to be
maintained between channels at all frequencies, when correctly aligned a change of
frequency will not affect the locking of phase between channels.
To adjust the record head ensure that playback head is correct. Using the playback
channel as a measuring reference, a signal of 10 kc/s should be recorded and the
record head adjusted to give maximum playback output. Again the phase check
method may be employed and this will have the effect of phasing the machine from
input to output via tape at all frequencies.