Revox G 36, Руководство по обслуживанию

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Modifications effective from serial number:
48401 (Motor-control circuit) onwards
48701 (Transmission response of record amplifier)
Motor - control circuit
Changes in the circuit of the spooling motors were effected in order to improve the
performance during the start-mode under extreme ratios of the supply and feed loads.
The relay R. St. mentioned on page 3 which operates with a delayed release time, now
supplies the higher voltage during the start-mode to the right hand spooling motor
only. Perfect starts are thus assured even with small tape roll diameters
on both sides. In situations where the recorder has to be started with large tape roll
diameters on the right hand side, performance is improved by the fact
that the tension remains -constant on the left hand motor during the operating time of
the R.St. relay.
The relay R.St. is being actuated by a current pulse. It remains de-energised during all
other stages of operation. The condenser C 68 (250 mF) which receives
its charge from the 24 Volt supply, discharges through the R.St. relay when
depressing the play-button and the relay gets energised for 0,3 sec. approx., thereby
feeding a higher supply voltage to the right hand spooling motor for
that period of time.
Transmission response of record amplifier
As can be seen from figure 13, page 14, there is a considerable rise in the high
frequency response of the record amplifier. This response characteristic is
necessitated by the standardised replay equalisation, as well as by the type of tape
emulsion utilised for recording. The frequency response displays a peak around 30 kc
on machines up to the above mentioned serial number. In conjunction with the
extremely wide response characteristic of the record and replay amplifiers, this could
cause interferences due to overmodulation when recording programs derived from
carrier distribution systems with too high a residual RF component after de-
modulation. Furthermore, it was difficult to obtain precise readings with wow and
flutter meters employing square wave test signals.
With the insertion of an inverse feedback loop (V3 - C80, V4 - C79, respectively
10 mmf each) plus a reduction in value of the cathode by-pass capacitor (V3 - C17,
V4-Cll respectively, reduced from 0,015 to 0,012mf) The response peak could now be
lowered to 23 kc approx. The frequency response curve remains unaltered in the
portion of the audio band which is required for sound recording. The following values
of attenuation are thus obtained:
7 1/2 ips 3 3/4 ips
30kc - 8 db -11 db
38 kc -12 db - 13 db
which greatly eliminates the possibility of generating beat signals from ultra sonic
frequencies. Where stereo broadcasts are to be recorded, use of the REVOX-
multiplex filter will be essential, particularly when operating at the tape speed of 3 3/4
ips.