Ferrograph 4 S CON Owners Manual

Page 1

THE MANUAL

OF THE

FERRO GRAPH

Page 2

THE FERROGRAPH SERIES 4

Page 5

19. Testing and Alignment (continued)

1961. Recording Level 38
19.6.2. Bias Checking . 39
19.6.3. Wow" and Flutter 40
19.6.4. Frequency Response i 40
19.6.5. Hum Level i 41
19.6.6. Signal to Noise Ratio ' 42
20. Alternative Models 42
.21. Conversion of 4A to 48 42
MODEL 4A/CON
Appendix A. Operational Fault Analysis 52
Appendix B List of Components-Series 4 54
Appendix C NARTB Characteristic 59
AppendixD Accessories 59
Appendix E. Magnetic Sound Recording Tape, Spec W372/49 62
LIST OF DIAGRAMS AND PLATES
Description Fig. Page
Supply Panel 1 . 5
Loading the Machine 2 . 6
Controls 3 . 7
Tape Loading 4 . 9
Track Dispositions 5 . 14
Auxiliary Socket 1 Wiring 6 . 14
Auxiliary Socket 2 Wiring 7 . 14
Tape Splicing... 8 . 13
Frequency Response Cuive 7. p.s 9 . 18
Frequency Response Curve 3} p.s. 10 . 19
Loop Operation .. ll 22
Loading of Loop Cassette 12 23
Power Unit, Top View... 13 25
Power Unit, Underside View 14 26
Amplifier, Underside View 15 27
Amplifier, Top View 16 28
View of Underside of Deck 17 32
Head and Capstan Assembly . 18 33
Model 45. showmg Stereo Head in position 19 44
Circuit Diagram (Standard) . 20 43
Mounting Cut out for Series 4/CON 21 5o
Plates showing Steread Unit 22 61
Wearite Defluxer 23 . 51
Circuit Diagram (Series 4
with NARTB characteristic) 24 64

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A. The mechanical deck carrying the motors, heads, reels, etc.

B.

The power unit and oscillator.

C. The amplifier chassis containing the amplifier, monitor meter, etc.

The Mechanical Unit is the Wearite Tape-Deck". It is connected to the amplifier unit
by detachable plugs and soekets. Many noteworthy features are incorporated in it, and
simplicity ofoperation is one ofits chief characteristics. Among the facilities it provides are :-

1.

:

9°59.

A double track provision which allows double the amount of recorded material to be
stored on one reel without any cross talk or sacrifice in performance. This is possible
as it operates on only halfthe tape width at any one time.

Two running speeds-allowing yet a further doubling of playing time where the
frequency range permits.

Rapid wind-back and wind-on of tape.

An automatic stop switch cutting off the machine unattended at the end ofa reel during
recording or playing back.

An instantaneous stop and start of tape transit, preventing slurring.

A cueing indicator giving an index of tape consumed.

An ability to accept a continuous loop cassette in place of the standard reels.

A third head position. This is located after the combined record reproduce head.
Standard or stereo heads may be plugged in, and there is an adjusting screw for gap
alignment.

T125 Power Unit and Oscillator employing two valves is mounted on the floor ol'the cabinet
with its control panel accessible at the rear of the instrument.

The Amplifier which employs five valves is mounted together with its operating panel
along the front of the instrument.

In the amplifier too are several points worthy of mention at this stage, so that a rapid
appreciation of the scope of the instrument will be possible :--

Li

Two input sockets for accepting the signal to be recorded are provided, each a stage
apart in the amplifier, and for low and high level signals respectively.

Measurement of recording level before application to the tape is carried out by a special
peak reading valve-voltmeter which gives sudden transients their true reading, and
which allows the maximum possible signal to be impressed upon the tape without fear
of overloading or distortion.

While recording, the quality ofthe signal cannot be modified by the operator. Providing
therefore that the signal itself is good, a full frequency range recording will always be
made.

On playing back however, tone control of both the bass and treble ends ofthe response
is possible, and the frequency spectrum may be varied to suit individual tastes. The
level response position is easily set if this facility is not required.

The general performance of the instrument is such as to warrant playing back over
loudspeaker systems capable of rather better acoustical treatment than is possible
in the instruments own case. To this end a 15 ohm outlet has been provided for this

and other purposes.

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To adjust or check the frequency response of 75" p.s. afrequency swcep from
40 to 13,000 cycles at a reading of approximately 2 on the level meter should be
recorded. In the absence of a synchronous continuous sweep it will probably be
necessary to carry this out in short independent steps carefully noting the frequency
at each point. (The low recording level is necessary to avoid overloading the tape
at the higher frequencies due to pre-emphasis.)

If now an A.C. meter or a valve-voltmeter having a level response over the band
in question is connected across a 15 ohm resistor plugged into Jack 3, the frequency
sweep may be played back and the various output levels noted. R4 should be adjusted
so that the valve-voltmeter shows the same output at 2,000 cycles as at 400. Then
R6 should be adjusted to keep the response level at the highest frequencies. If there
is a peak or dip for the curve around 6 to 9 Kc/s this may be taken out by making
C8 larger or smaller in value. At 375" p.s. the same procedure should be followed
except that the frequency range will necessarily be more restricted (40 to 6,000 cycles).
R5 will be found to affect frequencies between 1,000 and 2,000 cycles. The resonant
point at the upper end may be advanced or withdrawn by altering C3 on the speed
change switch panel.

19.6.5. Hum Level

If any major work has been carried out upon the amplifier or deck, the hum
level may be affected. The main factors controlling this are :-

A. The first valve of the replay chain.

B. The position of TR3.

C. The adjustment of the Mumetal wing on the playback head pressure arm.

Secondary factors affecting the hum may be :-
D. The second valve (this is the first valve of the recording chain and may cause
hum to be recorded).
E. The position of L2.
F. The position of the microphone matching transformer (if one is used).

G. The polarity of the mains input.

The presence of hum is most easily detected bv a sensitive meter, or a cathode
ray tube with an amplifier, connected across Pins 3 and 7 of auxiliary socket 1.
It can be controlled in some measure by the position of the mains transformer TR3
which is arranged so that it can be rotated for minimum hum pick-up on the sensitive
components. Any adjustment to it should be made while the motors on the deck
are running as this of course is the proper condition of playback.

Care should be taken to see that there is not too great a difference between the
readings with the motors running and with the motors stopped, as this will indicate
that hum bucking is taking place, i.e.that some hum is being injected in anti-phase

41

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4.5. Noise

4.5.1. Polarized Noise

The tape shall-be thoroughly erased by bulk erasing procedure in a 50 cycle
field. It shall then be played back over the standard head and amplifier of the previous
tests, but in this operation the playback head shall be subject to a polarizing field by
having D.C. passed through its winding while playback is taking place. A current
of2 m.a. shall be passed through the bias winding of the head via a limiting resistor
of not less than 12,000 ohms. The unweighted noise signal thus produced shall not
exceed 13 microvolts on tape which passes the requirements of Test 4.2.

4.5.2. Limiting Noise

For this test the playback amplifier shall be equalized so that with the particular
tape being tested an overall record /reproduce response, level within 3'; 3 DB from
70 to 9,000 cycles, is obtained when the recording network shown in Fig. 1 is modified
so as to include a 250 pf capacitor shunted across the 100K resistor to give a fixed
amount of pre-emphasis.

The reference level against which the noise is to be measured shall be that of
the maximum 400 cycle signal output giving a distortion not exceeding 5". After
this measurement the tape shall then be thoroughly erased by a 50 cycle bulk erasing
technique to give the best possible noise level and the playback head shall also be
thoroughly demagnetized.

The noise voltage of the tape shall then be measured as the increment in output
voltage from tape stopped, to tape running, when all components over 200 c.p.s.
up to the high frequency end of the band as stated above are included. The ratio of
noise output to maximum 5% distortion signal output shall be not less than 54 DB.

AFEGUARDS

lowithstanding acceptance under all the clauses above, the tape shall not exhibit any
ar characteristics either mechanical or electrical such as would cause its performance
nplete instruments to fall outside the overall instrument performance.

For Service Manual
5
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