Ferrograph 2 A NH Owners Manual

Page 1

T H E M A :\ L} A I,

0} THE

F E R R C} {1} ii: A P I i

Page 2

IMPORTANT NOTICE

To achieve the lowest noise levels from tape recording equipment, it is
essential that the recording and reproducing heads be free from residual
magnetism. In other words, the heads should not be allowed to become
polarised.

Normally it is difficult under conventional operating conditions to bring
about this state of polarisation, and in any case in the Ferrograph means
are provided for automatically demagnetising the head after recording.
This is done by arranging for the supersonic oscillator current to die away
gradually in the head as the main selector switch is turned from the record
to the wind-back" position.

To take the fullest advantage of this feature, it is necessary that the main
selector switch be turned slowly and deliberately between these two
positions. If it is turned quickly there will be insufficient time for the
demagnetisation process to be completed, in which Case any permanent
magnetism which has been introduced will not be removed.

By careful operation of the recorder it is possible to ensure that con-
ditions favourable to the retention of permanent magnetism cannot possibly
arise. For instance, the recorder should never be switched to or from the
record position unless there is a properly connected plug in one of the
input sockets, or the gain control is at its zero setting. Moreover the instru-
ment should not be switched on at the mains in the record position.

If, notwithstanding these provisions, polarisation does occur and a noisy
background ensue, beyond the capacity of the automatic demagnetiser to
remove, it is possible to effect a slightly greater demagnetising effect by
turning the main selector switch to record with the instrument already
on at the mains, and then switching off the whole machine by the on/ofl
switch at the right hand side of the front panel. In this way a better die-
away characteristic is obtained. After a few seconds have elapsed the main
selector switch can be turned to the playback position, and the instrument
once again switched on.

For very severe cases of polarisation which have been caused by DC.
being passed through the head windings, or by the approach of magnetised
screwdrivers to the head, service establishments may adopt a further method
whereby the supersonic voltage to the head is initially increased to the full
erase voltage before the die~away is commenced. This is achieved by
temporarily bridging Tags 2 and 3 on the right hand side of the Tape-deck
and proceeding as above. The link of course must be removed after this
operation.

It is emphasised that this method should be used only by skilled service
engineers.

Page 7

FERROGRAPH
MAGNETIC TAPE RECORDER
MODEL 2A/N

OPERATING INSTRUCTIONS

FOREWORD.

The Ferrograph is a very versatile instrumentgits applications range
far and wide over the fields of science, education, entertainment and industry.
Moreover its simplicity of operation together with its high standard of
performance commends it equally to the technically unskilled for whom the
recording may be an end in itself, as to the engineer or professional recordist
for whom it may be a very important link in a complicated system.

This booklet in consequence must have regard to the widely differing
outlooks of all these users, if its object-to enable each to derive the
maximum possible benefit from the instrument in his chosen fieldiis to
be fulfilled. Much technical information is therefore unavoidable. At the
same time explanations in simple terms are necessary for the benefit of those
who have no great knowledge of the electronic art.

In all cases, however, the contents of the succeeding pages will repay
careful study as they deal not only with the possibilities of the Ferrograph
but also with its limitations. As in any well ordered scheme of things, a full
understanding of the one is equally as important as the other.

/§.<>

THE BRITISH FERROGRAPH RECORDER CO.
SLOANE STREET ' LONDON S.W.1.

131

LTD.

Page 12

F|G. 2.

2. T0 LOAD THE MACHINE.

First turn the selector switch on the deck itself to the Wind 0n position. This auto-
matically opens the tape gates under the head cover. Load the full reel of tape on the left hand
spindle, with the free end at the front and pointing to the right. The coating then should be
on the inside.

If Hublok reels are being used, observe carefully the method of attaching and detaching
them. The small projection shotnd be deflected in the direction of the arrow with the thumb
while the reel is being gripped at its rim by the fingers. Do not force the reel on or 03 without
first deflecting the release knob.

When the magazine reel is secured the free end of tape should be taken across and in front
of the empty spool on the right hand spindle and its end secured to the empty hub by the
special clip provided. This tape securing clip has two coloured portions. The red portion
should be depressed radially inwards and the free end of tape inserted in the green part. A
few turns of tape should then be wound around the hub in a counter-clockwise direction.
Then draw out more tape from the magazine reel to provide a loop which being held in both
hands (about 7 apart) may be dropped through the V slot in the head cover. (See Fig. 4).

6

Page 20

DIRECTION OF TAPE TWWEL
->

ERASE WIDm SIGNAL TRACK

OIO
<-

doc"

05'

TAPE
CENTRE LINE

250

FIG. 5 T DISPOSITION

(VIEWED mom BACK or TAPE)

2-5.0 OUTPUT HT. SMOOn-IED OUTPUT

EA 2TH.

OUTPUT VALVE

ANODE
esVHEATt-zn SUPPLY

I
I
I I or. EARNED
|

CONNECTiON FOR [5.0.
DEMUTING RESISTANCE

me 6 Aux. SOCKET wmwa,

o©

®O© NOTE '- WHEN UEING 2531 EXTERNAL.

® 0 SPEAKER AN OPEN CIRCUIT 91.05

G SHOULD BE NSEETED N I551.
POT JACK

n6 7 CONNECTION FOE 1.511
EXYERNAL SFEAKEE.

O

Page 43

18.5. Head Alignment.

As the recorder leaves the factory its recording head will have been aligned so that
its gap is accurately perpendicular to the plane of tape travel. This is carried out against
a master tape kept for the purpose. It is important insofar as it controls the degree to which
interchangeability of recordings between different machines is possible without
loss of high frequency response. For this reason the recording head should not be interfered
with. In practice it is the component lust likely to give trouble.

In cases where the derangement of its setting has been unavoidable its re-alignment
will require a test tape carrying a standard signal of high frequency. This is played back
and the head is adjusted on the 050 roller on which it seats by the 4 fixing screws until
a maximum output position is obtained. As the head gap is rocked from one side of the
perpendicular to the other, the high frequency output may pass through successive
maxima but it is of course the greatest of these which represents the position to be finally
adopted.

18.6. Checking the Entire Instrument.

The complete alignment of the recorder and the measurement of its performance
requires a great deal of test equipment. Much of this will not be in the hands of the normal
Service Engineer. In the following description, alternative methods of measuring the
various factors involved are given but it must be pointed out that in some cases these
will be little more than estimates, particularly in respect of distortion and wow.

18.6.1. Recording Level.

It is assumed that the tests of gain, etc. previously detailed have been carried
out. The next step is the checking of the recording level. By this is meant the
maximum signal which can be applied to the head network for a given amount of
distortion on playback. As the instruments leave the works this level will be set so
as to produce not more than 5% total distortion on peaks. The process is as follows :-

With the main selector switch turned to recor and the gain control at zero,
check that the bias voltage agrees with the stated value, which for the particular deck
is to be found on the small label on the plate under the flywheel. The bias can be
measured between Deck Tags 3 and 1 with a valve-voltmeter.

Adjust the recording level meter accurately to zero and inject a source of 400
cycles into Jack 1 at a level of approximately 10 my. Connect an A.C. voltmeter
and a wave analyser or distortion meter between Pins 3 and 7 on the auxiliary socket.
Then adjust the gain control until the recording level meter reads 8. Check that the
reading on the A.C. voltmeter is between approximately 18 and 25v.

Re-adiust the gain control until the level meter reads 6 and then record a short
length of tape at this level at 76 p.s. Stop the tape, making a suitable reference
signal or mark and then proceed to record another paSsage with the signal level
meter reading 7. Repeat the procedure at readings of 8 and 9.

Rewind to the start of the test signals and then playback into the wave analyser
or distortion meter. Measure the distortion obtained for each signal input level

38

Page 52

APPENDIX C
LIST OF COMPONENTS-FERROGRAPH MODEL 2A/NH.

The components for this model are exactly as for model ZA/N with the exception of
the equalizer components listed below.

CIRCUIT

REF. VALUE RATING DESCRIPTION TYPE N0.
R2 100K (2 %w Carbon

R3 4~7K (2 ;w Carbon

R4 3K £2 Wire Wound Potentiometer

R5 l-5K 1! {5w Carbon

R6 25K (2 Carbon Potentiometet

R50 2-2K Q gw Carbon

C3 * ~01 nF 350v

C4 -1 F 350v

C5 -05 uF 500v

C6 " 3400 pf Silver Mica

C7 -04 uF Bass lift cap

08 * .05 uF By-pass

C40 * ~02 F

L2 Treble boost inductor 728

Values asterisked are nominal only. Actual values are selected during setting up.

4 PIN PLUG
ATTACHED To DECK

lVIEWED FROM FREE
END or: ple)

P2 SW2

15/sse 7V2'/5ec

00 fl\ ~~~~~~ V
O

|_ ' 594m) ' ' I v
EQUALIZER ca 26
--u- 6

C7 r._| C40 0 SKQ'

C4.L W0 l

L2 2 _

CE) 4 PW SOCKET

E2 E3 ATTACHED 1b .

' EQUALIZEE J
Vl 4K. Elo an "v"

(meme)

EQUALIZATION FOR FEEROGRAPH MODEL 24NH

47