Ferrograph 422 Owners Manual

Page 1

THE MANUAL

OF THE

FERROGRAPH

SERIES 420

THE F F. R ROG RAM | COMPANY LTD.

K4. HIKCKFRIARS ROAI) ' LONDON S.P.I.

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EERR( )GRAPH MAGNETIC TAPE RECORDER
SERIES +20

Page 29

switch to a different value for each tape speed. The signal is conducted to the head via

CH Ind SK-l. From Pl the signal is led ma I section of the main tape switch to the upper
track section of the record head X5.

(d) Meter circuit

Considering the meter circuit. the signal arrives, via R25 and C24. at the grid of the
first section of VS which is connected as a cathode folloqer to provide a low impedance
source for charging CIB. R25 is included so that, in conjunction with R26. the meter
sensitivity can be set correctly. From the cathode of Via the signal ll rectified by MRI
and charges the memoir capacitor C18, the resultant voltage (negative with respect to
chassis) being applied to the grid ol'VSh. The peak level meter proper Ml is a lrnA DC
full scale deflection backward tending mtlliamclcr 11:. the pointer is at the right hand side
{or zero current and deflects from right to left. VShis cathode biasedby the resistor nenroek
RZQ, R29 and am so that st urn signal input 1 m is passed through Ml. and the pointer
deflemfullscakwhichisuurkedasm Enuediustmemtothiszeromarkcanbc
made by R29, the meter zero potentiometer on the front noel. The arrival of a signal
atthetnputtoVScametanegatirevoltamtoappearatVSbgridneduecstheanode
current and deflects the meter pointer. An advantage of this method is that the meter
cannot be damaged by an excessive signal as the efl'ect is to reduce the current through it
to zero for apparent full scale. The meter sale. although having l0 arbitrary divisions. is
substantially linen from no to nine, and 8", designated ldditionally by a red line,
corresponds to peslt recording level. The man is illuminated by two miniature bulbs
which also serve a an indication that the equipment is switched on. the meter itself
however only operates on the record" position of the main switch. this is done by switch-
ing its HT supply on at the same tune as that for the oscillator.

(e) Erase and Bloa supplies, Oacfllutor

ThehiuuideruevolugeisgmentedbyadmbleniodeWIoatedoothepower
unit chassis. The circuit is that of a conventioml push pull oscillator with the primary
ofthe coil L4 tuned by capacitors C54, C46, C53 in series.0ne side ofthe secondary of
1.4 is moaned to chassis and the other (output) side goes via the erase link" SK? to
the track selection twitch SW9. The pole ofthe switch section to which it you also has
connected to it a variable resists: R86 marked bias equalise". The other end of this
resistor goes to anothuswiteh section which connects it tochassiain theupperorlower track
(am), but not in the stereo, position of the switch. The (main of R86 therefore is to
cornpemate forthe reduced load on the oscillator and maintain the bias voltageatilcorreet
value when ash track is recorded independently.

lnorder to avoid dimming current: leading tosorne degree of cross coupling. both
leadatothetuausedsectionoftheetueheadX4arediioottnectedwhenrecordingrinfle

track. ltwasfmmdnecersarythoughtodisconneet onlyoneladofthebiassupplyto
mmmamemwxs

3|

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APPENDIX B
mMIONENTS HST FOR MODEL U AND mu FERROGRAPIIS

alum ; [

m. mun nuns TOL Imam-non Mn Mos.
R1 1501(1) [w 20".. Cuban 3? 2927 R
R2 l-ZK 12 27v Viacom Enamel BP2819R
R3 [M u {w 20"., Cuban "52663.1!
R4 1R1! 1w 5".. High Subiliry RP -2964:R
R5 330R :1 1w 5".. High Stability 131 2963M
R6 10Mu [w W2. Cuban 131 2366.1!
R7 220K 1w 52. High Stability BP 29031
R8 330K 1! hr 10. Cuban 3? 286931!
R9 2201: 1: 1w 5,. Carbon BP.29|9 R
R10 250K 11 Dull Cuban Pot.

(with R37) 31 2436?
R11 330K u w 10.. Cuban 3? 2869611
R12 92K 12 11v 5",, Carbon 31 28381!
R13 500R 11 Dual Cuban Pub

(with R39) 81 2438,1
R14 231R 1: 1w 5".. Cuban 111 929193
R15 100R 1! w 20".. Cuban 111' 1285211
R16 47K 1: {w 20"., Cuban 1!? 2849 R
R17 '150K 1: Selccmd It Works
ms l-sKu 1w 5 Carbon BP 2937]!
R19 lM u [w 20".. Carbon 51 2863 11
R20 82!: n 1w 5"., Carbon 31 12638 11
R21 1R :1 1w 5"., Carbon B? m 5R
R22 22R :2 hr 10".. Carbon RP 291811

R23 4-11! 11 hr 10".. Carbon 31 2831 R
R24 1mm n [W 20' Cuban BP 2386 R
R25 1M1! 1w 5'2. Carbon 3? MR
R26 'IM 1) Selected n Womb
R27 47X :1 1w :0. Carbon BER R
R28 10M U w 20- Cuban 31 286641!
R29 1K1! Cuban For. 111 2437 P
R30 1M u [w 20"., Cuban 1132863 R
R31 K u w 5"" High Stability BP.2964 R
R32 330K u [w 5" High Stability 131 #2963 .R
R33 10M u ;w 20".. urban 13le R
R34 2201! {W 5",, High Subdin 3? 2903.11
R35 330R11 f {Iv 10"., urban "2869 R
R36 mm u 1i: ' 5",, Cuban 29 R