Ferrograph 632 Service Manual

Page 2

FERROGRAPH

MODELS 632. 634 81 632H

SUPPLEMENTARY
NOTES
with
Revised Circuit Details
Serial No. 6/50.000 onwards

Page 55

APPENDIX I!

COMPONENTS LIST FOR MODELS .3211 AND MU (WV, 80 c,-a)

cmcmr
m vuva unuo TOL. uncannou mn- nos.

R1 2201: 1) w 521;, Carbon 1291913
R2 MK 11 27w Vitreous Enamel RF 1281918
R3 IM 1! w 209., Carbon 81'12863 ,R
R4 I-SK 11 w 5",. High Stability 31'128231R
R5 IODK u [w 57. High Stabdlity DP 1285011!
R6 1M u [w 209;. Carbon BP12863 18
R7 1K u w 5",; Carbon 11112908 (R
R8 270K 11 w 5" Carbon RP1285518
R9 220K u {w 5",. Carbon BP129191R

R10 250K u Dual Carbon PM.
(with R31) 1111243611
R11 ISOK 1.1 [w 5'31, Carbon 11912853112
R12 82K 1: 1w 5'32. Carbon 1281811!

R13 500K 11 Dual Carbon Pm.
(whh R39) 311243811
R14 Iron u w 5% Carbon RP 12853111
R1 5 100K 1) w 30% Carbon 191235211!
R16 47K u w 20% Orbon BP123491R
R18 1-8K :1 [II '31:, Carbon BP129171'R
R19 1M 1: [w 20% Carbon BP128631R
320 8-2K 11 [w 5% Carbon BP128381R
R21 lKu w 5! Carbon 1!? 290811!
R22 22K 11 :w 109:: Carbon BP:29131R
823 417K 11 [w 1021. Carbon 1912331 1R
R24 100K 11 III 20%;, Carbon BP128M1R
R25 1M 11 [w 20% Carbon BP128631R

R26 'IM 11 sum a Work-
R27 471: 1: w 20% Carbon BP12M91R
R28 10M 11 M 20%;, Carbon 3112866111
R29 1K1! Carbon lor. 311243911
R30 1M 11 {w 20% Carbon BP128631R
R31 R n {W 93;, High Srabil1ry BP128231R
R32 100K n {w 911, High Stability BP128501R
:33 11.»: u M 20";, Cnbon BP128631R
34 1 u w 5"; Carbon 1!? '2908 'R
R 270K 11 :10 511: Carbon BP128551R
R36 220K u [a1 93;, Carbon 31129191R

Page 56

Appandix B-mrbmtd

CIRCUII
m. vawa ammo 10L nonunion mt Mos.
R37 250K u Dual Carbon Pot.
(with R10) 8912-1361?
R38 150K 11 iv 5: Carbon 81'1 ,iR
R39 500K 1.) Dual Carbon Pal.
mo [50K | 5 Exam 8152418)?
1] U! "u l' 313'235311
R41 100K 11 [w 209., Carbon 31' 12852 ,R
R42 61K 11 [w 209., Carbon 39.62841!!!
:44 15K 11 [w 5'! Carbon Bl'.'2931.'R
49 1 u [w 209. Carbon BP.I'2863.IR
R46 8-2K u |w 59;. Carbon 13? 1231311!
R47 1K 11 lw 59.. Carbon BP 12908 :R
R48 22K 11 lw 109;. Carbon 111 12918 .'R
R49 11! N 59.. High Stability 111:er
R50 330K [1 1w 5";. High Stability BP.2963.'R
RSI 220K u {w 59.. High Stability 111 .2903 .R
RS2 250K 11 Im-Sn Carbon Pat. 811243511
R53 IOM u w 20.". Carbon 31'12866 :1!
R54 2901: u Rte-Sn Carbon Pal. 3152435,?
R55 220K u w S., Carbon 81' ;'29l9 .'R
RS6 5001(1) Dual Carbon lal.
(with R68) Bl'iZ-BBII
RS7 290K u Pre-Scr Carbon Par. 3912435,?
1;: 3321; w 20".. (20:: 31' {211-15 .R
v u [w 202.. RP 12883,!!!
R60 47K 11 [w 20?; Carbon 3912849,!!!
R61 [R 11 [at 55. H1311 Stability 81' .2964 ,R
862 310K 11 [w 93., High Stabiliry Bl' £2963 .11!
R63 220K 11 [at 5'3. H1311 Stability Bl';'2903,v'R
R64 250K 11 Pro-Set Carbon M. Lin. H.124)?
R65 10M u [w 20" ;. Carbon 81' 12866 .»R
R66 2501) I'm-8:1 Carbon Pat. Lin. 111 12415:?
R67 220K u w 59.. Carbon 111 .'2919.'R
R68 5001(1) Dual Carbon Pot.
(with R56) 111 12-13! .P
R69 250K I: Pra-Scr Carbon l'ar. Lin. Bl £26391?
R70 33K :1 N 209.. Carbon 31' 12845 .R

55

Page 72

accenoriet, having a graded characterittic with 1.700 ohm muimurtt value and having
an open circuit petition at'ler- thin. The potmtiomela ahould be wired to one of the thick
pine and to both the thin pint (linked together). when it is thut controlling both blot and
erase supplier to the heads.

With the potentiometer in the open circuit position no emote taltea place and the
original aignal it unallected. If the potentiometer it rotated tlowly the misunce gradually
Mia and the clue voltage lncreatea correspondingly. The eraaure alto increatet and with
the tape running. the original aignal it gradually faded out. When the miaunce it zero.
the crane and hint are at their normal values and recording can commence. Mlerwardn the
procedure can be reversed and the original aignal faded heck in. This method can also
be uaed to fade in and out at the end: ofa recording.

It will be found that even the above graded potentiometer dot-t not produce the tame
efl'ect aa a fade made during the recording because the crate field will lint selectively
eraae the higher frequencies (almllar' to the bias). Thin produce: the phenomenon that
the tignal tenda to grow mullled before an audible change in volume can be detected.
and it is advisable to produce the fade during the recording proceau if thia in practicable.
This eflect also tend: to produce an uppamt lump in the tlgnal on fint ttarting to turn
from the oil" petition to the maximum retittance position. The instantaneous change
from infinite red-lance to L700 ohma producer a very alight lump in the emote ol'normal
liequenclet but a much larger one It the higher frequencies.

Thi- ean be avoided by using two potentiometera, the L700 ohm special potentio-
meter connected between the pt'm oi the "Erase Only" plug and the IOOK ohm carbon
potentiometer acroaa the Biat Only" plug at tuggeated in Section 7.1. (In thin care no
link it required between the two plug! an the his and erute are controlled aepararely).
With both controla fully "oil", the "Bill" potentiometer ahould be turned Ilovvly till
the bias in fully on" and the high frequenclea have been faded gradually out. The
"Erase" potentiometer on then be turned till the desired level of erasure oeeurt.

Thi- laat arrangement can be very venetile and allover ruperlrnpoaltion to occur
over 0th cured or partially crued aignall. and u the retultant receding on the tape can
be monitored IImOII immediately. the tignal level: can be controlled to exactly the eflect
required.

It mutt again he emphaaited that the "Bin only" and "Eraae Only" plugs rnutt not
be removed when on "Record" and thin appliea equally to the potentlometett when
plugged into these tame aoclteu.

a. VOLTAGE SELECTOR (240V Modela only)

The voltage aeleetor llluttrated in Fig. I. hat been tuperaeded by twin voltage aelecton,
both knobt having three positions for maina auppliet of 200-2I0. 220-230. and 240.250 volta.
To telect the correct acttlng. both ltnobt thould be pulled outward: (they will not come entirely
free). rotated till the correct range is opposite the indicator atud. then pushed firmly home.

The voltage telector ltnobt mutt alwayt be set to the tame voltage range. otherwise excessive
hunt will teattlt.