Bulova Watch Company C-751 Schematic

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Manufacturer:Bulova Watch Company

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Page 1:

Page 187-13


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Page >18 7-F


Never check voltages until all tubes are fully waned up to proper operating condition. 'he voltage
table given below is talnn at 115 volts line with a Model 547 Weston set checker. It walt be n-
umbered that the voltage readings taken vary directly el the lim voltage and also vim me accuracy
or the meters used. A variatim ef 105 plus or ninul il pomilsible. I

115 v. line Volume Control Pull 6m

Type e? Yeaition Iilsnent will* vogt PROM: A '53123
Tube ot Tube volts e a Ln'l . . \ o
255 Radio Frequency 2.4 240 2.15 8.75 ' 27
' ess Intermediate 2.4 25'1 2.15 2.'/5 \ 'zz
r ze. and Detector 2.4 100' 2.1' 2.5 ` as'
t an Pentnce 2.4 coo 16.5" 52.5 j :so

*Those readings are only comparative and are not true voltages applied. The volt unter, 'hon tha
reading! are taken at those points, lo in series with a very high resistance.

'* To road the 247 bias, read between H.K.s'pesker socket and ground.

IMMEQTE Eng" goalie ormers are or the band pass ty'pe and oi' exceptionally high uniform gain. They
are tuned to 175 kilocycles. The intermediate frequency trimers are lmunted on an ieolantito base,
preventing the transformer from becoming detunad due te the trimr condensate absorbing moisture or
warping. For this reason it should rarely, if ever, be necessary to :re-track t'he internsdiate
frequency trinmers. In the event that it should be advisable to ro-align1 the intermediate frequency
coils, it is absolutely essential that a 175 Kilccycle oscillator and an output measuring device be

Because of the construcuon and thorough impregnation oi' me intermadi ate` coils, the intermedi a"
stages abeuid rarely need m-tzeckicg. Only when an internsdiate coil has become defective due either
to an open oc' burned out winding, should it be necessary to re-adjust thai intermediate trims rs.
Should this occur it is necessary that an oscillator 'oe used md me intermediate trimers Be
adjusted at 175 kilocyclsa. Tc align the intermediate stages, connect tno high side oi' the oscillator
output to the grid circuit oi' the first detector, which is done by disconnecting the grid cap oi' the
2.24 first detector and connecting the high side of the test oscillatnr tolthe control grid oi' this
tube. The ground aide of the test oscillator should be connected to the ground poet on the chassis.
Set the oscillator at 175 kilodyclee and adjust the output or tln oscillator so mat a convenient
reading is obtained on the output meter. Be sure that the output from the oscillator is not so`

large that it will overload the second detector. If airing the aligimentl tha meter goes off scale,
reduce the output of the test oscillator or adjust the receiver volume control.

The trimme rs of the intermediate coils are accessible through the small holes in the tcp of the
intermediate nxield can. There are two trimmers to each intermediate coil. Align the grid trimmer
of the rirst intermediate coil. After a maximum reading is obtained by adjusting the grid trimee'
on the rirst int frmediato adjust the primary for maximum reading and than ro-check the grid side to
make certain the alignmnt or the secondary has not been changed by the adjustment ot the primary.
The same procedure ie followed in aligning tha second intermediate coils.` After both intermediate
coils are properly aligned the adjustment of the intermdiats stage is complete and they should not
be further disturbed. 1

Replace the grid cap on the first detector and annect the oscillator output leads to tin ants-nm
and ground posts ei' the receiver end set the o_ecillatm' at 1435 kilocyclep. Then tune the receiver
to 1455 kilocycles on the dial. It is important that the receiver be tuned to this point. It the
receiver is out of the cabinet it will he mcessary to use some tporsry? indicator eo that tho
position 1435 kilocyolee on the dial 'may be accurately located. (This irdi cator should be set ao
that when the variable condensate are at the maximum capacity stop the indicator points to the last
line on the dial at the low frequency and.) Then track tin variable condensere by ed usting tha
trimmer condenser! in the following order: Oscillator antmna ami radio frequency - reading ml
the front of the receiver toward the hack, the variable condenser sectionh are : Oscillator, antenna
; and radio frequency). After the variable condenecrs have been properly tracked at li55 kilocycles,
adjust the oscillator to 1295 kilocycloa. Tune the receiver to this frequency. Check aligzmnt
of the condensers at this point 'by bending thev end plate oi' the rotors ini and mt, noting the change
111 readme ?n the output meter. It when the plates are bent in the leading is increased, it is
an indication that that particular section requires mre capacity and the and plate should be pen
manently bent in at this point; or, it when the end plate is bent away, the reading is increased, the
end plate should he bent away permanently, aa it io an indication that that particular section
requires lese capacity at that partimlar point. The variable condenser.; should be checked in this
manner at 1295, 890, 650 and 550 kilocyoles. These points have been chosen so as to take advantage
of the slots in tb end plates of the variable condensere. This procedure of bending plates should
rarely be necessary on the oscillator section, as the plates et the oscillator section are es-
pecially designed to properly track over the broadcast spectrum, providing the antenna and radio
frequency stages are correctly aligned. 1

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