United American Bosch Corp. 260 Schematic

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Manufacturer:United American Bosch Corp.

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Page 1:

PAGE L8 Bosca
MODEL 260,261
Stags Tube
Screen Cathode
Beet ? 80
Note These values are readings uf a high resistance voltmeter fx-cm sash socket
terminal to ground, with the exeeption of the filament voltages
are given for those tubes having the grid at ground The values are only approx
imate and will vary with the line voltage and the type of meter employed
IF PEAK 517.5 KC
rob mo.-0 meob
duo beams:
Cathode readings
E4 m , Egg
+ Elm = E = =

Page 2:

I. F. Ad ustment - The intenxedlate frequency amplifier is tuned to 517.5 K. C. With this fre-
quency supp from an approved standard signal generator, place the output terminals of the
generator on the input to the 8rd I. F. amplifier tube, 1. e. high side on the grid cap and lol '
side on ntal frame of receiver. Tune the adjustment screw of the diode transformer for nexium p
deflection of the output meter (connected across the voice coil terminals of the loud speakers).
A sensitivity of approximately 50,000 mics-ovolts should be indicated. Next, connect the signal
generator terminals to the 21111 I. F. tube. Tune the adjustment screws of the 8rd I. F. trans-
former for maximum deflection of the output meter. A sensitivity of 5,000 microvolts should be
indicated. Next, connect the signal generator to the lst I. F. tube and tune the adjustments of
the 2nd I, F. transformer for maximum. A sensitivity of 100 mlcrovolts should be indicated.
Next, connect the signal generator to the lst detector tube and tune the first I. F. transform-
er. A sensitivity of 10 microvolts should be indicated. Leaving signal generator on lst detec-
tbr, recheck all the I. F. stages.
R. F. Adgustment - (a) Broadcast Band
Check position of pointer to make sure lt is at the marking line just beyond
the 540 K. C. calibration mark wtnn variable condenser plates are fully engaged. Then adjust
set to the 1400 K, C. mark!-115 on scale. _Adjust signal generator to 1400 K. C. and connect its
output terminals througm a dummy antenna to antenna and ground connections. with about 1,000
miorovolts from signal generator (to make for ease of finding signal) adjust the 'oreadeaat os-
cillator trim condenser (B. 0. Osc. Coil - Trlmer) as indicated in Figure #L Reduce signal
generator input ce signal is tuned in so as to keep within a usehzl deflection of the output
meter. When signal ls tuned in, adjust the screws marked R. F. TRIIIEEIR and ANT-TRIMMER in Fig-
ure #L These last two need not be touched throughout further adjustments of the radio set.
Next, place the set at the 900 K. C. marking with signal generator likewise and adjust the screw
of the B. C. OSC. COIL LAGGING condenser until the signal is tuned ln. Return the pointer to
1400 K. C., the signal generator likewise. and mke the slight rsedjuetment of the B. C. 050.
TRIM condenser for good accuracy of calibration.
when all the adjustments as described are correctly made, the following eena
lltlvlty should be mintcined for a standard output of ICD millivatts on a carrier input modu-
rraqumay (nc) 1400 moo eco
Sensitivity (HY) 8 5 7
(b) Green Band (16% - SSG) K. C.)
By means of wevechange switch, place pointer on this band. Place pointer cn
5.5 nrt, set the signal generator to 5500 K. C. and with sufficient input to receiver from
standard signal generator, tune the screw adjus1ment labelled GREEN BAND TRIMER until the eig-
nal ls a maximm. Then place pointer to the 1.6110 mark, adjust signal generator to 1600 K. C.
and tune the screw marked GREEN BAND LAGGING CONDENSER until the signal output is a maximm.
Return set and signal generator to 5.5111 and readjust GREEN BAND TRIDMER the slight amount nee-
essary. check the sensitivity. '!'he`to1lourlng readings should obtain for 100 nllliwetts output.
Frequency QKC 8500 2400 1600
Sensitivity MV 5 5 S
NOTE. Each oscillator coil is provided with mans of adjusting its inductench Thi! BWP
s copper vane placed in the field of the cell and made movable by means of a screw adjustmenh
On the poem red and blue bands, the adjuetmnt my be made through holes in the side plate ad-
t t th' oscillator trimmer ccndansers While primarily o factory adjustmnt, these YBII
izyobe used for adjustment in the field where it has been found necessary to make r;p;;rs
oscillator coll. The method is as follows; Having gmc through the adjust c e
BAND as_ described abou, lt is found that the sensitivity, particularly in mid-scale (2.4 mega-
eycles) is not up to standard; say, for example, it indicates a sensitivity cf 20 mi?r?'Y?1%l>>

Page 3:

PAGE 5>>22 Boson C
Socket and
Trimmer Layout
Give the vane adjustment sores tvu turns in s elookwise direction and repeat the sdjustnxts
given shove st LEE. l.6l|>, and back to 5.5l|2. Then tune set end signal generator to 2400 LC.
end observe sensitivity. If this has improved, the sdjultnsut is in the oorreet direction and
a few more trials should be lids exactly ss described until the oorreot sensitivity is olrtsiued.
If on the other hand a peorersensitivity is obtained at 2400 K. C., return setting two turns te
its original position and repeat procedure making vans adjust in ocmmtereleokldee direotien, us,-
til correct sensitivity is obtsined.
It should *be Isntioned-again thnt this tedious procedure is never neeesssry
unless an oscillator coil has in some my becom danged. Inthe factory, special test equip-
ment is provided which makes for quick qdjustmeut of induetmees to the esrreet value betore the
coil is mounted in the radio set.
(e) ned Band (lbw - 9000 I. 0.)
Adjusiznents in this band ere nds exlotly ss described for the green band
except that the appropriate trimer end logging eendenssrs are used. In Figure #1, reference is
made to RED BAND TRIIMER and BED BAND LLGGIBG COKDEHSEL Sensitivity should be in the neighbor-
hood of 5 miorovolts across the sos1s._ _
(a) Brno nun (1o,ooo .- 20,000 x. c.)
Adjustments in this ben! should be made starting et tl: highest frequency
end, say 18 MJ if obtainable yn sigxal generator. A frequency not lower than 15 M! is desira-
ble. At this highest frequency, set pointer Un radio set to ollibrstiazi and tune BLUE BAND
TRIMMER until signal is correctly received. Then place the signal generator at 10 HJ and tune
radio set until signal is redeived. If this tuning point deviates tru the correct calibration
point, the vane regulating the osoillstu' coil lnductsnce my be reset and the tuning process
repeated until scale is adjusted to oolibretim md the correct sensitivity is obtained. Care
should be taken to ses that the adjustnsztt is made for the signal itself and not the Llp.
That ls, s 15 M1 signal should be tuned it st 15 ondial and its image, with more input from
standard signal generator, at 14 ll. Five lierovolts eoross scale corresponds to the oorreot

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