jb7 signal tracer€¦ · tracer (continued) noise, intermittents, oscillation, whistles and all...

TRACER

(Continued)

noise, interm ittents, oscillation,whistles and all other faults areeasily located a t their source.

SPEC IFIC A TIO N S:— Size 17% ” long, 6 % ” deep, 7 % ” high. Front panel. Chromium plated brass with black engraved markings and let­tering.

CONTROLS AND INDICATORS ON PA N EL:— Main tuning dial for IF , OS and R F section approxi­mately five inches diameter tuned by large black knob approximately 2 1/i” diameter.

Pilot light on panel indicating tracer is in operation.

Main power switch marked off- on operated by black instrument knob.

Large plated earth terminal. De­tachable R F , OSC, IF probe.

Main wave change switch cover­ing short wave, broadcast, oscil­lator, and IF frequencies.

Channel selector switch which

changes tracer from IF and R F to oscillator.

R F gain control. Audio Volume control.

High and low output audio probe sockets.

Cathode ray indicator and switch. Self contained loud speaker on front panel.

An external power socket is also fitted on front panel.A Review of the Components used

The panel is thin—about 20 gauge and therefore requires some form of backing such as masonite or if you want the best, get a piece of Laminite sheet. This is an excellent material very sim ilar in appearance to the bakelite sheets we used on the front of early model radios. But it is much stronger, less liable to crack and has splendid insulation properties. However the insulation does not m atter on this panel as it is only the backing fo r a metal panel. The chassis is ready drilled and all valves except the power rectifier are mounted on a small separate chassis that is fitted on to the

main chassis by rubber mounting legs. The advantages of this are obvious to any radio man. At each end of the chassis is an angle mounting bracket that supports the front panels. The power trans­form er is a normal 80 mil upright mounting type sim ilar to that used on ordinary radios. The speaker is very important as most of your tests rely on the quality of it, so see that you get a good one. There are some terrible speakers on the m arket a t the present time. I t is possible to use a big speaker if you prefer it, but it would need to be mounted separately and 'would detract from the portability of the unit. The gang is a type H Stromberg Carlson two gang. The valves are all single ended types which are bedoming so in­creasingly popular these days, and all are octal base types except the magic eye which is a P base. The coils excepting the BC oscil­lator coil and SW oscillator coil which are standard receiver oscil­lator coils either Crown or R.C.S., are not normal types. The other

LOW AUDIO PROBE

6F6G 01 -QOS

high audio PROSE

0! AR0D5

CANC>\ r-jWAVE CHANCE 4 - swrrcH 2«5 ^

e y e s w it c h

H.T. CHOKE1500 n 20 WATT■ w --- ------------

SELECTO R .SWITCH

6 * 2.ioo v.

25C00V.0.

JB7 SIGNAL TRACER

jI

Note: The diode-triode in the top centre is a type 6SQ7, and requires a half-megohm resistor from diodes to earth,this having been omitted from the circuit drawing in error.

Page 12 The Australasian Radio World, November, 1947