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NOVEMBER, 1925
AN IMPROVED FIVE-TUBE RECEIVER
53
lower end of the plate coil in the radiofrequency tube circuit.
A tickler having variable coupling with the detector secondary provides regeneration. The grid leak condenser €4 is .00025 mfd., shunted by a grid leak of 2 megohms. The value of the grid leak will vary with the particular detector tube used.
Low ratio audio-frequency transformers of the latest design, having large iron cores upon which are wound large coils, should be used. This sort of transformer gives equal response on all the audio frequencies, insuring good quality of signal.
The unusual system of parallel tube amplification is practically new to the radio broadcast field, and is intended for the prevention of overloading in the last audio amplifier.
Two major controls afford tuning over the entire broadcast range. These are the tuning condensers; the detector circuit is so designed that its tuning is slightly sharper than the antenna circuit. As previously explained, regeneration adds to the simplicity of tuning, and the control for the tickler coil is located in the top center of the panel.
FIG. 3
A clear representation of the method of supporting the coils, shelf, and brackets. The audio-frequency transformers are mounted at right angles to each other to minimize magnetic coupling effects
This improved five-tube receiver employs the following parts, others, similar,
can be selected from apparatus approved by RADIO BROADCAST: | i. 80
18.00
2 Condensers ooo5mfd (Hammarlund), @ $5.00 ea
10.00
2 Dials, 4 inch, Na-ald, @ $.75 ea
1.50
I Dial if inch Na-ald
.25
4 Ballast Resistances, Amperite, @$i.ioea
4-4°
. . 6.00
5 Sockets Na-ald @ $ 75 ea
3.75
Rheostat 25 ohms Carter
1 .00
65
1.25
.70
Grid Condenser ooo25mfd , Dubilier
.50
.40
.45
65
9-4°
$60.70
Tuned Radio
Frequency Amplifier X
Power Audio Frequency Amplifiei
o
A
45
67
B FIG 4
The circuit diagram of the final receiver differs slightly with the diagram here in that a separate antenna coil is provided in place of the autotransformer arrangement shown. This antenna coil has three leads, the two ends and a center tap which allows of correct adjustment of the antenna coupler with the particular length of antenna used. The values of the various apparatus employed are: Ci and C2= .0005 mfd.; C3 = .000032 mfd.; C4 = .00025 mfd.jCj = .002 mfd.; C6 = .006 mfd.; Ri = 25 ohms, R2, R3, R4, R$ = J-ampere filament ballast resistances; R6 = 2 meg; AFTi and AFT2 = 2 to i audio-frequency transformers. Note the parallel arrangement of the last two tubes. The neutralizing and primary windings of the r.f. coupler are indicated as a double-wound coil, but in reality it is a single-wound coil with a tap taken off the middle turn