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How to Build a Two-Stage Radio-Frequency Amplifier 59
Radio Broadcast Photograph
LOOKING UP FROM UNDER
The function of the bus bar as part of the circuit and as a supporting member is clear. The sockets are of the panel mounting type
battery is connected to the battery posts on the terminal board at the left of the amplifier (looking at the rear). From right to left, these posts are designated as follows:— negative filament, positive filament, positive B battery, grid output, negative filament output.
The posts on the right terminal strip are: — antenna and ground, from right to left. The B battery post is connected to the 90 volt terminal of the B battery. The other connections are made as shown in Fig. 5.
With the aid of the wavelength curve shown in Fig. 1 2, the approximate position of the dials may be ascertained for a desired wavelength
setting. Due to differences in winding the coils and wiring, this curve will not be accurate for every amplifier of this type which may be constructed.
It will be observed that the antenna coupler condenser will tune rather broadly in comparison to the other two.
The method of tuning the amplifier would be to set the antenna condenser dial at the desired setting, referring to the curve and then slowly rotate the other two simultaneously through a small arc at approximately the same setting. When the sharpest point has been obtained, retune the antenna condenser dial for a final setting.
LIST OF PARTS USED,
1 Panel 7 x 14 x j\ inches @ $1 .00 $ 1 .00
3 Hammarlund Variable Condensers .00037 mfd @ 4.75 14 25
2 Federal Panel Mounting Sockets @ 1.20 2.40
2 Bradleystats @ 1.85 3.70
3 Sickles Coil units
2 X-L Vario-densers @ 1 .00 2.00
3 Na-ald Super De-Luxe Dials @ 1.00 3 .00
Brass strip .50
Mounting screws — wire, etc .50
1 Double-circuit Carter Jack , 1.00
$28.35
When the coils are home-made the supplies necessary for their winding are as follows: — \ lb. No. 22 d.c.c. wire Bakelite or metal bushing supports Washers
Insulation strip, fibre, celluloid, etc. Screws and nuts