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Multi Band Regenerative Receiver (Vacuum Tube):
Description:
Tunes in the AM band from 670 KHZ to 1.7 MHZ and the short wave bands from 6.7 MHZ to 17 MHZ. This is a two tube regen or regenerative receiver: one 1T4 detector and one 3V4 audio amplifier. All of this is accomplished with two plug in RF coils. This circuit is highly selective and very sensitive, only requiring a short antenna of at about 4 to 20 feet. This receiver will challenge any superhetrodyne in it’s ability to pull in stations from around the world. The audio output is designed to drive 8 ohm earphones. It is not necessary to use high impedance ones. Total current draw from the 45 V battery is only 7mA. It also has an audio output jack for connecting to an audio amplifier.
How it Works:
L3 induces antenna signals up into L2. L1 provides positive feedback to increase sensitivity. R3 adjusts the amount of efficiency and should be adjusted just below the point where the entire circuit breaks into oscillation. The 3V4 amplifier not only amplifies the signal but through T1, matches it to the 8 ohm earphones. In summary,
The 1T4 detects the RF signal and The 3V4 amplifies the audio for the earphones. Besides driving the earphones, there is an Aux audio output jack for feeding the audio directly to an external audio amplifier. Advancing R3 to the point of full oscillation will allow the reception of SSB and CW signals.
Construction:
Cut two pieces of 1⁄2 inch oak for the two side panels. They should be 2 1⁄2 inches high by 4 3⁄4 inches deep. Also cut the front aluminum panel to 5 3⁄4 high by 6 3⁄4 wide. The main aluminum deck (chassis) is 5 3⁄4 deep by 6 3⁄4 wide. My aluminum was .030 thick. The RF coils are wound on 1 inch PVC (which is actually 1 5/16 inch in diameter).
Coil forms may be made by first mounting an old 8 pin tube base in a socket, in a vise and grinding it down to about 1/8 inch high with a belt sander. Then use epoxy to attach it to a piece of PVC tubing. After winding the coils, apply several coats of Krylon crystal clear acrylic spray paint. The high voltage battery is constructed from 5…nine volt batteries soldered in series, which produces the 45 Volts required for the plates of the tubes. Caution: Do NOT over heat the connections to the batteries, as this could cause them to burst. A single C cell 1.5 volt battery provides the voltage to activate the filaments of the tubes. Note that C1 and C2 were 365 pF variable capacitors, but have had a number of plates pulled out with needle nose pliers (see the parts list).
Trouble Shooting
(proper readings from typical points to ground):

1T4 plate voltage = 36V
Voltage at pin 3 of 1T4= 17V.
Pot R5 at midpoint… Audio = 40 mV to pin 6 of the 3V4
Total current drain from the 45V Battery= 7mA.


Parts List (use 1/2 watt resistors):
R1 1 Meg
R2 39K
R3 100 K Potentiometer
R4 47K
R5 2 Meg Potentiometer
R6 47K
C1 11-194 pF Variable (7 full plates)
C2 9-19 pF Variable (one ¾ inch diam. plate)
C3 100 pF
C4 .002 uF
C5 .01 uF
C6, C9 1 uF @ 100V
C7 .05 uF
C8 .22 uF
L1,2,3 Wound on same PVC form
T1 10K to 8 ohm Audio Transformer
Tubes: 1T4 and 3V4 (one each)
BP1 Dual Binding Post
J1 Sterio Audio Phone Jack
J2 RCA Audio Jack
Seven pin tube sockets (2)
C cell Battery Holder
D.P.D.T Toggle Switch
1.5V C Cell Battery
45 V Battery (five 9v batteries)
High Intensity LED
Oak Wood Sides 4 ¾ x 2 ½ x ½ (2)
.039 inch Al-Chasis 6 ¾ x 4 ¾
.039 inch Al-Front 6 ¾ x 5 ¾
.039 inch Al-Variable mount 2 ½ x 1
¾ inch long spacers for the variable mount (4)
.039 inch Al-Batt. clamp 2 ½ x 2 7/8 (bend)
½ inch rubber bumper feet (4)
Matt cardboard scale 3 ¼ x 2
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