 | Construction plan for a
regenerative single circuit receiver. Diese
Seite in deutsch. |
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For b.c. band (MW), shortwave and LF (LW).
Last update: 08/08/2007
With this set of parts you can construct a radio set in great-grandmother style. Sitting in the medium-dark living room you can see the dark red glowing tube. Real nostalgia. Don't underestimate the reception performance of the set! Read below for more details. But you have more to handle in relation to a modern radio set: Change antenna connection, adjust the regenerative knob and the tuning knob and you have to live with the so called 'fading' because of the propagation during night (sky-wave reception) changes from time to time. But I think ALL THIS is the charm of this radio set.
You must have some experience with soldering,
you need also some tools like diagonal cutter and nipper and tweezer and
solder, different type of screw drivers and a drilling machine including drills
and a hack saw for shorting the plastic shaft of the potentiometer.
This is a set of parts but not a construction set, so it comes without any construction instruction, only the values of the parts (capacitors, resistors , coils turns list and so on) are part of the delivery. I offer the set of parts in two variants: With or without case. You can simply use a print out of this page as construction instruction.
| Description of the construction plan with
or without case:
Wires are only connected at the round dots. Other wire crossings are NOT connected. The capacitor C8 is only necessary when you use a magnetic earphone (approx 2000 ohms) instead of a crystal earphone. Using a crystal earphone shortens the C 8 capacitor with wire. C7 of version 1 is canceled. Construction strategy is subject to change. This set is a regenerative single circuit audion receiver. Because of this positive feedback (regeneration), the set has a good sensitivity and selectivity. Using this principle, the result is: During night perhaps you can hear in the upper part of the b.c. band some ghost signals of strong shortwave stations. This is a general problem of single circuit receivers. Better results with a wave trap (rejector circuit for short wave).
** = This type of earphone has a tendency to intermittents. Before you beginn to assemble read this notes:
You have to place the components, to mount, to solder, to drill. Best is a plastic case with the size of approx. length 25-30 cm, depth 15 cm, height 8 cm. Using Alkali-batteries of type AA, an operation time of 10-15 hours is possible. Alternativly you can use also NiCad or metal-hydride types (type AA). Because of the low current demand of the tube , you can use 9 volts batteries or accumulators. These 9 volts high tension-batteries will work much longer as the types AA. Take notice of the right polarity of the batteries. Solder the pins of the clips for the 9 volts batteries in series ( red to black. Red= plus, black = minus). Shorten the shaft of R1 to approx. 1.5 cm . The 3 banana jacks 'a,b,c' are connected to the cylinder-coils . There is a gap on the tube socket is between pins 1 and 7 . The employed tube EF98 is a special tube and works with very low high tension-battery voltages (12-18 volts) with good amplifying results. That is why this set needs only one tube. You can listen to local broadcast stations coming very loud and clear, distant stations with good volume. You can switch with S2 the capacity of the tuning capacitor C4 and C4a (with 1:3 gear). Are both sections in use, the result is a frequency range (in relation to the employed antenna) of approx. 510 to 950 kHz, with only one section 650 to 1700 khz. On short wave the second section is not in use. The frame of the tuning capacitor is connected to ground and the ceramic-isolated stator to point 'a' of the coils. Instead of the crystal earphone you can use an oldtime 2000 ohms magnetic earphone (read the notes about C8). Frequency ranges: 520 - 1650 kHz, 140 - 350 kHz (only in use in Europe and Asia), 2.5 - 13 Mhz. The coils for b.c. band, LF band, SW band: The construction of the coils is very simple! The windings are fixed with small strips of transparent adhesive tape (no holes for the ends of the coil wires needed). But when you are interested, you can construct a better coil form holder. Drill holes in the coil former for better fixing the coil leads. No problem, when your turns are wound not excactly turn by turn. But change not the turn direction of a-b and b-c.
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Notes for best operation: Wait 20 seconds after switching on. The filament of the tube is heating.... Best use an antenna wire length of 4 to 20 meters. Longer antennas result in less selectivity and the frequency range worsens. If you can use an outdoor antenna, please do so. A good ground is the (metal) water pipe or a (metal) central heating pipe. Do not use for antenna and ground the power line!!! Antenna connections: A1 for medium length antennas, A2 for short antennas, A3 for long antennas, A4 for short wave but also for very long b.c. band antennas. Connect in no case the antenna directly to the resonant circuit. Test the different antenna jacks for best results. Also when you change the band you have to reconnect the antenna for best operation. You have to readjust the positive feedback knob (regeneration) for each tuned station. Adjust to the point just before oscillating starts (squealing, jamming, distorted audio). During day time, but especially during night you can receive quite a number of stations (also long distance stations) on the b.c. band. Carefully juggling of the tuning knob and of the regeneration knob will provide a good result. Test the full band on different day and night times because that way you can receive most broadcast stations. During day time the longest distance is up to approx. 250 km, during night up to 2000 km, on short wave no limitations. LF-band (long wave) reception outside of Europe or Asia is difficult. By the way: Already on the first evening the set received in Berlin, Germany 55 stations from Europe and Asia and Africa on b.c. band , LF and SW only with a wire antenna length of 7 meters. The voltage of the heater battery may drop to approx. 4.1 volts before you have to replace the battery. You can use this set also for the modern Digital Radio Mondiale (DRM) in combination with a personal computer and a special software like DREAM. Details you will find on my Radiomann-Page .
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The glowing of the filament of the tube EF98
| Additional description of the construction plan including the case
(Take also notice of the above listed informtion.) The screws for the switches have a diameter of 2 mm, the other screws a diameter of 3 mm. The diameter of the mounting hole of the banana jacks is 8 mm, the potentiometer 10 mm. The hole for the tube socket 17 mm. The battery case (4* 1.5 volts) 'hovers' over the feed back pot on long screws.
** = This type of earphone has a tendency to intermittents.
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(C) Copyright: Rainer Steinfuehr, 2005, 2006, 2007 Berlin, Deutschland