1 튜브 리플렉스

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http://www.webex.net/~skywaves/homebrew/Homebrew_Projects.htm

12-volt 1-tube Reflex Receiver:

    I was so encouraged by the success of the simple regenerative set that I undertook the design of a much more elaborate one-tube set using a "reflex" circuit.  In this receiver the signal passes through the tube twice:  first, as radio frequencies and then a second time, as audio.  Because there is considerable RF gain before the detector, this radio is far more sensitive than a simple regenerative set.

    This is not a project for beginners.  The design employs a lot of hard-to-get and potentially expensive parts, almost enough to build a rudimentary superheterodyne.  You'll probably need a sweep generator to get the tunable band-pass filter working correctly.  You should be prepared to reengineer the circuit to suit the parts on hand.

The signals from the antenna pass through a double-tuned band-pass filter consisting of T1 and T2 tuned by a dual-section variable capacitor.  L1 provides negative mutual inductance between the two tuned circuits to maintain a constant bandwidth of approximately 12KHz across the entire 530 to 1700KHz tuning range.

    The secondary of  T2 applies the RF signal to the signal grid of the 12DZ6.  Amplified RF on the plate of the tube passes through a fixed 500-1700KHz band-pass filter consisting of two 2.5mH inductors and an 18pF capacitor and is applied to the 1N34 detector.

    The audio output of the detector is low-pass filtered by a 0.001uF cap to remove residual RF and is applied to the primary of the first audio transformer via the 100K-ohm volume control.  (Yes, the radio is sufficiently "hot" to need a volume control.)  The transformer provides voltage gain for the audio signal and additional rejection of RF present in the detector output.  A 15K resistor bypassed by a 1uF cap in the ground return of the transformer primary ensures that the detector sees a proper DC load under all circumstances to avoid audio distortion.

    Audio from the first AF transformer secondary is applied to the grid of the tube through the secondary of  T2.  Amplified audio on the plate of the tube passes easily through the 2.5mH RF choke and is applied to the primary of the audio output transformer.  A 300-ohm secondary impedance was chosen to match an available sound-powered headset to achieve maximum possible acoustic output.  This elaboration proved to be overkill.

    The 12DZ6 and similar tubes provide much greater gain than was available from the early triodes used in vintage reflex sets.  Therefore, a lot of attention needs to be paid to careful grounding and shielding and proper design of the various filter and bypass circuits in order to avoid oscillation.  If this radio whistles like a regen, it's not working properly.

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http://www.du.edu/%7Eetuttle/electron/elect27.htm

Battery Tubes

In the early days, nearly all radios (and other electronic apparatus) were powered by batteries, usually primary cells. With the rise of central power distribution, apparatus could be powered (and storage batteries charged) from the AC line, which was a practically unlimited, cheap source so far as radios were concerned. Transformers made high-voltage power supplies easy to build. Low-voltage filaments were largely replaced by 6.3V heaters and unipotential cathodes since power was now cheap. However, there still remained a demand for portable radios beyond the reach of power lines, and these were necessarily powered from batteries. The emphasis here had to be on small power drain, since battery power is expensive. Typical batteries were 1.5V and 3.0 V for filaments ("A" batteries), and 45V or 90V for plate supplies ("B" batteries), both the usual Leclanche "dry" cells. Filaments were generally used, because of their much greater efficiency in mA per watt. Typical battery tubes had filaments taking only 50 mA at 1.4V, only 70 mW. Plate currents were not high, since a few mA would be quite sufficient. For experiments with battery tubes, a D cell in a holder is an adequate filament supply, good for about 100 hours of service. Even an AA cell will do for experiments.

The 1LH4 is a loktal battery triode, which is shown in a voltage amplifier at the left. A similar octal tube is the 1H5-GT, and either will do in this experiment (but the basing is different!). A diode plate is included, connected to pin 4, and using the negative side of the filament as its cathode. The diode is not used in this circuit. The maximum plate voltage is 110V, but this can be exceeded a little in testing. I measured the characteristics for plate voltages of 125V and less, at grid voltages of 0.0, -0.5 and -1.0V (relative to the negative end of the filament). The plate current was always less than 1 mA. My results were μ = 62, g_m = 340 μS, and r_p = 182kΩ. These values are close to the published values. The characteristics are noticeably curved in this region, so the parameters will vary with plate current. The apparently low value of transconductance is quite reasonable for the small plate currents at which the tube is used.

The amplifier shown gave a voltage gain of G - -40, with an input of 0.4V peak-to-peak. The plate current was about 100 μA, which made the plate voltage 77V and the grid bias -0.26V. The bandwidth of the amplifier was quite good, roughly from 10Hz to 50kHz. It should be noted that the total power drain of this circuit is no more than 83 mW, of which most is the filament power. This is very economical for a normal-sized tube. The tube remains quite cool in service, incidentally.

A pentode voltage amplifier with a gain of about -33 is shown at the right, using a 1U5, a sharp-cutoff pentode which comes in a 7-pin miniature package. Note the polarity of the filament supply, which is important, since it supplies a little grid bias as well. Since the voltages and currents are low, you can use the same 1/4W resistors used with transistors. The capacitors must have an appropriate voltage rating, of course. The 10M resistor is a "grid leak" that will prevent the grid from going positive. It charges on the positive excursions of the grid to provide whatever bias is necessary. The plate current was 61 μA, and the screen grid current was 20 μA. The screen grid potential is above the plate's in this circuit. Pentodes offer the capacity for controlling the plate current through the screen voltage, so that the plate voltage can be what is required. For higher voltages, the screen grid is normally at the same or lower potential as the plate, on the average. The grid voltage cannot be measured accurately with a DMM or scope, since the bias conditions will be disturbed. However, you will find that the amplifier works very well. Measure the gain the usual way, with a function generator and oscilloscope.

Radios for motor cars had 6 V DC available, which was right for 6.3 V heaters, but could not be used for the B supply--even now, 6 V is inconveniently low for transistors. The usual solution was a vibrator supply. Contacts on the magnetically-driven vibrator armature converted 6 V DC to alternating current, which was stepped up by a transformer and then rectified to DC again (sometimes by contacts on the vibrator) for the B supply. Vibrators were electrically very noisy, and had short lives, but were widely used until solid-state equivalents became available. They came in cylindrical metal cans, and looked like electrolytic capacitors. The 0Z4, mentioned elsewhere, was a rectifer specifically for vibrator supplies. Another possibility was the dynamotor, a motor-generator with a single rotating armature and brushes, which could supply more power than a vibrator and was more reliable. However, they were too expensive for general commercial use, though widely used in the military.

When 12 V became the automotive standard, vibrator supplies or their solid-state equivalents, could still be used. Tubes with 12.6 V heaters were already common. Many had the heater center-tapped, so they could be used equally well on 6.3 V. However, 12 V is high enough to be used directly as the plate supply if the tubes are specially designed. A range of tubes was produced that could be used on 12 V only, without any high voltage at all. We have already discussed the 12DL8 and 12K5 space-charge-grid tetrodes, and how the space-charge grid allows larger plate currents for small plate voltages. There were approximately 15 tube types designed for 12V use, of which only three, the 12DL8, 12DS7 and 12K5 are space-charge grid tetrodes, behaving like triodes. The other tubes are of conventional construction, in general having low plate currents, less than 1 mA in many cases. These include twin-diode triodes (12AE6, 12FK6, 12AJ6), sharp cutoff pentodes (12AF6, 12BL6, 12CX6, 12EK6), remote cutoff pentodes (12CN5, 12DZ6), twin-diode remote cutoff pentode (12F8), pentagrid converter (12AD6), pentagrid (variable gain) amplifier 12EG6, and a twin-diode power screen-grid tetrode, 12J8. The last tube can deliver 20 mW output power, half of what the 12DL8 can do.

The 12EK6 (also known as 12DZ6 and 12EA6) is a screen-grid pentode for low-voltage use. A voltage amplifier using this tube is shown at the left. This tube was generally used as an IF or RF amplifier, so the load would have been a resonant circuit, not a resistor, giving much higher gain. However, the resistive load is easy to experiment with. There is no voltage to waste for cathode bias, so grid-leak bias is used. When a signal is applied, the bias will adjust itself so that the top of the input waveform is clamped to 0 V. Vary the input amplitude to verify this. This circuit works with an input of up to about 2 V peak-to-peak, perhaps best for an input of around 1.0 V p-p. The output voltage is then about 5.8 V p-p, the plate potential is 6.0 V, plate current 1.8 mA, and gain about -5.5, corresponding to a transconductance of 1.8 mS, about right from measurements of the characteristics and the position of the operating point in this case. The transfer characteristic is rather curved, leading to considerable distortion for larger amplitudes. Nevertheless, it is remarkable that the circuit works so well at such a low voltage.

As a triode (plate, suppressor and screen connected together), the 12EK6 has μ = 8.5, g_m = 6.3 mS and r_p = 1.35 kΩ. The transconductance varies considerably with plate current, which gives rise to distortion for large signal amplitudes.

These tubes make vacuum-tube experiments very easy without requiring high-voltage supplies, only what is found in a normal transistor lab.

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▒ 62 CORE 출력 트랜스포머

• 실리콘 Z-CORE 사용
• 62mm CORE 사용
• 가격 : \ 25,000/1개당

1차 임피던스	방식	출력	2차 임피던스
5KΩ	Single	12W	4Ω,8Ω,16Ω
5KΩ(UL 탭 있음)	Single	12W	4Ω,8Ω,16Ω
7KΩ	Single	12W	4Ω,8Ω,16Ω
7KΩ(UL 탭 있음)	Single	12W	4Ω,8Ω,16Ω
2.5KΩ, 5KΩ 7KΩ	Multi Single	12W	4Ω,8Ω,16Ω
4KΩ	Push Pull	15W	8Ω,16Ω
5KΩ	Push Pull	15W	8Ω,16Ω
7KΩ	Push Pull	15W	8Ω,16Ω
8KΩ	Push Pull	15W	8Ω,16Ω
10KΩ	Push Pull	15W	8Ω,16Ω
14KΩ	Push Pull	15W	8Ω,16Ω

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12EK6 12DZ6 12EA6

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