Voltase hobby

The quartz clocks which have dominated time-keeping for the past 20 years or so have one problem: their errors, although slight, are cumulative. After running for several months the errors can be significant. Sometimes you can correct these if you can slightly tweak the crystal frequency but otherwise you are forced to reset the clock at regular intervals. By contrast, mains-powered synchronous clocks are kept accurate by the 50Hz mains distribution system and they are very reliable, except of course, when a blackout occurs.

 This circuit converts a quartz clock to synchronous mains operation, so that you can have at least one clock in your home which shows the time. First, you need to obtain a quartz clock movement and disassemble it down to the PC board. For instructions on how to do this, see the article on a "Fast Clock For Railway Modellers" in the December 1996 issue of SILICON CHIP. Then isolate the two wires to the clock coil and solder two light duty insulated hookup wires to them (eg, two strands of rainbow cable). Drill a small hole in the clock case and pass the wires through them. Then reassemble the clock case.

This Digital Electronic Lock Circuit Diagram shown below uses 4 common logic ICs to allow controlling a relay by entering a 4 digit number on a keypad. The first 4 outputs from the CD4017 decade counter (pins 3,2,4,7) are gated together with 4 digits from a keypad so that as the keys are depressed in the correct order, the counter will advance. As each correct key is pressed, a low level appears at the output of the dual NAND gate producing a high level at the output of the 8 input NAND at pin 13.

Read : Cheap Bicycle Alarm Schematics Circuit

Digital Electronic Lock Circuit Diagram

 

The momentary high level from pin 13 activates a one shot circuit which applies an approximate 80 millisecond positive going pulse to the clock line (pin 14) of the decade counter which advances it one count on the rising edge.

Read : Emergency Light and Alarm Circuit Diagram

A second monostable, one shot circuit is used to generate an approximate 40 millisecond positive going pulse which is applied to the common point of the keypad so that the appropriate NAND gate will see two logic high levels when the correct key is pressed (one from the counter and the other from the key). The inverted clock pulse (negative going) at pin 12 of the 74C14 and the positive going keypad pulse at pin 6 are gated together using two diodes as an AND gate (shown in lower right corner).

Read : Burglar Alarm With Timed Shutoff Circuit Diagram

The output at the junction of the diodes will be positive in the event a wrong key is pressed and will reset the counter. When a correct key is pressed, outputs will be present from both monostable circuits (clock and keypad) causing the reset line to remain low and allowing the counter to advance. However, since the keypad pulse begins slightly before the clock, a 0.1uF capacitor is connected to the reset line to delay the reset until the inverted clock arrives.

Read : 5 Zone alarm Circuit Diagram

The values are not critical and various other timing schemes could be used but the clock signal should be slightly longer than the keypad pulse so that the clock signal can mask out the keypad and avoid resetting the counter in the event the clock pulse ends before the keypad pulse. The fifth output of the counter is on pin 10, so that after four correct key entries have been made, pin 10 will move to a high level and can be used to activate a relay, illuminate an LED, ect. At this point, the lock can be reset simply by pressing any key. The circuit can be extended with additional gates (one more CD4011) to accept up to a 8 digit code.

Read :  Alarm Control Keypad Circuit Diagram

The 4017 counting order is 3 2 4 7 10 1 5 6 9 11 so that the first 8 outputs are connected to the NAND gates and pin 9 would be used to drive the relay or light. The 4 additional NAND gate outputs would connect to the 4 remaining inputs of the CD4068 (pins 9,10,11,12). The circuit will operate from 3 to 12 volts on 4000 series CMOS but only 6 volts or less if 74HC parts are used. The circuit draws very little current (about 165 microamps) so it could be powered for several months on 4 AA batteries assuming only intermittent use of the relay.

In the world of electronics, vacuum tubes are almost obsolete. Nearly the last holdout, the cathode ray tube (CRT), is rapidly being replaced by the LCD and other new technologies. Despite this trend, the vacuum tube has seen a big revival in the field of guitar amplifiers, and to a lesser extent, hi-fi amplifiers. Vacuum tubes and related parts have become more readily available in recent years as numerous companies have tapped into this market.

The reason for the popularity of tubes in guitar amps involves the nice tones that are produced when tubes are driven to the point of distortion. For some background on this, follow some of the links on The Strat Monger. There are numerous solid state "modeling amps" that try to simulate vacuum tube amps with digital signal processing (DSP) techniques, but in the end, that method is never more than a simulation. It just aint the same as the real thing.

One can spend a large amount of money and time building a tube amp from scratch. Hammond organ ampifiers chassis are available on the surplus market for a reasonable price, they make a good starting point for a guitar amp. The difficult job of cutting chassis holes for the tubes and transformers is already done, one just needs to drill a few holes for the potentiometers and connectors. This project started with the amplifier from a Hammond M2 organ, chassis model AO14-1B.

The output stage of this amplifier resembles a fusion between a Fender Princeton Reverb, Fender Vibroverb and ham radio transmitter. With 6V6 output tubes running at a 420V plate voltage, it puts out approximately 18 watts of audio power. The 17" reverb tank provides a deep echoey sound. The "simpler is better" philosophy was used in the design, multiple inputs with their own preamp stages were intentionally avoided to reduce hiss. The amp is plenty loud, and the sound quality is excellent. The Hammonator amp has worked well driving both 12" and 15" guitar speakers.

The Hammonator Model 1 amp is a simplified version of the Hammonator 2RVT circuit. Builders can start with the Model 1 circuit and easily add the Model 2RVT Vibrato/Tremolo circuitry at a later date.There are a few unique features in this amp, and some slight deviations from the aforementioned simplicity goal. An optional fluorescent EM87/6HU6 "magic eye" tube (EM87 in action) is used for an output level meter, it is fun to stare at while playing. The EM87 uses a peak reading circuit that was inspired by this design then modified somewhat. There is a reverb send control (Dwell) that can be used to expand the variety of reverb sounds. Most Fender amps send only a full-strength signal to the reverb spring. By turning the reverb send signal down a bit, a less "clangy" and more "spacey" reverb sound results.

The Hammonator also features a negative feedback control. With the feedback control turned all the way to the left (max negative feedback), the amp compresses the signal and the waveform peaks are reduced. With the feedback control turned all the way to the right, the sound is louder and less compressed and approaches that of the popular Fender Tweed Deluxe (5E3) amps. The feedback control could also be called "Clarity", "Gain" or "Presence".

This amp uses four octal base 6SN7 dual triode tubes for most of the low level signal amplification instead of the more common 12AX7 or 12AU7 tubes. This was done because the chassis was already set up for the octal sockets. Boutique amp enthusiasts will probably like this feature since the 6SN7 tubes are older and may have more of a vintage amp sound. Fortunately, the 6SN7 is still easy to acquire. This amp has been "tuned" for good sound, the bias settings of all of the tube stages were tweaked while a guitar was plugged in. This process was used to optimize the musical qualities of the amp. Not all vintage 6SN7 tubes are the same, quieter Sylvania tubes were used for VT1 and VT3 to reduce the hiss, nosier RCA and GE tubes were used elsewhere. You can test for noisy 6SN7 tubes by putting them in the VT1 socket, listening to the hiss level and tapping on the tube to listen for microphonics.

It is possible to change VT1, the first preamplifier and tone recovery tube, from a lower gain 6SN7 dual triode to a higher gain 6SL7 dual triode without any wiring changes. This allows the amplifier to work better with low output guitar pickups. This trick is often done with other amps by swapping 12AU7, 12AT7, 12AY7 and 12AX7 tubes, they all share the same pinout but have different gains.

The newer and more common AO-29 (M3 organ) chassis would also make a good chassis for a guitar amp conversion. The three 9 pin tube sockets could be used for 12AX7 or 12AU7 dual triode tubes and the five 7 pin tube sockets could be filled with common 6AV6 tubes (similar to a single 12AX7 triode) or 6C4 tubes (similar to a single 12AU7 triode). A similar circuit layout could be used on the AO-29 chassis but the cathode bias resistor values on the 7 and 9 pin preamp triodes would need to be changed from the values used on the 6SN7 tubes. The AO-29 power transformer and output transformer are very similar to those used in the AO-14.

Connections:
Power Input - grounded 120VAC
Guitar Input - High Impedance
Reverb Send
Reverb Return
Speaker Output - 8 ohms

Controls:
On/Off (on the back)
Input Volume
Bass
Treble
Reverb Send (Dwell)
Reverb Return
Feedback (Gain)

Theory:
The AC power input circuitry was modified from the original Hammond circuit. The power transformer is old enough that it was designed to run on 110V-115V mains instead of the 120V mains found today. Running the stock amp on 120V produces higher filament and B+ voltages, the higher filament voltages can shorten the life of the tubes. This problem can be easily fixed by putting the 5V rectifier filament winding in series with the AC primary winding. The 5V phasing must be correct, the easy way to test this is to try both orientations and monitor the 6.3V filament winding, use the lower wiring that produces the lower voltage. When the tubes are plugged, the filament voltage should be very close to 6.3V.

A grounded plug was used, this is critical for safety. A 2 amp fuse and switch are used to provide a standard fused disconnect. The varistor on the transformer primary protects against line voltage transients, those can get multiplied on the high voltage output winding and cause damage.

The transformer high voltage winding is sent to a center tapped full wave rectifier consisting of two 1N4007 diodes. The high voltage DC is dropped through a typical chain of resistors and capacitors to produce the voltages used in the amp. The first resistor (150 ohms/2 Watt) is used to set the initial B1+ voltage that drives the power output tubes.

There is a lot of misinformation on the net about tube rectifiers vs solid state rectifiers and the effect on amp sound. This probably derives from the more efficient nature of solid state diodes and the resulting higher voltage when a direct substitution is done. Putting a resistor after the diodes drops the B+ voltage to a level that is closer to that achieved with a 5U4 rectifier. The diodes have the advantage of better efficiency due to the lack of a high power filament, the power transformer will also run cooler using diodes. The 1nF/1KV capacitors across the diodes protect against high voltage transients and eliminate RF rectification issues.

The 5H inductor choke is used to reduce hum in the preamp stages, the value is not especially critical. The 220nF capacitors in the power supply are fairly unique to this design, they improve the high frequency response of the amp. This is a trick that was borrowed from solid state circuitry. If you dont have any 220nF caps, 100nF caps should do the job.

The Vbias- negative voltage is derived from a half wave rectifier and a resistive ladder. The 25K bias control can be adjusted to set the idle bias level on the power tubes. Bias levels for both 6V6 and 6L6 tubes can be generated.

The guitar input stage (VT1b) is a standard class A triode amplifier. The 1K cathode resistor was chosen to bias this most important amplifier stage into the "sweet spot". The tone controls use the Baxandall tone stack configuration. This circuit has a much more distinct boost and cut operation when compared to many of the traditional Fender circuits. A guitar player friend had the amusing suggestion that the "Bass" and "Treble" labels should be changed to "Balls" and "Grit". The post-tone amplifier stage VT1a is another class A triode amplifier. Again, the 1K bias resistor was chosen for the best sound.

The reverb send amp VT2 gets its input from the tone control recovery amplifier VT1a. The 500K linear pot is used to adjust the reverb send level from half way to full. An audo taper pot was tried here, the linear pot had a better response. Both halves of VT2 are run in parallel, the 560 ohm bias resistor was chosen for the best tube drive level. VT2 runs slightly warm, with a bit of blue glow showing. A standard Fender "Twin Reverb" reverb transformer can be used to drive the reverb, I used a slightly heavier Buddy MC500 transformer.

The reverb return signal goes to two class A triode stages formed by VT3b and VT3a. The reverb return level is set with the 100K audio pot and mixed into the phase splitter stage (VT4) through a 5nF capacitor. The clean (non-reverb) signal is amplified by VT7, a 6AV6 triode wired as a floating cathode-biased stage. The 6AV6 isolates the reverb send and receive signals to prevent feedback, it also forms the heart of the vibrato/tremolo circuit in the Hammonator model 2RVT design.

The balanced phase splitter circuit is formed by VT4a and VT4b. This stage combined with the power tube stage is fairly close to the Fender Vibroverb circuit. The two opposite-phase drive signals are sent to the control grids of the 6V6 power output tubes. An RF power amp trick is used here to reduce potential radio frequency oscillation issues, 10nF capacitors bypass the screen grids to ground. These caps should not be confused with the unpopular tone-deadening control grid caps that were added to Post-CBS Fender Twin Reverb amps.

A triple feedback loop is used between the output transformer and the input of the phase splitter. The low and high cut loops reduce the sub-sonic and ultra-sonic gain, eliminating any tendencies to oscillate and generate radio frequencies. While experimenting with the circuit, some nearly dead power tubes were used, the tubes tended to oscillate when biased to a useful setting. These additions reduced that problem and improved the sound, RF superimposed on audio does not sound good.

A fairly heavy modem isolation transformer from a 300 baud vintage of modem was wired in series to make the low-cut inductor. When the amp is driving a speaker, there can be large resonances in the low bass part of the spectrum. A 12" speaker in an open-backed cabinet had a natural resonance around 70 Hz. Audio at the speaker resonance frequency is amplified to about twice the level as other frequencies, resulting in an exaggerated bass response and distortion. The low-cut feedback circuit offsets this resonance effect.

An earlier version (obsolete) of this amp used a different anti-resonance feedback (ARF) loop that consisted of a 300 ohm resistor, a series-wired modem transformer and a 1.32uF stack of capacitors that was tuned to cancel the speaker resonance. When feeding a purely resistive load, the amplifier has a fairly flat frequency response. The low-cut/high-cut feedback loop eliminates the need to tune the amp for individual speakers.

The 6HU6 eye tube circuit gets its control signal from the output transformer. The signal is rectified, low-passed and sent to the tubes control grid. The 10M bias resistor opens the tubes display farther during quiet operation. The 5K trimmer should be adjusted so that the eye tube display closes completely when the amp is played to maximum power.
Biasing the Power Tubes

If you want more than 18 Watts of power, it is possible to replace the 6V6 tubes with 6L6 tubes, simply re-adjust the bias control. The bias is set by putting a DC volt meter between the Imon1 terminal and ground. The Imon2 terminal can be checked to see if the power tubes are well matched. Both Imon1 and Imon2 should have similar voltages. The 6V6 tubes work well with a bias of around 0.17V (17 mA) and 6L6 tubes work well at around 0.35V (35mA). Tube bias setting is a trade-off between loudness and tube life. Generally, the bias should be set so that the tubes dont become too warm when there is no signal going through them.

Construction:
Here is a photo of the wiring side of the Hammonator 2RVT amp, it is essentially the Hammonator 1 circuit with a few additions.The stock Hammond amp chassis that this project was built on was dirty, rusty and filled with mostly useless parts. A wire brush was used to scrape off the rust and dirt. Leave the original filament wiring from the power transformer to the 6V6 tubes intact. You will need to move one of the filament wires on some of the 6SN7 tube sockets (formerly other tube types). The power transformers high voltage leads can be left connected to the 5U4 socket, the 1N4007 rectifier diodes can be wired to the pins of the 5U4 socket. The output transformers primary wiring should be left as-is.

The ground wires that connect all of the tube sockets should be left intact. Just about everything else can be clipped off, leave all of the transformer wires as long as possible. There were two plug-boards in the center of the amp. All of the wires between the plug-boards and the tube sockets were clipped at the tube sockets and the boards were removed. The wires to the screw terminals were also clipped off. Some of the plug-board capacitors were scavanged for use elsewhere.

A new 3-wire power cord power switch were installed in the small metal wiring box that is located behind the power transformer. Two of the downward-facing holes in the wiring box were expanded to fit the power cords strain relief and the switch. A plastic "pigtail" type of fuse holder was also installed in the box. The power cables green ground wire was connected to the chassis with a solder lug.

The two tall electrolytic capacitors were removed from the chassis. The silver capacitors hole was filed out and drilled to fit the 6HU6 eye tube socket. A sheet metal filler was installed in the black capacitors hole (the photo above was taken before this was done). The volume pedal tower was disassembled and the empty space was used as a "doghouse" for most of the electrolytic capacitors. The caps were secured to the towers bakelite spacers with panduit ties. The tower allows the amp to sit upside down without resting on the tubes, this is very useful when working on the amp.

Build a Receiver Af Noise Limiter For Low-Level Signals Circuit Diagram. A preamplifier in the audio frequency range amplifies a noisy audio signal to drive a diode clipper.Suitable audio input levels would be in the 10-mV to 1-V range. 

This Single cell Charger Circuit Diagram detects a full-charge state and automatically switches to a float condition —from 240 mA to 12 mA. The schema uses the 555 timer.

 Build a Single cell Charger Circuit Diagram

 

This simple key-operated gate locking system allows only those persons who know the preset code to open the gate. The code is to be entered from the keypad within the preset time to operate the motor fitted in the gate. If anyone trying to open the gate presses a wrong key in the keypad, the system is disabled and, at the same time, sounds an alarm to alert you of an unauthorized entry.

Figs 1 and 2 show the block and schema diagrams of the key-operated code locking system, respectively. Connect points A, B, C, D, E, F and ground of the schema to the respective points of the keypad. Keys S7, S16, S14 and S3 are used here for code entry, and the remaining keys are used for disabling the system. It is very important to press the keys in that order to form the code. To start the motor of the gate, press switches S7, S16, S14 and S3 sequentially. If the keys are pressed in a different order from the preset order, the system will lock automatically and the motor will not start.

Fig. 1: Block diagram of simple key-operated gate locking system
.

Initially, 6V is not available at pin 14 of AND gate IC6, so no pulse reaches the base of npn transistor T1 to trigger timer IC5 and, as a result, the gate doesn’t open. To enable the system, first you have to trigger IC4. Pressing switch S7 triggers timer IC4 to provide 6V to IC6 for approximately 17 seconds. Within this time, you have to press switches S16, S14 and S3 sequentially. As a result, the outputs of timers IC1, IC2 and IC3 sequentially go high. These high outputs are further given to gates N1 and N2 of IC6 to trigger IC7 via npn transistor T1. The time durations for the high outputs of IC1, IC2 and IC3 are preset at 13.5, 9.43 and 2.42 seconds, respectively.

When all the four switches (S7, S16, S14 and S3) are pressed sequentially, timer IC7 triggers to start the motor for the preset period to open the gate. Once the time elapses, the motor stops automatically. The ‘on’ time for the motor can be selected by adjusting preset VR5. Here, the minimum ‘on’ time is 5.17 seconds and the maximum ‘on’ time is 517 seconds.

If a switch other than S7, S16, S14 and S3 is pressed, IC5 triggers to energise relay RL1, which disconnects the power supply of the second relay and the system gets locked and piezobuzzer PZ1 sounds an alarm to alert you that somebody is trying to open the gate lock.

Now to stop the sound and reset the system again press any key (other than S7, S16, S14 and S3) from the keypad.

The schema works off 6V DC regulated power supply and can be easily assembled on a general-purpose PCB.

Build a +15V 1 a Regulated Power Supply Circuit Diagram. This is a simple +15-V-1-a-regulated-power-supply schema diagram. The supply receives + 20 Vdc from the rectifier/filter section. This is applied to pins 11 and 12 of the uA723, as well as to the collector of the 2N3055 series-pass transistor. The output voltage is sampled through R1 and R2, providing about 7 V with respect to ground at pin 4. 

The reference terminal at pin 6 is tied directly to pin 5, the non inverting input of the error amplifier. For fine trimming the output voltage, a potentiometer can be installed between R1 and R2. A 100-pF capacitor from pin 13 to pin 4 furnishes gain compensation for the amplifier. Base drive to the 2N3055 pass transistors furnished by pin 10 of the uA 723. Since the desired output of the supply is 1 A. maximum current limit is set to 1.5 A by resistor Rsc whose value is 0.433 0. A 100-J

The schema was designed to build a Regulated Power Supply with Stability at 3A will provide a regulated voltage from 40 V to 70 V in a 3 A current.

There are times when some applications are requiring a regulated power supply that has relatively high output voltage and stability. All of these features are being attained in the design of this schema. The voltage output of the schema can range from 40 V up to 60 V while carrying a current of 3 A while providing stabilization. The construction of the schema is very simple since the components used were available easily in the market. The only thing that matters is how the connection will be ensured.

During the operation, when the schema is delivering 50 V up to 60 V, the transistor Q1 will be hot enough and would require a large heatsink. For voltage output higher than 50 V up to 70 V, the stability of the schema may be found unsatisfactory. This is the reason why the ideal output voltage of the schema is 45 V up to 60 V. In order to alter the output voltage from 40 V up to 70 V, a 470 Ohms potentiometer RV1 is used for the adjustments. However, the potentiometer may also be replaced by two constant resistors with suitable values when the schema adjustment has been done. This is due to the fact that the use of a potentiometer may lead to a 3 V of over voltage.

Regulated Power Supply with Stability at 3A Circuit Diagram

As a reminder, the positive output of the schema should be connected at point A while the 0 V output should be connected at point B. The 0 V reference should not be connected to the ground for the schema to function properly. the use of this 3 A power supply with an average of 50 V schema may be found on various applications that normally requires this rating.

Since this type of schema is easily built, it is being utilized in industrial, educational, clinical, and laboratory facilities. It may come with different additional features such as reduced ripple & noise, overload protection, and short schema & high current protection.

 Build a MT8870 DTMF Telephone Dial Tone Decoder Circuit Diagram. This is a  simple MT8870 DTMF Telephone Dial Tone Decoder Circuit Diagram. In this schema one common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications diagram. The MT8870 isan 18-pin IC. It is used in telephones and a variety of other applications. When a proper output is not obtained in projects using this IC, engineers or technicians need to test this IC separately. 

A quick testing of this IC could save a lot of time in research labs and manufacturing industries of communication instruments. Here’s a small and handy tester schema for the DTMF IC. It can be assembled on a multipurpose PCB with an 18-pin IC base. One can also test the IC on a simple breadboard. For optimum working of telephone equipment, the DTMF receiver must be designed to recognize a valid tone pair greater than 40 ms in duration and to accept successive digit tone-pairs that are greater than 40 ms apart.