Wiring & diagram Info

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 schema. Builders can start with the Model 1 schema and easily add the Model 2RVT Vibrato/Tremolo schemary 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 schema 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 schema 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 schemary was modified from the original Hammond schema. 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 schemary. 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 schema has a much more distinct boost and cut operation when compared to many of the traditional Fender diagram. 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 schema in the Hammonator model 2RVT design.

The balanced phase splitter schema is formed by VT4a and VT4b. This stage combined with the power tube stage is fairly close to the Fender Vibroverb schema. 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 Lcd 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 schema, 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 schema 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 schema 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 schema 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.

This simple but complete Theremin with Inverter Gates is constructed using only two inverter chip plus one regulator IC. This Theremin schema consist of five functional blocks: power supply regulator, hand controlled oscillator, null oscillator, mixer, and filter. Here is the complete schematic diagram.

The power supply regulator consist of LP2950 regulator IC, which stabilize the voltage from battery to 5V. You can use more popular 7805 IC for this, but since the power consumption of this Theremin schema is very small, then you can use 78L05 which is smaller.  CR1 diode is used to protect from inappropriate battery polarity,  shorting the battery voltage together with R8 100 Ohm resistor which prevent the large current when the battery is installed in wrong direction. Although the inverter chip will work well for 9V battery, there is a benefit of using voltage regulation to regulate the battery voltage at lower voltage level, that the voltage will remain constant for until the end of battery life. This will avoid frequency drift of the Theremin’s null oscillator  which should be carefully adjusted to zero the output frequency, which can be affected by the supply  voltage.

The hand proximity sensor is an oscillator which has antenna extension which shift the capacity coupling in the loop. This capacitance shift occur when we move our hand approaching the antenna. Since this change is very small in percentage, we need this oscillator to be high enough to produce notable frequency difference.  This oscillator block is built around U1A, U1B, and U1C. This oscillator give oscillation at around 73kHz. This frequency is not directly audible, we have to process this signal further to produce audible signal.

Null oscillator is employed to produce a constant frequency oscillation that will be used to produce differential frequency which is audible.  This oscillator block is built around U2A, U2B, and U2C. This null oscillator should be adjustable to set the null point where the Theremin should produce no oscillation at certain hand position.  At this point, the null oscillator should be adjusted to have  same frequency with the hand controlled oscillator since the audible Theremin output is the product of the difference between hand controlled and null oscillator frequencies.

The mixer is used to mix the signal from two oscillators, the hand controlled and the null oscillators. This mixer produce an output which contain many frequency components, not only the difference but also the original and the sum, since the amplifier U1F is basically a digital inverter which has non-linear transfer function. Fortunately, all the frequency components, except the difference, will be much higher than the needed signal and inaudible. This make it easy to remove by simple low pass filter to obtain only the differential frequency component.

As stated before, we need to obtain only the audible frequency component by low-pass filtering. Although the high frequencies is inaudible, we still have to remove it since it can cause damage in audio power amplifier is the level is too high. It can distort the audible signal, and it can eat the electric power like ghost, frying your amplifier or at least make it overheated. This  Theremin schema use simple low pass filter consist of C4, R5, and R7 for the passive stage, and C2 inside the inverter amp loop.

This is a simple PIC Security System Dials Your Cell Phone Circuit Diagram. Do-it-yourself phone dialer security system calls your cell phone, office etc. whenever a door or window is opened, or panic button is pressed. Great Home Alarm.

PIC Security System Dials Your Cell Phone Circuit Diagram



The schema consists of a small PIC microcontroller, assembly program, and a few other parts to detect a switch closure from an open door, window, or manual push button and then dial the cell phone number, and transmit a steady tone to indicate the source of the call. The schema uses the pulse dialing system to interrupt the line connection a number of times to indicate each digit. Pulse dialing (the oldest form of dialing) works by actually disconnecting or "hanging up" the phone line a number of times to indicate each digit. For example, the digit "5" would be dialed by disconnecting and reconnecting the line 5 times in short intervals of about 100mS. There is about a 1 second pause (with the line connected) between each digit. The timing is not critical and I was able to dial 411 and connect to the local information service just using a momentary push button switch in series with the phone line.

Circuit Operation:
In operation, the switch closure is detected on pin 7 of the processor which activates the reed relay and takes the line off-hook for 3 seconds to establish the dial tone. The processor then dials the number by opening and closing the relay a number of times for each digit. When dialing is complete, the processor waits 3 seconds and then transmits a steady tone of about 300Hz for 30 seconds through the modem transformer. The call is then terminated and the processor waits for the switch to open before resetting.

Design Considerations:

The PIC16F628 (18 pin) processor was selected because I had a few on hand and my homemade hardware programmer only accepts 18 pin devices. A smaller 8 pin device could have been used since only three I/O lines are needed, but the difference in cost is only about $1.50. One of the I/O lines (RA5) is used for programming and is always an input, but can used as a functional input so the switch closure could be detected on this line thus eliminating the need for one pullup resistor. But I elected to use 3 consecutive I/O pins (7,8,9) of the 8 bit port B and leave RA5 pulled up with a extra 10K resistor.

The output pins (8,9) that drive the relay and transformer are limited to 25mA of current each, so an extra transistor (2N2222A) was needed to supply additional current to the relay coil. The transformer resistance is around 100 ohms, so an additional 330 ohm resistor was added in series with pin 9 to limit the transformer current to around 10mA. An LED indicator and 330 ohm resistor were used on pin 8 to observe the dialing activity and indicate the line status. Several of the parts (relay, transformer and blocking capacitor) were obtained from an old 56K modem card.

The schematic shows a 47uF / 50 volt non-polarized capacitor used to block DC current to the transformer, however a regular polarized 50uF cap could be used if correct phone line polarity is observed. The modem was probably designed to work with unknown polarities at different locations, so a non-polarized cap was used. Its possible the cap and 470 ohm resistor can be replaced with a single resistor in series with the line to set the "off hook" line current to around 20mA. This may cause partial saturation of the transformer and reduced audio level, but might work well enough.

The power supply voltage is not critical and a 4.5 volt supply from three AA batteries should work. Or a switching type regulated 5 volt wall transformer can be used. The problem is insuring the relay gets enough voltage to operate. The rest of the schema should run on reduced voltage. I used a 4.2 volt cell phone charger that worked well.

     In the operation is still a lot of these "dinosaurs" of the mid 90s. A characteristic feature of built-in amplifiers such devices - they are designed for load 2 ohms and have a good supply of power. This is due to the fact that in the middle position fader front and surround speakers are connected in parallel. However, to use them in conjunction with acoustic component is impossible. The reason is simple - the introduction of the fader increases the output impedance of the amplifier, which leads to a change in crossover. Therefore, the only option enhancers such devices with modern acoustics - dual channel configuration, with the fader excluded from work.

     In this version, you can add a subwoofer to include it in a "mixed-mono". Since the relationship between the levels regulate front speaker and subwoofer impossible, depending on the sensitivity applied to select one of the heads of connectivity options.

     Option A is used in the case where the sensitivity of the front speakers 3-5 dB higher than that of the subwoofer. In this embodiment, they are connected to the amplifiers are not bridged, and the usual way, and the power supplied to them is not more than 7 w / 4 ohms. To obtain sufficient volume of the front acoustic desirable to use high-sensitivity head about 91-93 dB. Pay attention to their phasing - one of the "poluusiliteley" inverting the second - non-inverting. HPF cut formed by the capacitors C1 and C2 can be chosen arbitrarily, but the presence of capacitors is crucial - they do not miss out on the dynamics of the DC component from the output amplifiers. Front head shown conventionally broadband, but they may be coaxial or component.

     Option B is used in nearly all heads of sensitivity. The presence of capacitors C1, C2 for the normal functioning is not necessarily because it is used in a bridge connection. In the absence of capacitors in the passband head subwoofer filter work in parallel. This reduces the load impedance to 2 ohms, but the amplifier is designed. Subwoofer in both cases the second-order filter (C3L1R1).

The UCC27518 and UCC27519 single-channel, high-speed, low-side gate driver device is capable of effectively driving MOSFET and IGBT power switches. Using a design that inherently minimizes shoot-through current, UCC27518 and UCC27519 are capable of sourcing and sinking high, peak-current pulses into capacitive loads offering rail-to-rail drive capability and extremely small propagation delay typically 17 ns.

The UCC27518 and UCC27519 provide 4-A source, 4-A sink (symmetrical drive) peak-drive current capability at VDD = 12 V. The UCC27518 and UCC27519 are designed to operate over a wide VDD range of 4.5 V to 18 V and wide temperature range of -40°C to 140°C. Internal Under Voltage Lockout (UVLO) schemary on VDD pin holds output low outside VDD operating range.