Lighthouse Electric Vacuum Tube Project

Build this Guitar Amplifier with Tone Controls
CIRCUIT DESCRIPTION
This four tube amplifier is based on the "17W Budget Guitar Amp". Two additional gain stages are built on a 12AT7/ECC81 dual triode. First stage V1a drives the passive tone controls network. Due to signal loss in the tone control circuit, V1b is a second gain stage. The signal is taken from the "Main" volume control potentiometer to the third stage and finally to the phase splitter. Unlike the "17W Budget Guitar Amp" the third gain stage and the phase splitter are built on a 12AU7/ECC82 dual triode. The output power depends on the supply voltage and power tubes types used. A push-pull amplifier produces less distortion than a single-ended one and produces more power than two single ende amps with same output tubes.

Two power supply topologies are shown below. Separate transformers for plate and filament supply are common. Some exaples are shown below. The voltage and current specification depends again on your power tube requirements. Push-pull operation has also the benefit of hum cancellation. Any A-C hum voltage from the power supply will produce currents in opposite directions in the OT primary winding, effectively canceling out each other. However, this advantage applies only to the output stage. Hum introduced in preceeding stages must be filtered out with capacitor-resistor filters or chokes. Center tapped filament circuit uses anti-phase wiring for the gain stages where the center tap of the secondary wiring is grounded. The benefit of this method is reduced 60Hz hum.

12-50W Guitar Amp
Fig.1 Guitar Amp Circuit

Full Wave Power Supply
Fig.2 Full Wave Power Supply with center tapped transformer.

Full Wave Power Supply
Fig.3 Full Wave Power Supply with diode bridge.

Full Wave Power Supply
Fig.4 Center-Tap Filament Supply.


WARNING Potentially lethal voltages can be present. Do not touch any part of the device with bare hands while under power. After disconnecting power, wait until filter capacitors are discharged. Measure voltage with voltmeter to be sure. If you do not know how to handle high voltage circuits, do not build this device. Get help from a qualified technician.

Construction
Contstruction is similar to the 17W No Frills Guitar Amp. Use that maual for guidance.

AMPLIFIER PARTS SUPPLIERS
REF. # DESCRIPTION QUANTITY PART No: SUPPLIER
NA Steel chassis Hammond 1 generic http://www.tubesandmore.com
OT1, TR1 Push-Pull Output & Power Transformers 1 generic http://www.musicalpowersupplies.com
OT1 Output Transformer 6L6 25W P-P 1 P-TF41318 http://www.tubesandmore.com
NA Tube sockets, Phono Jacks, Hardware NA generic http://www.tubesandmore.com
V1, V2, V3, V4 Power Tubes & Triodes NA generic http://www.tubesandmore.com
V1, V2, V3, V4 Power Tubes & Triodes NA generic http://thetubestore.com
NA Passive Componets, Connectors NA generic www.mouser.com, www.jameco.com


DISCLAIMER OF LIABILITY:
THESE PROJECTS ARE PROVIDED 'AS-IS', WITH NO WARRANTY OF ANY KIND.
USE OF THESE CIRCUITS SHALL BE ENTIRELY AT THE USER'S OWN RISK.
The publisher of this web site does NOT assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

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