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Features:
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.
Construction
CIRCUIT DESCRIPTION
This four tube amplifier is based on the 17W No Frills 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 No Frills Guitar Amp" the third stage and phase splitter is built on a 12AU7/ECC82 dual triode. The output power depends on the supply voltage and power tubes 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.
Fig.1 Guitar Amp Circuit
Fig.2 Full Wave Power Supply with center tapped transformer.
Fig.3 Full Wave Power Supply with diode bridge.
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.
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 | Many | http://www.tubesandmore.com |
| OT1, TR1 | Push-Pull Output & Power Transformers | 1 | Many | 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 | Many | http://www.tubesandmore.com |
| V1, V2, V3, V4 | Power Tubes & Triodes | NA | Many | http://www.tubesandmore.com |
| V1, V2, V3, V4 | Power Tubes & Triodes | NA | Many | http://thetubestore.com |
| NA | Passive Componets, Connectors | NA | Many | 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. |