Plessis Setup & Info

Plessis Model A - Basic Setup - by Charl du Plessis

See also Understanding Valve Amplifiers

Plug the source, speakers, and all of the necessary cables into the Model A amplifier. Unplug the eight tubes and reseat all of them to ensure positive contact. This will eliminate static and other problems.

Here is the basic checking and warming-up procedure for this integrated amplifier.

1. Push the power switch on the front panel to turn the integrated amplifier on. The light on the power switch will flash while the tubes are being heated to operating temperature. At this time the electronic circuits are checked for possible problems. Should a problem be detected the amplifier circuit will not switch through to the power on position.

2. The electronic checking procedure should take around 40 seconds to complete. With the amplifier circuit working as expected the display light on the power switch will stop flashing and the controls will become active enabling you to change source, volume, and check the bias.

3. My recommendation at this stage would be to check the bias of the four power tubes. Depressing the dipswitches located in front of each tube, by pulling/pushing the dipswitch towards the front of the amp and checking the measurement on the "m/a" meter do this. Use a small flat screwdriver to turn the potentiometer of each tube in the desired direction or until you have the desired measurement of around 42 "rn/a" for all four of the tubes. Maintaining the bias setting is quite important as this will give you great sound and maximise the lifespan of the power tubes.

4. The amplifier takes some time from start to settle in. Run the amplifier for 20 to 30 minute's and recheck the bias settings. Re-check in a few hours for accuracy. You will find the bias setting might vary from time to time as a result of the fluctuations in the power supply and/or changes in tube conditions.

5. When you change source inputs we recommend turning the volume level down to zero.

6. In regards to the UL and TR settings at the back of the amp. (UL) Ultra linear selection provides a higher output in power/volume. (TR) Triode mode will provide lower power output but should improve the sound quality. Try both settings and discover what works better in your system.

7.The speaker terminals indicate 8 ohm, 4 ohm and negative on both sides. Use the appropriate impedance selection tap for your specific speaker pair.