KT88 SINGLE ENDED (SE) TUBE AMP

July 11, 2008 | Leave a Comment

KT88 AMPLIFIER

This diy audio project is a single ended (SE) KT88 tube amplifier. The design has been based largely around Mikael Abdellah's KT88 SE Tube Amplifier design from 2003. A schematic of the single ended KT88 amp that I have built is shown below in Figure 01.

Figure 01: KT88 Tube Amplifier Schematic

The amplifier section is generally the same as Mikael's, but I have added a switch that will allow me to switch between triode or ultralinear operation (the original circuit is only ultra-linear). Also, the power supply to the 6N1P preamplifier section has been beefed up with the addition of a choke.

POWER SUPPLY

The power supply is based around a 5U4-GB dual tube rectifier and is shown in Figure 02 below. My friend Arnold Cruz helped me modify the PSU circuit from the original done by Mikael.

Figure 02: 5U4-GB Tube Power Supply Schematic

CONSTRUCTION

Photograph 01: Dry Fit - KT88 Tube Amplifier

Photograph 02: Enclosure Construction - KT88 Tube Amp

Photograph 03: Finished KT88 Single Ended (SE) Tube Amplifier

Parts required for the KT88 Tube Amplifier project are available from TubeDepot.

REMARKS

After I finished wiring the SE KT88 amp, I fired it up, and what a glorious sound! It has better sound than my Push Pull KT88 commercial amp. Maybe due to the SE operation.

You can swap the KT88 tubes with EL84 and the 6N1P with a 6DJ8/ECC88/E88CC. I have tried Siemens EL34, JJ EL34, and Electro Harmonix EL34 tubes. A friend lent me a pair of GEC KT88, and the amp sounded great. The KT88 tubes sound better, but they are quite expensive, the EH EL34 is 1/3 of the price, but it sounds good too! My favorite selction of tubes for this amp are an Amperex Bugle Boy 6DJ8 (in place of the 6N1P) and Siemens EL34 on triode mode.