KT-88 Push-Pull Project with Hashimoto Transformers
This
amplifier was featured on the February 2004 Issue of the "High-Fidelity Audio:
Radio Technology" by Mr. Tadaatsu Atarashi. Mr. Atarashi originally
built this amplifier as the fixed bias EL34 Class B
Push-Pull monaural amplifier featured on the January 2003 Issue
of the "High-Fidelity Audio: Radio Technology". Then, Mr. Atarashi modified the amplifier to fit for KT-88 AB1 Push-Pull Ultra-Linear
operation.
As you could notice by comparing these two amplifiers, there were very minor
changes between them except the differences in power
supply circuit. Instead of the original full-wave bridge rectifier for the
B+ power supply, Mr. Atarashi chose the half-wave rectifier for both B+ and bias
power supply on this amplifier. According to Mr. Aarashi, the half-wave rectifiers increase
the depth of sound image by eliminating the soft bass sound (need testing to
verify his opinion). For this purpose, Mr. Atarashi used a 30A
high-voltage-rated Schottky Barrier Diode. Mr. Atarshi also connected the
anode of this diode to the ground. By doing this, Mr. Atarashi claims it
improves the sound (need testing also).
Because Mr. Atarashi was modifying two mono-bock EL34 power amplifiers
to the KT-88 version, he
compared the sound of amplifiers after just one amplifier was converted to
the half-wave rectifiers (another was with a bridge rectifier for the B+ and a
full-wave for the bias). According to this comparison, Mr. Atarashi
concluded that the amplifier with the bridge and full-wave rectifiers sounded brighter,
also yielded too much bass sound. On the other hand, the amplifier with the half-wave
rectifiers sounded more responsive and realistic. Evidently, Mr. Atarashi
preferred the sound from the half-wave rectifiers over the sound from the
full-wave and bridge rectifiers.
