BA-60 OTL AMPLIFIER
A 1960s OTL amplifier, completely rebuilt and re-biased for a quieter, wider, more refined sound.
It started as a scrapyard find.
A 1960s BA 60, its front panel gone and every transistor burnt out. An output-transformerless (OTL) amplifier from the brief moment the industry was crossing from tubes to transistors, using a single capacitor where the output transformer would normally sit. Warm, thick, and soft — and, by modern standards, distorted (THD < 0.3%).
If every failed and obsolete part were replaced with the best modern equivalent, how far could the sound be pushed? This is the answer. Rebuilt, re-panelled, and re-biased until its own maker wouldn't recognise it: quieter, wider, far more detailed — an old shell brought fully back to life, where the vintage character and HiFi performance live in the same box.
What changed.
Rectification — SiC Schottky, for a cleaner supply
Coupling capacitor — Miflex KPCU
Power-supply bypass — Duelund JDM
Input resistor — TX2575 foil
Output transistors — modern MJ15003, isolated on aerospace ceramic
Bias / DC offset — 25-turn precision trimmers; midpoint holds a true 0 V, no drift
Thermal compensation — an NPN transistor rewired as a diode, mounted against the output devices
Bias current — raised from the factory's 14 mA to 100 mA, into near class-A, stable at 42 °C
Front panel — new stainless steel, with a collected vintage meter and switch.
An old shell. A new sound.
