Kaivalya – Tube Mono Power Amplifier

For more power than is easily available from 2A3 and 300B direct-heated triodes, we offer the EL84-based Kaivalya mono amplifiers. This project began as a custom commission for an audio magazine editor. It is now a production item in our top White Range. The brief submitted for this project asked for 45-type refinement and speed, lower THD, higher linearity, more bandwidth and 25 watts of power.

Our solution was a class A push/pull pentode power section with four EL84/6P14P-EV and solid-state rectification. This stage is driven from a single-ended 12AU7/ECC82 driver. Interstage coupling by our own 11-section transformer with 38 windings eliminates coupling capacitors. Between driver and power stage, we apply a very minimal 0.3dB of local negative feedback for a significant reduction in harmonic distortion.

The minimalist signal path of five tubes and two transformers is accompanied by a very overbuilt power supply. It includes three 10H Trafomatic smoothing inductors for the G2, driver stage and high-voltage power supplies.

There are custom Trafomatic standby, power and dual C-core output transformers, current-limiting overload transistors and a LM317T voltage stabilizer for the driver heater supply. The mono amplifiers are finished in high-gloss white lacquer for the copper-lined solid wood casing and four transformer covers.

The screwless top plate with engraved tube markers, the terminal plate and the power knob are fine aluminum. Custom paint colors are available by request. An engraved plexiglass tube shield is lit from below with concealed white LEDs during operation and orange in standby. WBT speaker terminals offer 4- and 8-ohm connection. The input sensitivity is 3V to optimize volume range of a partnered preamplifier.

Kaivalya – Image gallery


Output power: 25 Watt
Class of operation: Push-Pull (class A)
Tubes complement: 4x EL84 (6P14P-EV), 1x ECC82 per mono
Outputs 4 – 8 Ohms
Input sensitivity: 2.8V rms
THD %: 0.03% – 1W/1KHz, 1% – 25W/1KHz
Frequency bandwidth: 10Hz(-1dB)-95KHz( -3dB)
S/N Ratio: 82 dB
Input inpedance: 100K
Size: 430x290x165 mm
Weight: 20 Kg