Усилители мощности моно — Coincident Frankenstein MkV

The Frankenstein MkV is a single-ended 300B valve monoblock from Coincident Speaker Technology of Maple, Ontario, Canada, designed by Israel Blume, who studied existing 300B circuits and other directly heated triodes such as the 2A3 and 45 before creating it. The full name is Frankenstein M300B MkV, and it costs USD 7,799 per pair, delivered in the US and Canada. It follows the MkIV, which used a 6EM7 driver valve, and Coincident also makes a stereo version of the Frankenstein 300B. The 300B is a directly heated triode, in which the filament itself acts as the cathode, and it was first made for telephone line amplifiers before it became a common audio output valve.

Key specs that matter

Each monoblock runs in pure Class A and delivers 8 W RMS, optimised for loads of 8 to 16 ohm. The valves are a 6SL7 input and driver, a 300B output triode and a 5U4GB rectifier. Frequency response is 10 Hz to 20 kHz within 1 dB, THD is below 1% from 20 Hz to 20 kHz, input sensitivity is 700 mV and input impedance is 100 kOhm. Signal to noise ratio exceeds 90 dB. Each amplifier measures about 381 mm wide, 305 mm deep and 216 mm high and weighs 17.5 kg.

Engineering and use context

A single-ended stage uses one output valve per channel, with no push-pull pair, so the 300B works on the whole waveform in Class A. The driver couples to the 300B through a 6N copper interstage transformer instead of a coupling capacitor, and the output and power transformers are also wound with 6N copper. The power supply uses only polypropylene capacitors, with no electrolytics, and stores 140 joules of energy. An auto-bias circuit sets and holds the operating point of the 300B, so it does not need manual adjustment as the valve ages. As a valve rectifier, the 5U4GB lets the high-tension supply rise slowly after power is applied, sparing the 300B a sudden voltage. Wiring is point to point by hand, using Coincident's Quantum Leap wire. The chassis is triangular and made of mirror-polished stainless steel. Mains voltage can be set to 115 or 230 V on the rear panel. With one chassis per channel, each side gets its own supply and transformers, so the channels do not share any part of the supply.

Pairing

With its low output, the Frankenstein needs high-sensitivity speakers of matching impedance, such as Coincident's own designs or horns, in a room of about 20 m2. Its input sensitivity suits valve and passive preamplifiers.

Alternatives

The Coincident 211PP Dragon MkII is the push-pull 211 monoblock rated at 75 W continuous.