|Harman Kardon Citation II stereo power amplifier (1959-1962)|
The new breed of inefficient speakers such as the AR-3's and KLH Model Nine Electrostats required a lot more power than before, and many American manufacturers such as Marantz, McIntosh and Scott were beginning to develop high-output stereo amplifiers.
Designed from a professional sound engineers perspective by Stewart Hegeman, the Citation II featured a very high output (60 watts per channel), low distortion and an extremely high bandwidth (at 20W: 18 Hz to 60,000 Hz +0, /– 1.0 dB ). Weighing 70 pounds (almost 32 kg), this power amplifier looked good enough to eat with its chocolate coloured transformers and golden chassis.
The circuit consisted of a pentode input stage, followed by a pair 12BY7 video pentodes as a differential phase splitter (the video pentode supplied a bandwidth of well over a megahertz in the input stage). The output stage utilised a pair of KT88's for each channel, each valve having its own bias control as well as an AC balance control. A small meter at the rear of the chassis was provided for measuring bias and AC balance. Three feedback loops were incorporated, giving 32 db of overall feedback with unconditional stability.
The output transformers were superb, built by the Freed company in New York. Huge, well-potted units, they boasted extremely wide response characteristics with leakage inductance kept to an absolute minimum. Only the highest grade core materials available were used, which, lowered the effect of core distortion to a region well below the limit of human hearing. With feedback, the Citation II transformers were capable of high frequency response up to 270,000 cycles!
The power supply consisted of four silicon diode rectifiers, filter choke, heavy duty electrolytic capacitors and a large, potted power transformer (also made by Freed).
Highly sought after today, a mint condition Citation
II can fetch upwards of $US 1800 with complete but average condition units
selling for between $700 and $1200. A perfect match for the Citation
I preamplifier [link].