The Fisher 50-C

 The Fisher Master Audio Control, Model 50-C has been designed to specifications so far beyond those of the ordinary unit of this type, that they will long serve as the ultimate standard of comparsion. In flexibility, flawless performance, beauty of appearance and workmanship, the 50-C is a masterpiece. In sctual use, its performance will be limited on;y by the quality of the associated equipment.

 The Fisher Model 50-C features high gain with extreme reserve output voltage. Intermodulation distortion is so low as to be virtually unmeasurable. The self-contained power supply, completely shielded with DC for all filaments, results in a hum level that is inaudible even under extreme operating conditions. The circuit is all-triode, with fully shock-mounted tubes. Cathode-follower input and two cathode-follower output stages assure isolation of all control circuits, plus independence from load conditions, lead lengths, etc. The Model 50-C can be used with any amplifier.

 

Specifications:

Phonograph Preamplifier:  Has two cascaded triode stages.

Inputs (Total of five):

3 x high-level inputs (0,5 megohm)

1 x low-level magnetic phono input to match all makes of cartridges.

1 x microphone input (2,2 megohms)

Output Impedances (Both recorder and main audio outputs are from cathode followers, permiting lead lengths up to 200 feet. Recommended load  impedance):  100,000 ohms or greater, 7500 mmf or less.

Maximum Gain: 

From high level input:  22,5 dB

From low level input:  50 dB

Harmonic Distortion: 

0,02% at 1 volt,

 0,05% at 5 volts

0,15% at 10 volts

0,4% at 15 volts

Intermodulation Distortion:

0,08% at 1 volt

0,2% at 5 volts

0,5% at 10 volts

1,6% at 15 volts

Frequency Response:  20 Hz - 20,000 Hz  ±1 dB, (with controls in uniform response position)

Hum and Noise level: 

On radio input - better than 100 dB below normal signal (2 volts output) with volume control at zero.

Better tnan 90 dB below normal signal with volume control at maximum.

On phono input -66 dB below output with a 10 mV input signal.

Controls (Total of eight):

Volume Control; operates either conventionally or as a Loudnes Control accurately calibrated to the reciprocal of the Fletcher-Munsen curves

Loudness Control Switch; eliminates loudness compensation when desired

Selctor Switch; has five position (see Inputs above)

Low and High Frequency Equalization Switches; provide independent adjustment of low frequency turnover and high frequency roll-off (16 combinations)

Bass and Treble Tone Controls; produce up to 16 dB of boost or attenuation at 50 and 10,000 cycles respectively. Can be set for uniform response

Power Switch; operates self-contained power supply and three spare AC receptacles.

Five Independent Level Controls; equlize various input signal levels and permit optimum loudness control setting.

Power Supply:  Self-contained and completely shielded, including a full-wave selenium rectifier for B-plus and bridge-type selenium for Dc filaments

Power Source:  105 -125 Volts, 50 - 60 cycles

Tube Complement:  2 x 12 AX7; 1 x 12 AU7

Chassis:  is of etched aluminum

Dimensions (W x H x D):  14¾ x 3½  x 6⅛ inches