RCA BA-6A

RCA BA-6A Limiting Amplifier

The RCA BA-6A Limiting Amplifier is built for cost-effective, high-quality performance in FM, AM, and TV sound channels. It automatically controls audio peaks to prevent overmodulation, reducing distortion and interference. This amplifier also maximises transmitter power efficiency by enabling near-max output, boosting average modulation levels by several dB without adding significant harmonic distortion.

RCA BA-6A Limiting Amplifier Details

The RCA BA-6A Limiting Amplifier is designed for efficient, high-quality sound control in FM, AM, and TV broadcast transmitters. It automatically limits audio signal peaks to avoid overloading, thereby minimising distortion and preventing interference with adjacent channels. This function also optimises transmitter power usage, allowing operations close to maximum output levels without significantly raising harmonic distortion.

In recording applications, the RCA BA-6A prevents over-cutting on recording discs during intense audio passages, significantly improving the signal-to-noise ratio. This makes it a valuable tool for both broadcasting and recording studios.

The RCA BA-6A is a three-stage, balanced amplifier that relies on standard, readily available tube types, eliminating the need for special selection or matching. Built with high-quality components, its simple design incorporates only nine tubes, including the rectifier and voltage regulator, ensuring reliability and reducing maintenance costs.

In line with RCA’s high standards for broadcast audio equipment, the RCA BA-6A’s self-contained power supply is mounted on a plug-in chassis, making it easy to install, inspect, and service. All major components, including controls, tubes, and capacitors, are front-accessible.

The front panel features a rotary selector switch with a four-inch meter, enabling monitoring of gain reduction, amplifier tube cathode current, tube balance, and DC filament voltage. The RCA BA-6A also provides plate and heater power to support a pre-amplifier when extra gain is needed. Additionally, the BAL-LIM rotary switch offers filter options with either a single or dual time constant. In the “single” mode, attack time is set to 0.0006 seconds, while in “dual” mode, recovery time extends to two seconds for prolonged peaks.

Features

  • Reduces distortion and prevents adjacent channel interference
  • Cost-effective, delivering high-quality performance
  • Enhances transmitter power efficiency
  • Compact and easy to install, taking up minimal rack space
  • Equipped with a complete rotary switch for metering all key functions

RCA BA-6A

The RCA BA-6A with the front panel removed

Specifications

  • Power Required
    • 100 to 130 volts, 50-60 Hz, 105 watts
    • Transformer taps for 105, 115, and 125 V
  • Impedances
    • Source: 600/150 ohms
    • Input: 600/150 ohms, balanced or unbalanced
    • Load: 600 ohms
  • Input Level
    • Minimum: -24 dBm at limiting verge
    • Maximum: +14 dBm
  • Output Level
    • Maximum (limiting off) at 1000 cps: 38.5 dBm
    • At verge of limiting with output controls at minimum attenuation position: 29.5 dBm ±1 dB
  • Gain: 54 dB ±1 dB at 1000 cps, 600-ohm source to 600-ohm load; input and output controls at minimum attenuation (max. clockwise); signal below verge of limiting.
  • Gain Controls
    • Input: 20 steps, 2 dB per step
    • Output: 20 steps, 1 dB per step
  • Frequency Response (1000 Cycle Reference)
    • Below verge of limiting: ±1 dB, 30–15,000 cps
    • Up to 20 dB gain reduction: ±1 dB to -2 dB (see figure 5), 30–15,000 cps
  • Signal-to-Noise Ratio: 83 dB at verge of limiting. Maximum noise level is -54 dBm with input and output controls at minimum attenuation (max. clockwise), and input and output terminated in 600 ohms resistance.
  • Harmonic Distortion (Total RMS)
    • Below limiting verge: Less than 0.6% from 50 to 15,000 cps, Less than 1.2% at 30 cps
    • At 10 dB gain reduction: Less than 0.75% from 100 to 15,000 cps
    • At 15 dB gain reduction: Less than 1.0% from 100 cps to 15,000 cps
  • Limiting Characteristic
    • Output at verge of limiting: 29.5 dBm ±1 dBm, output control in maximum gain position.
    • Compression ratio above verge of limiting: 20 dB into 2 dB
  • Time Constants
    • Attack
      • Single: 600 microseconds
      • Dual, Fast Action: 600 microseconds
      • Dual, Slow Action: 0.9 seconds
    • Release
      • Single: 0.33 seconds
      • Dual, Fast Action: 0.33 seconds
      • Dual, Slow Action: 2 seconds
  • Signal-to-Thump Ratio
    • 21 dB minimum, 26 dB average, for a series of tests made with different combinations of non-selected tubes in variable gain stage, and an increase in input level of 5 and 10 dB above verge of limiting.
  • Tube Complement: 2 RCA 6SK7, 2 RCA 6J7, 2 RCA 6V6GT, 1 RCA 6H6, 1 RCA 0D3/VR150, 1 RCA 5R4GY
  • Dimensions: 411mm x 356mm x 194mm
  • Weight: 16.8 kg

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The details provided above are drawn from historical documents like advertising brochures or user manuals. They’re shared without bias or review. This info is given solely for your consideration, helping you gauge its usefulness to you.

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