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Coil Audio CA-70 PS6 Amplifier

Single Channel Tube Preamp for Coil Audio PS6 Power Supply Rack, Choose CT-110 or CT-110HN Transformers

  • Coil Audio CA-70 PS6 Amplifier

Price: $1,699.00

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Stock Item: Ships from our shelf quickly in almost all cases when ordered before our ship cutoff times.

Direct Ship: Non-stock item, but normally ships quickly from the manufacturer or alternate warehouse.

Built To Order: Item is custom built per the options chosen and quickly shipped out upon completion.

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Product Description

CA-70 Modular Mic/Line Amplifier

The CA-70 is based on a two-stage circuit invented by Western Electric in 1913. It was licensed and built by various audio manufacturers from the 1930s through the 1950s. RCA, Gates, Western Electric, and Langevin were just a few that utilized this elegant and simple single-ended design.

Each amplifier uses our own custom interchangeable transformers and NOS capacitors, resistors, and octal tubes. With the addition of a flexible pad network, our Negative Feedback tone shaping, and inter-stage volume control, it's like Mid Century with a Modern twist.

Two Different Chassis Versions are Available

The PS-6 version is a fully removable module for use with our 6 channel PS-6 Rack Tray. Each amplifier is easily removable via two thumb screws for flexibility, expandability, and transformer substitution.

The PS-2 version comes factory installed in our PS-2 Rack and PSU. This combines the power supply and modules into a single 3U case creating a compact 2-channel modular solution. The amplifier and power supply are otherwise identical to our larger PS-6 versions.


The (INPUT) Pad section contains a phase reverse switch, and a 5 position attenuation network of Balanced H-pads.

The first four positions are various 150/250 ohm mic pads; -6db, -12db, and -19db. The final (LN) position allows line level signals to run through the amplifier providing tone-shaping capabilities while mixing. It works as both a second-stage booster for other preamps and a summing/buss amp for program and mix material. Two amplifiers can also be chained together to create the multi-stage, high gain recording path of a vintage tube console.

The NF, High, and LOW controls all interact to create a unique tone-shaping circuit.

The NF control varies the amount of Negative Feedback present in the circuit. Counter-clockwise brightens and moves the sound forward while raising harmonics and sensitivity. Turning it clockwise increases negative feedback, producing a darker tone with a smooth, dampened harmonic structure.

The HIGH switch transitions from the natural openness of the tubes to a gentle filtering of upper frequencies. The LOW switch reacts with the NF, boosting or cutting low frequency while moving the low end from front to back in the sound stage.

The OUTPUT control knob is placed between the 1st stage 6J7 and 2nd stage 6C5 tubes.

It sets the final level and offers further control of the two-stage gain structure.

CA-70 Amplifier Features

  • Two-stage 6J7/6C5 vacuum tube circuit
  • 42db-54db of available gain
  • Flexible input pad section for mic or line level operation
  • Transformer balanced. 150 Ohm or 10k input, 600 Ohm output
  • Interchangeable/Optional input and output transformers
  • NOS tubes, signal caps & resistors, PEC 2W carbon pots
  • Up to Six CA Series Amplifiers mount into our PS6 Rack
  • Up to Two Amplifiers in our PS2 Rack
  • Hand Built and Tested in the USA

CT-110 Transformer Features

  • Nickel / Iron mic input style
  • Punchy, 1960's small signal coil design
  • Excels at all around use, high transient material
  • Forward and rich midrange, smooth saturation of highs and lows

CT-110HN Transformers Features

  • Super-Mu mic input style
  • Hi-fi, 1950's style coil design
  • Excels at detailed delivery, extended top and bottom
  • Smooth and breathy saturation

Warranty Information

Our ONE WITH EVERYTHING ZEN WARRANTY extends the standard manufacturer warranty by one year, see our ZEN WARRANTY page for details.

Customer Reviews / Q&A Discussion