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Coil Audio CA-70S

Mono Tube Preamp and Line Amplifier, Custom Transformer In and Out

  • Coil Audio CA-70S Front
  • Coil Audio CA-70S Angle Right
  • Coil Audio CA-70S Angle Left
  • Coil Audio CA-70S Rear

Price: $1,699.00

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Direct Ship, Non-Stock But Normally Ships Quickly

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.

Visit our Shipping Page for cutoff times for FREE (USA), USPS or FedEx.

Product Description

The CA-70S 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. With the addition of a flexible input pad network, our Negative Feedback tone shaping, and inter-stage volume control, it's like Mid Century with a Modern twist.

Each amplifier utilizes our CT110HN and CT41 custom transformers, as well as the same high end and vintage components as our larger PS6 modules.

CA-70 Amplifier Features

  • 2U steel enclosure with integrated power supply
  • CT-110HN high Nickel input, and CT-41 output transformers installed
  • Two-stage 6J7/6C5 vacuum tube singe ended circuit
  • 42db-54db of available gain
  • Flexible input pad section for mic or line level operation
  • Transformer balanced. 150 Ohm mic input, 20k Bridging line input, 600 Ohm output
  • NOS tubes, signal caps & resistors, PEC 2W carbon pots
  • Linear regulated Power Supply with slow B+ ramping to prolong tube life
  • Hand Built and Tested in the USA


The (INPUT) Pad section contains a Mic/Line selector, phase reverse switch, and a 4 position attenuation network of Balanced H-pads.

The LINE/MIC switch toggles between LINE or MICROPHONE level inputs. Select “MIC” for standard low level microphone signals. Select “LINE” for any balanced line level signal such as the output from a tape machine, DAW, mixer, keyboard, drum machine, or other pre amps. “LINE” mode allows it to work as a tone shaper/booster for other outboard gear, a second-stage booster for other preamps, or a summing/buss amp for program or mix material. It also enables easy chaining of multiple amplifiers to create the multi-stage, high gain signal path of a vintage tube console.

The Rotary Selector switches between 0, -6, -12, and -19dB input pads. This allows the input to handle high output microphones or loud signal sources. These pads are in the path whether you are in “LINE “ or “MIC” mode.

The NF and LOW controls 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 LOW switch reacts with the NF, boosting or cutting low frequency while moving the low end from front to back in the sound stage. Most effective when the NF knob is between 11:00 and 5:00, The more Negative Feedback, the more reactive.

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.

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