The Radial Space Heater is an 8-channel tube overdrive from Radial that can be used as an analog summing mixer or as a multi-channel studio effects device1. Each channel runs a 12AX7 vacuum tube gain stage, and Radial describes the result as "a range of effects from subtle warmth and grit to full harmonic distortion"1. It is a rack unit aimed at recording and live sound rather than a pedalboard piece, and it is discontinued: Radial states that "this product has been discontinued and is no longer shipping"1.
Both the rack Space Heater and the single-wide Space Heater 500 module are discontinued and no longer shipping14. Radial still publishes the specifications and a user guide for owners1.
What it is and what it does
The Space Heater is an analog summing mixer and studio grade 12AX7 tube overdrive in one box2. The audio circuit is a Class-A tube gain stage with IC buffers2. Eight channels each pass through their own tube, and the unit can run clean or run dirty2. Radial positions it for three jobs: as an analog summing mixer that adds tube character to a mix, as a multi-channel studio effects device, and as an 8-channel effects insert using its individual outputs1.
A related product, the Space Heater 500, is a 500 series module version of the eight channel Space Heater56. Guitar Interactive Magazine reported it shipping in July 2015, quoting Radial on the original's reception: "When we launched the eight channel Space Heater, it became immediately apparent that we had no choice but to make a module"6. The 500 version is designed to work following API's original specifications and is compatible with API and other 500 series racks7.
The controls: Heat, Drive and Level
The three main controls work together, and Radial notes that the Heat setting, the Drive position and the Level position all affect the published specifications2.
| Control | What it does |
|---|---|
| Heat | Sets the B+ plate voltage going to the 12AX7 tube: 35, 70 or 140 volts, for more or less distortion3 |
| Drive | Controls the input level of the tube circuit5 |
| Level | Sets the output from the tube drive; Radial says it "acts like a master volume on a tube guitar amp"5 |
| On | Turns on or bypasses each of the four channel sets3 |
The Heat switch is the heart of the unit. Lower plate voltage starves the tube and produces more distortion; at the highest setting of 140 volts, the tube sees its optimal power and produces a clean, warm sounding signal with plenty of even harmonic overtones7. Radial says the 3-position HEAT switch "greatly changes the type of distortion that the tubes will produce"7. Adjustable LEVEL and DRIVE tailor the level of distortion from subtle to extreme1.
Specifications by Heat setting
Because the plate voltage changes how the tube behaves, gain and noise both shift with the Heat setting2.
| Heat setting | Gain | Noise floor at max gain |
|---|---|---|
| 140V | +33dB | -64dBu |
| 70V | +29dB | -66dBu |
| 35V | +27dB | -70dBu |
Other measured specifications from Radial's spec sheet2:
- Frequency response: 20Hz to 20KHz, +0/-3dB
- Dynamic range: 96dB
- Maximum input: +22dBu
- Clip level: +26dBu
- Input impedance: 50kΩ in parallel with the load device when bypassed, 100kΩ active
- Output impedance: 180Ω balanced output, 100Ω mix bus
- Common mode rejection ratio: -70dBu at 55Hz
- Equivalent input noise: 103dBu
The chassis is a 14 gauge steel chassis and outer shell, and the unit is rated for use in dry locations only between 5°C and 40°C2. Warranty was the Radial 3-year transferable coverage2.
Power and connections
Power comes from an external switching supply taking 100V to 240V AC, with a 1600mA output delivered through a 5-pin XLR2. The product page describes this as a 5-pin locking XLR connection for the external power supply3. Inputs are 1/4" TRS and D-Sub2. The Space Heater 500 module uses XLR input connectors instead, and adds HPF, LPF, OmniPort and EQ controls8. On the 500, the OmniPort provides an unbalanced instrument input when the module is used with the Radial Workhorse rack58, and its In switch bypasses the circuit to compare wet and dry signals5.
Uses on drums and in-ear monitors
Radial's product page suggests two applications beyond summing. For drums, it says to "set the Space Heater to 25 volts to create humungous tube crunch and adjust the drive and level to suit," using individual sends as outputs or mixing down to stereo through the built-in bus1. For in-ear monitors, the unit adds the natural compression of tube distortion into the signal path, which Radial describes as a way to "get the natural feel and tone back into your in-ear monitors"1. On the 500 module, Radial suggests placing it in line with a mic preamp to record its harmonic distortion while tracking4.
Not the Sushi Box FX Space Heater
Players searching for "Space Heater" may also find a pedal of the same name from Sushi Box FX, a different maker. That product is a simple 12AX7 preamp pedal with Gain and Level controls, center-negative power like most guitar pedals, designed for tube warmth with a little breakup in a compact package9. It shares nothing with the Radial unit beyond the name and the tube type.
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Questions
Is the Radial Space Heater discontinued?
Yes. Radial states that both the rack-mount Space Heater and the Space Heater 500 series module have been discontinued and are no longer shipping. The maker still publishes specifications and a user guide for owners, and used units are the way players encounter it today.
What tube does the Radial Space Heater use?
It uses 12AX7 tubes, one per channel, driven at a selectable B+ plate voltage of 35, 70 or 140 volts set by the Heat switch. Lower voltages produce more distortion; at the highest 140V setting the tube runs at its optimal power and produces a cleaner signal with even harmonic overtones.
Can you use the Radial Space Heater on guitar?
It is a studio and live-rack device rather than a guitar pedal, with 1/4 inch TRS and D-Sub inputs, but it can run clean or dirty and Radial describes its range as subtle warmth and grit through full harmonic distortion. The Space Heater 500 module adds an OmniPort instrument input when used in a Radial Workhorse rack.
How many rack spaces does the Radial Space Heater take?
The rack unit measures 17.5 inches wide, 6 inches tall and 1.75 inches deep, and weighs 8.5 pounds. Its 6 inch height means it occupies more than a single rack space; the related Space Heater 500 is a single-wide 500 series module instead.
Sources (9)
- Space Heater, Radial Engineering, 2024-08-29
- Space Heater Specifications, Radial Engineering, 2018-05-15
- Space Heater Features, Radial Engineering, 2018-05-15
- Space Heater 500, Radial Engineering, 2023-10-30
- Space Heater 500 Features, Radial Engineering, 2018-05-02
- The Radial Space Heater 500 Tube Overdrive Now Available, Guitar Interactive Magazine, 2015-07-16
- Space Heater 500 FAQ, Radial Engineering, 2018-10-15
- Space Heater 500 Specifications, Radial Engineering, 2018-05-02
- Space Heater, Sushi Box FX
