SPOTFIRE TUBE AUDIO® - SE5
SE5 Single-Ended EL34 Stereo Valve Amplifier Kit
The SpotFire SE5 is a 5-watt single-ended EL34 amplifier designed to deliver the qualities that make classic valve amplifiers enduring: simplicity of signal path, harmonic structure, and musical immediacy — implemented with modern engineering discipline.
At its core is a true single-ended Class-A topology, valued for its natural midrange and direct musical presentation, combined with contemporary refinements for stability, low noise, and predictable performance.
Design Overview
The SE5 is a modern, carefully engineered design valve amplifier kit comprising a two-stage triode Constant Current Draw Amplifier (CCDA) driving a single-ended EL34 output stage.
The circuit has been developed as a complete system, with attention to operating margins, grounding, and long-term reliability — not simply schematic elegance.
Clean Overload Behaviour
The cathode-follower drive stage allows smooth, musical clipping with fast recovery if the amplifier is overdriven.
This is particularly important in low-power amplifiers, where dynamic music peaks can briefly exceed available output power.
Low-Noise Performance
A purpose-designed power supply, DC-powered heaters, and earth-loop breaker resistors work together to minimise hum and noise, making the SE5 well suited to high-efficiency loudspeakers.
Output Stage Operating Modes
The EL34 output stage can be configured for:
Triode
Pentode
Ultralinear
For most users, ultralinear operation provides the best balance of output power and linearity.
When the optional audiophile upgrade is selected, operation is limited to triode or pentode modes, as ultralinear operation is not supported with the upgraded transformers.
Build Options
The SE5 valve amplifier kit is designed to be straightforward to assemble by a competent hobbyist.
Two build options are available:
Solderless kit, supplied with pre-assembled and tested PCBs for a simplified build process
Full DIY kit, allowing builders to populate and solder all components themselves
In both cases, the engineering work has already been done — builders are not expected to design, modify, or troubleshoot undocumented circuits.
Component Quality
The SE5 uses high-quality components selected for electrical performance, reliability, and availability, including:
Audio-grade polycarbonate coupling capacitors
Low-ESR conductive polymer hybrid aluminium electrolytic cathode-bypass capacitors
Gold-pin valve sockets
Large output transformers for controlled low-frequency performance
The printed circuit boards are extra-thick with 2-oz copper tracks to improve durability and thermal performance.
Controls & Connectivity
The front panel features a solid metal volume control and toggle switches for power and input selection, along with a ¼-inch headphone output.
Rear-panel connections include:
Loudspeaker terminals with impedance selector
Feedback on/off switch for operation with or without global negative feedback
Two RCA line-level inputs
A 3.5 mm auxiliary input shared with the second RCA input
A Bluetooth input for streaming from a phone or computer
Audiophile Upgrade Option
An optional audiophile upgrade is available, featuring premium output transformers and Mundorf EVO or Auricap coupling capacitors.
This upgrade provides a noticeable improvement in sound quality when used with high-resolution sources and high-quality loudspeakers.
Ultralinear operation is not supported with this option; triode mode is generally preferred by experienced listeners.
Power Supply & Safety
Mains power does not enter the chassis.
The SE5 uses a fully enclosed, inverter-based high-voltage power supply, with no exposed mains wiring.
The mains power supply complies with applicable Australian safety standards and regulations.
Internal circuitry contains potentially hazardous voltages of up to 280 V DC and must be treated accordingly during assembly and servicing.
Physical Size
The SE5 has a compact footprint suitable for bench or rack placement.
Dimensions:
185 mm (W) × 215 mm (D) × 165 mm (H)
Pricing
The basic SE5 kit (excluding valves) is AUD $1089.
Refer to the shop page for additional options and pricing.
🎧 How Does It Compare to Other Low-Power SE Amps?
| Feature / Design Point | SpotFire SE5 | Typical Budget SE Amp |
|---|---|---|
| Cathode follower driver | ✅ Yes | ❌ No |
| DC heater supply | ✅ Yes | ❌ No (AC heaters) |
| Grid current handling | ✅ Robust | ⚠️ Weak |
| Hum/noise performance | ✅ Very low | ⚠️ Variable |
| Mode switching (triode/UL) | ✅ Yes | ❌ Rare |
| DIY accessibility | ✅ Excellent | ⚠️ Depends |
| Overload behavior | ✅ Smooth, fast recovery | ❌ Often harsh, blocks |
| SE5 model footprint | ✅ Small footprint – suitable for desktops or compact setups | ⚠️ Very large footprint – requires substantial space |