The Amplimo 55PP4K5H is a wide-bandwidth toroidal tube output transformer for push-pull amplifier designs, featuring a 4.5 kΩ primary impedance, 0-4-8 Ω secondary taps, 35% UL taps, and a nominal power rating of 55 W.
Amplimo 55PP4K5H Output Transformer Push-Pull 25 Watt Wide bandwidth toroidal tube output transformer
The Amplimo 55PP4K5H is designed for tube amplifiers using a push-pull output stage. Its primary impedance is 4.5 kΩ, while the secondary side provides 0, 4 Ω, and 8 Ω connections. The transformer uses clearly defined lead colours for anode, B+, ultra-linear taps, and speaker outputs, supporting clean integration into suitable amplifier builds.
Performance is centred on wide bandwidth and controlled magnetic behaviour. The transformer offers a -3 dB frequency bandwidth of 7 Hz to 95 kHz, with power bandwidth starting at 19 Hz. Electrical characteristics include 1150 H primary inductance, 7 mH primary leakage inductance, and 580 pF primary capacitance.
The 55PP4K5H includes 35% ultra-linear taps, provided via the green and grey leads. If these UL leads are not used, they must be insulated carefully with heatshrink. The secondary taps are intended to be used one at a time, and the white wires must always be connected together, as must the black wires.
Mechanically, this transformer is potted in a black textured aluminium shell for a robust finish. It measures 126 mm in diameter and 66 mm in height, uses an M8 x 20 centre bolt for mounting, has 200 mm lead lengths, and weighs 2.6 kg. Its format makes it a specialised choice among high-quality audio components for tube amplifier construction and service work.
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