Line Magnetic LM-503PA

Line Magnetic LM-503PA

DUAL Mono-block Audio Power Amplifier

The LM-503PA mono blocs has been created from an original design of Western Electric. It uses a single ended 845 output stage with Full Music 300B drivers. Pre-amplifier stage use a special Line Magnetic tube, the 310A.

The rectifier tube is a 5U3C and the power line is filtered by two special chokes. User bias controls for 300B and 845 are used for bias adjustment with a specific vu meter to allow you to monitor bias with ease.


Point to point hand soldering circuit, the whole machine adopts single copper soldering.
Using high-grade special craft and high quality wide range of EI type single-ended output transformer.
Use 1 high-power Toroidal power transformer per channel.
Preamp stage using the company design and development of 310A vacuum tubes, promote use 300B level.
Power stage using one 845 vacuum tubes do class A single-ended power amplifier.
Power tube current tuning knob and current display meter.
The input has sound balance transformer input and RCA input selection.
High voltage delay when turn on.
Set up big negative feedback loop and small loop negative feedback, to adapt to the different requirements of listening.
Convenient installation drawing plug-in valve cage cover.
Voice is soft, pure and smooth, suitable for appreciation of various types of music.

Power output: 24W +24W(Single-ended class a working condition)
THD: 1%(1kHZ)
Frequency response: 15 hz ~ 35 kHZ (1.5 dB)
S/N Ratio: 87db
Input Impedance: 100kΩ
Output Impedance: 4 Ω, 8 Ω, 16 Ω
Input Sensitivity: 1000 mV
Vacuum Tube: (310A x 1, 300B x 1, 845 x 1, 5U3C x 1) * 2
Power supply: AC 220V (+-5%) (50Hz)
Power Consumption: 290w
Working conditions: temperature: 0 ℃ to 40 ℃ Moisture: 20% ~ 80%
Storage conditions: temperature: – 20 ℃ ~ 70 ℃ Moisture: 20% ~ 90%

Input stage: 1x 310A
Rectifier: 1x 5U3C
Drivers: 1x 300B
Power stage: 1x 845 “Single-ended” and Class A amplifier

Bias control is accessible on top of the amplifier panel with true ampere meter.
Selector NFB min/max
Analog inputs: 1x XLR et 1 RCA
Load impedance for HP to connect: 4/8/16ΩS
SoftStart and time-delay circuit. (30 seconds)
Two EI output transformers with wide bandwidth are applied

Metal and removable tube guard cage

Dimension: W 287 x D 574 x H 279) mm x 2
Net Weight: 32kg x 2 = 64kg
Gross Weight: 34kg x 2 = 68kg

Scroll to Top