Luxman: excellence and tradition in HiFi audio

Luxman is one of the most iconic and respected brands in the world of HiFi. Founded in 1925 in Japan, the company has built a solid reputation thanks to the quality, precision, and refined design of its products. Their tube amplifiers, in particular, are considered true jewels of audio engineering, capable of delivering a warm and enveloping sound. Among the most appreciated models are the MQ70 and its “big brother” with additional features, the LX33. The latter is an integrated amplifier that combines a power stage based on the famous MQ70 circuit, a phono RIAA preamplifier, and a tone control section.

The amplifier issue

The Luxman LX33 amplifier was brought to my workshop after a tube replacement carried out by another technician. The customer reported a significant volume imbalance between the two channels and a dull sound on the lower level channel. The situation required an in depth analysis and a methodical approach to identify and solve the problem.

Initial diagnosis: tube testing

To begin, I used the computerized tube curve tracer uTracer to analyze all the tubes, both those installed by the previous technician and the original NOS tubes that the customer had fortunately kept. It became clear that the previous work had been carried out without measurements, with tubes replaced purely by “feel”.

Many NOS tubes in excellent condition had been replaced with modern tubes, possibly not even new, often with unbalanced sections. In particular:

• An ECC85 had been installed that was clearly salvaged from a vintage radio, with a darkened glass envelope and one of the two sections heavily worn, while the original ECC85 was perfect.
• The selection criteria seemed to be based more on aesthetic appearance, shiny getters, rather than objective data, ignoring the fact that dark getters in NOS tubes are a normal characteristic linked to historical materials.

This incorrect choice had compromised the amplifier’s operation, causing part of the reported issues.

Restoring the original tubes and capacitor analysis

After careful selection, I decided to restore almost all the original tubes, with the exception of the four output tubes and one pair of modern ECC83 that I left in the two phono inputs. I then checked the capacitors, focusing mainly on electrolytics and polyester capacitors. While the electrolytics were in good condition, some gray polyester capacitors showed defects typical of Luxman units, with capacitance greatly reduced or completely open. I opted for a full replacement of these components with 1980s era capacitors of comparable quality to the originals. While not “audiophile” parts, they guarantee excellent longevity and stability. The new set of tubes and capacitors restored the coherence and balance necessary for proper amplifier operation.

Final adjustments

After completing the replacement of tubes and capacitors, I carried out all the necessary adjustments:

• Bias and offset
• Driver DC balance

These operations restored the amplifier to full functionality and an impeccable sound.

Technical notes on the LX33

The LX33 is essentially an MQ70 with the addition of a tone control section and a phono RIAA preamplifier. Furthermore, on the rear panel, a jumper between two pairs of RCA connectors allows the power amplifier section to be isolated from the preamplifier section. A significant technical difference concerns the use of ECC82 tubes instead of 6240G in the LX33 and a lower amount of global feedback, which results in a damping factor of about 7 compared to 13 for the MQ70. This value is still excellent, and the reduced feedback contributes positively to sound quality and overall amplifier stability.

Conclusions

Despite the complexity of the work, the LX33 is back to sounding like a true Luxman, once again demonstrating that precision and proper measurement tools are essential for effective repair. I did not include the usual graphs because I did not expect results much different from the MQ70, and because it was Saturday evening and hunger won in the end! ? If you have an amplifier that needs service, contact me, an accurate diagnosis can make all the difference.