Mesa/Boogie Son Of Boogie Amplifier Repair

Customer Complaint

The owner brought this Mesa/Boogie Son of Boogie (SOB) into the shop after attempting to use it for the first time following a long period of storage.

Upon powering the amplifier up, it produced significant noise and loud popping sounds. The customer requested a full inspection and restoration to return the amplifier to reliable operating condition.

About the Mesa/Boogie Son of Boogie

The Mesa/Boogie Son of Boogie, commonly known as the SOB, was a 60-watt combo amplifier produced between 1982 and 1985.

Designed as a more affordable alternative to the highly successful Mesa/Boogie Mark I series, the SOB retained the same powerful 6L6 output section while utilizing a simpler preamp design.

The amplifier features two cascaded input channels with independent volume controls, allowing for a wide range of gain settings. Unlike many Mark Series amplifiers, the SOB does not include a graphic EQ section. Instead, it incorporates a "Limit" control which functions as a master volume.

Although physically compact, the Son of Boogie is built exceptionally well and is surprisingly heavy for its size. It is also capable of producing impressive volume levels comparable to much larger amplifiers such as a Fender Twin Reverb.

Initial Inspection

Externally, the amplifier was in excellent cosmetic condition.

However, knowing that the amplifier had been stored unused for an extended period immediately raised concerns regarding the condition of the power supply electrolytic capacitors.

Electrolytic capacitors contain a liquid electrolyte that naturally degrades over time. Long periods of inactivity can accelerate this aging process, increasing the risk of capacitor failure when power is reapplied.

For this reason, I always recommend having vintage tube amplifiers inspected by a qualified technician before powering them up after years of storage.

Diagnostic Process

After removing the chassis from the cabinet, the source of the customer's complaint quickly became apparent.

One of the leads connected to a primary power supply filter capacitor had broken, resulting in unstable power supply filtering and causing the excessive noise and popping heard during operation.

Further inspection revealed that all five of the main power supply filter capacitors were original to the amplifier and had reached the end of their expected service life.

While capacitor lifespan varies depending on operating conditions and manufacturing quality, power supply electrolytic capacitors in vintage tube amplifiers are often considered candidates for preventative replacement after approximately 15 to 20 years of service.

Even if an amplifier appears to function normally, aging filter capacitors can eventually fail and potentially cause additional damage to surrounding circuitry.

Restoration and Repair

A complete set of replacement power supply filter capacitors was sourced, carefully matching the original capacitance and voltage specifications.

Before beginning any work, all stored high voltages were safely discharged from the amplifier. Tube amplifiers can retain potentially lethal voltages long after being switched off, making proper safety procedures essential.

The original filter capacitors were then removed and replaced with high-quality modern components.

While the chassis was open, all solder joints were inspected, and the controls were cleaned and lubricated to eliminate oxidation and ensure smooth operation.

After reassembly, the amplifier was thoroughly tested under operating conditions. The power supply was stable, the unwanted noise and popping were eliminated, and the amplifier was returned to reliable working condition.

Repair Summary

Symptoms

• Excessive noise

• Loud popping during operation

• Long-term storage without use

Work Performed

• Power supply inspection

• Replacement of all power filter capacitors

• High-voltage safety discharge

• Solder joint inspection

• Control cleaning and lubrication

• Full operational testing

Results

With a rebuilt power supply and preventative maintenance completed, this Mesa/Boogie Son of Boogie is once again operating as intended and ready for many more years of service.

Vintage tube amplifiers can often remain reliable for decades, but periodic maintenance of aging components such as electrolytic capacitors is essential to preserving both performance and long-term reliability.

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