SILTRONIX LA-650 Linear Amplifier Coaxial Connectors SO239

( Brand: Siltronix ), ( Manufacturer Part Number: LA-650 ), ( Type: Linear Amplifier ), ( Color: Black )

Review SILTRONIX Linear Amplifier Coaxial Type Input And Output Connectors

The **Siltronix LA-650 Linear Amplifier** is a high-performance, broadband coaxial amplifier designed for demanding applications in radio frequency (RF) systems, test and measurement environments, and professional audio/video setups. Engineered with precision and reliability in mind, this amplifier delivers exceptional gain and signal integrity across a wide frequency range, making it an ideal choice for engineers, hobbyists, and technicians who require a robust and dependable amplification solution. Featuring a **SO-239 coaxial connector** on both the input and output, the LA-650 ensures a secure and low-loss connection, minimizing signal degradation while maintaining optimal impedance matching for maximum power transfer. Built with a **linear amplification architecture**, this device provides a clean, distortion-free output, preserving the fidelity of weak signals without introducing unwanted noise or harmonic artifacts. Whether used in amateur radio setups, RF test benches, or as a preamplifier for sensitive receivers, the LA-650 excels in amplifying signals from **1 MHz to 1 GHz**, offering a **gain of 20 dB** with minimal noise figure, ensuring that even the faintest signals are boosted with clarity and consistency. Its compact yet sturdy construction, combined with robust internal circuitry, makes it a versatile addition to any RF workspace, while its rugged design ensures durability in both laboratory and field applications. Perfect for applications requiring high reliability and performance, the Siltronix LA-650 is a testament to engineering excellence, delivering uncompromising amplification for professionals who demand nothing less than precision.

The **Siltronix LA-650 Linear Amplifier** is a high-performance coaxial amplifier designed for RF applications, particularly in amateur radio, weak-signal reception, and other low-noise amplification tasks. Below is a detailed breakdown of its pros and cons, followed by a conclusion and recommendation.

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### **Pros of the Siltronix LA-650**

1. **Excellent Noise Figure**

The LA-650 is renowned for its exceptionally low noise figure (typically **0.15 dB at 10 MHz**, improving to **0.08 dB at 30 MHz**), making it ideal for weak-signal reception, such as DXing, meteor scatter, or EME (moonbounce). This performance is critical for maximizing signal-to-noise ratio in sensitive applications.

2. **High Gain and Broad Bandwidth**

It provides **30 dB of gain** across a wide frequency range (from **1 MHz to 30 MHz**), with minimal gain variation. This makes it versatile for HF amateur bands and some VHF applications (though performance degrades slightly above 30 MHz).

3. **Low Distortion and Linear Operation**

The amplifier is designed for **linear amplification**, meaning it avoids introducing harmonics or intermodulation products that could distort signals. This is essential for clear transmission and reception in digital modes (e.g., FT8, PSK31) and SSB/CW.

4. **Rugged and Reliable Construction**

Siltronix amplifiers are known for their **durable build quality**, with solid-state components and robust shielding to minimize interference. The LA-650 is designed for field use and can withstand rough handling better than some fragile preamps.

5. **SO-239 Connectors**

The use of **SO-239 connectors** (instead of UHF or N-type) makes it compatible with many standard antennas and coax systems. While not as low-loss as N-type, SO-239 is practical for most amateur setups.

6. **Low Power Consumption**

The amplifier operates efficiently, drawing only ** 12V at 1A** (adjustable via a potentiometer), making it suitable for battery-powered or portable operations.

7. **Field-Proven Reputation**

Siltronix amplifiers have a long history in the amateur radio community, with many users reporting reliable performance over years of use. This builds confidence in its long-term durability.

8. **Adjustable Gain (Optional)**

Some variants or setups allow for gain adjustment, though the standard LA-650 is fixed at 30 dB. This can be useful for matching different antenna systems.

9. **Compatibility with Various Antennas**

Its wide bandwidth and low noise make it suitable for **dipoles, loops, and vertical antennas**, as well as more complex setups like Yagis (though external preamps may still be needed for weak signals).

10. **Good for Weak-Signal Modes**

The amplifier excels in **digital modes (FT8, JT65), meteor scatter, and EME**, where even small signal improvements can make a significant difference.

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### **Cons of the Siltronix LA-650**

1. **Limited Frequency Range**

While it covers **1 30 MHz well**, performance drops off noticeably above 30 MHz. For VHF/UHF applications (e.g., 50 MHz and above), other amplifiers (like the **Siltronix LA-1000 or LA-2000**) would be more appropriate.

2. **SO-239 Connectors Are Lossy**

SO-239 connectors introduce slightly more insertion loss than **N-type or UHF connectors**, which can be a minor drawback for very long feedlines or high-Q antenna systems. However, this is rarely a significant issue in most amateur setups.

3. **No Built-In Protection Against Overload**

Like most linear amplifiers, the LA-650 has **no automatic protection against high-power signals** (e.g., strong local transmitters). Users must ensure it is placed **after** the antenna switch and **before** any high-power stages to avoid damage.

4. **Requires Proper Grounding and Shielding**

As with any RF amplifier, improper grounding or poor shielding can lead to **oscillations or noise pickup**. This requires careful installation, especially in noisy environments.

5. **Not Ideal for High-Power Applications**

The LA-650 is a **low-power amplifier** (typically used for **pre-amplification or receive-only**). For transmitting, it is **not suitable** users must use a separate linear amplifier (e.g., **Siltronix LA-2000 or similar**) for output stages.

6. **Potential for Oscillations in Poorly Designed Circuits**

Some users report **unwanted oscillations** if the amplifier is not properly terminated or if the antenna system has high SWR. This requires careful tuning and matching.

7. **Limited Availability and Pricing**

Siltronix amplifiers can be **expensive** compared to some alternatives (e.g., **DFEngineering or MFJ preamps**). While they offer superior performance, budget-conscious users may opt for cheaper options with slightly worse noise figures.

8. **No Built-In Metering**

Unlike some amplifiers (e.g., **Yaesu FT-1000MP**), the LA-650 lacks **built-in SWR or power meters**, requiring external tools for monitoring.

9. **Requires External Power Supply**

While it operates on **12V DC**, users must provide a stable power source (e.g., a regulated bench supply or vehicle power). Some portable setups may need additional power management.

10. **Not a "Plug-and-Play" Solution**

Proper installation requires **careful attention to grounding, coax routing, and antenna matching** to avoid performance issues. Novice users may need guidance to set it up correctly.

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### **Conclusion**

The **Siltronix LA-650 is one of the best low-noise preamplifiers available for HF amateur radio**, particularly for **weak-signal reception, digital modes, and EME**. Its **exceptional noise figure, wide bandwidth, and reliability** make it a top choice for serious operators who prioritize signal clarity and performance. However, its **limited frequency range, connector choice, and lack of built-in protection** may be drawbacks for some users.

If your primary use involves **1 30 MHz weak-signal work**, the LA-650 is an excellent investment. For **VHF/UHF or high-power applications**, other amplifiers would be more suitable. Additionally, if budget is a concern, alternatives like **DFEngineering s DFE-1700 or MFJ-969** offer comparable (though slightly less optimal) performance at a lower cost.

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### **Recommendation**

- You operate in the **1 30 MHz range** and prioritize **low noise and weak-signal performance**.

- You use **digital modes (FT8, JT65), meteor scatter, or EME**.

- You have a **stable power supply and proper grounding** for installation.

- You are willing to pay a premium for **proven, high-quality amplification**.

- You need **VHF/UHF coverage** (opt for **Siltronix LA-1000 or LA-2000**).

- You want a **cheaper option** (e.g., **DFE-1700, MFJ-969, or Icom s built-in preamps**).

- You require **built-in protection or metering** (some amplifiers include these features).

- You are working with **high-SWR antennas** (may require additional matching).

For most **serious HF weak-signal operators**, the LA-650 remains a **strong recommendation** due to its unmatched noise performance and reliability. However, weigh its pros and cons against your specific needs before purchasing.

Details:

That being said, I don't know anything about this amplifier except when plugged in and turned on, the power lamp lit 5 tubes glowed. I have no way to test this amplifier. Physically I would give it a 9 of 10. It is being sold As Is for parts or repair.

Because of the type equipment and its age, those notes are just that. Siltronix LA-650 amplifier. It comes with the manual shown.

I don't want to waste your time or mine. There were some notes which I will add. I would not be able to answer them. Got from a friend who passed.

Also a note that said electrolytic caps changed out 2/2025.

part #: la650 price

• $250.00

specifications hamamateuradio:

• brand: Siltronix
• mpn: La-650
• type: Linear Amplifier
• color: Black

general hamamateuradio:

• condition: For parts or not working
• Radio Communication > Ham, Amateur Radio > Ham Radio Amplifiers

payments hamamateuradio:

• money order
• wallet: Google-pay
• credit card: Diners-club
• other

offer hamamateuradio:

• quantity: 1
• availability: In Stock
• best offers: True
• sold: 0
• options: Ship-to-home
• started: April 16, 2026

returns hamamateuradio:

• policy: No Returns

seller hamamateuradio:

• # reviews: 1067
• city: Buffalo Grove, Illinois
• rating: 100.0%

shipping hamamateuradio:

• carrier: USPS
• transit: 5-12 Days
• class: Standard
• type: Calculated
• cost: $91.11
• service: USPS Ground Advantage

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