Monoblock MA15 Mk 2 Early

The Radford MA15 series of amplifiers was a well-regarded line of vacuum tube audio amplifiers produced in the 1960s.

There were four versions:

1. MA15 Mk1: This was the original version of the amplifier.
2. MA15 Mk2 Early: An updated version of the original design.
3. MA15 Mk2 Late: A further refinement of the Mk2 design.
4. CMA15: This was a kit version of the MA15 amplifier.

The Radford MA15 Mk2 Early Monoblock was an improved version with significant enhancements:

• Output power: 15 watts (maintained)
• Circuit design: Revised for better performance
• Phase inverter: Changed to pentode-triode configuration
• Feedback: Increased to 27dB of negative feedback
• Output transformer: Improved design with first resonance at 150kHz
• Input stage: Added step network for high-frequency stability
• Feedback network: More complex R/C step network across the feedback resistor
• Performance: Significantly lower distortion, especially at high frequencies
• Power delivery: Able to deliver rated power up to 20kHz
• Phase shifts: Reduced at high frequencies
• Stability: Carefully tuned for stability with higher feedback

The Mk2 version demonstrated substantial performance improvements, particularly in distortion reduction and power delivery across a wider frequency range.

Output Transformers
The key difference between the output transformers of the Radford MA15 Mk1 and Mk2 models lies in their design and performance characteristics:

Radford MA15 Mk1 Output Transformer

• Resonance Frequency: The Mk1 output transformer had a first resonance around 60-70kHz.
• Performance: This design resulted in higher phase shifts and distortion at high frequencies, limiting its ability to deliver full power at the upper end of the audible spectrum.
• Design Complexity: The transformer was less advanced, which contributed to reduced stability and slightly inferior sound quality compared to the Mk2.

Radford MA15 Mk2 Output Transformer (T2063)

• Resonance Frequency: The Mk2 output transformer was significantly improved, pushing its first resonance to approximately 150kHz.
• Performance: This allowed for reduced phase shifts, better high-frequency stability, and lower distortion across the frequency range. It also enabled the amplifier to deliver its rated power up to 20kHz.
• Design Complexity: The improved design contributed to a more refined sound and greater technical performance, addressing the limitations of the Mk1.

These enhancements in the Mk2's output transformer were a critical factor in its superior performance compared to the Mk1.

Hier finden Sie 32 Modelle, davon 25 mit Bildern und 10 mit Schaltbildern.
Alle gelisteten Radios usw. von Radford Electronics Ltd.; Bristol