Versatile Power Supply Design
This power supply, originally crafted for the ‘Simple hybrid amp’ featured in another section of this issue, proves versatile for various applications. Employing a cascade generator for 170 V, a switch mode supply for 16 V, a series regulator for 12 V, and a dedicated transformer for 6.3 V filament supply, this design caters to diverse power needs. The choice of LT1074CT (IC1) as the regulator allows the circuit to be assembled with standard components, ensuring high efficiency.
Optimizing Efficiency and Power Loss
Compared to a linear voltage regulator, this device exhibits lower power loss, enabling the utilization of a higher transformer voltage and a reduced cascade section for generating the critical 170 V needed for the SRPP stage in the amplifier. The decreased input current also minimizes losses in the bridge rectifier (D1 to D4). A conventional 12 V regulator (IC2) transforms the 16 V into a stable voltage for the buffer stage, showcasing an efficient use of power.
Overcoming Filament Voltage Challenges
In cases where an ECC83 (12AX7) is employed in the hybrid amp, the 12 V output could potentially power the valve’s filaments, despite the ideal requirement of 12.6 V. This design adaptation demonstrates flexibility, accommodating different valve configurations while addressing specific voltage needs, making it a practical choice for various applications.
Optimizing Valve Current with Heatsinks
To accommodate the valve’s current demand of approximately 150 mA, the 12 V regulator necessitates a heatsink. A suitable choice is the small version of the SK129 heatsink from Fischer (38.1 mm, 6.5 K/W). Additionally, diode D7, integrated into the ground connection of the regulator, can be utilized to raise the voltage by 0.6 V. Closing JP1 shorts D7, ensuring a stable 12 V output. For effective cooling of IC1 and D5, the 63.5 mm version of the SK129 heatsink (4.5 K/W) suffices, mounted on opposite sides while ensuring electrical isolation from each other and the heatsink.
Component Choices and Filtering Strategies
Standard chokes rated at 5 A can be employed for L1 and L2. The bridge rectifier diodes (B10100) are Schottky rectifiers with a low forward voltage drop. Opting for diodes with a reverse voltage rating of 100 V offers the flexibility of using an LT1074HVCT, compatible with input voltages up to 60 V. The cascade circuit, generating the HT supply for the valve, is powered by an 80 VA transformer, producing nearly 170 V. L3 and C22 serve to filter out any high-frequency interference originating from IC1. For heavier loads, a smaller cascade circuit coupled with a higher transformer voltage and LT1074HVCT usage is recommended.
Generating Filament Voltage and Channel Considerations
The filament voltage is derived from a 4.5 VA transformer, providing approximately 6 V, close to the required 6.3 V. Alternatively, specialized transformers or stabilized 6.3 VDC supplies can be utilized, allowing user preference to dictate the choice. While the supply theoretically supports two channels, employing an ECC88 in the amplifier might necessitate individual cascade generators for each channel. Careful consideration of these factors ensures efficient and reliable operation of the circuit.