GlassWare Audio Design
Thanks for Supporting the Tube CAD JournalNew Balancer PCB and Kit
Simple Tube-Rectified Power Supply
Product Description
The configuration is classic tube power supply: 5Y3 tube rectifier (5AR4 or 5R4 or WE274B could be used), 100-ohm series anode resistors (R1 & R2), and a simple RC filter (R3 & C1/C4). The PCB requires that a center-tapped power transformer be used to establish the B+ voltage. In addition, the PCB requires a 5Vac winding to heat the rectifier. The PS-5 kit includes two high-quality 47µF/450V capacitors (C1 & C2) and three 5W power resistors (R3), 300, 1500, and 10k. (The power resistor can be replaced with a choke by leaving R3 off the PCB and soldering the external choke's two leads to R3's solder pads.) Kit includes user guide and four standoffs, with O-rings and screws.
Many topologies, such as the Aikido and Broskie and White cathode followers or cascode or Aikido topology, use triodes standing atop one another, which makes referencing the heater power supply to the B+ power supply a small chore. With one tube atop another and a single heater power supply, the top and bottom heaters cannot share the same heater-to-cathode voltage relationships. With such totem circuits, the safest path is to reference the heater power supply to a voltage equal to one-fourth the B+ voltage; for example, 75V, when using a 300V power supply. Referencing the heaters to 1/4th of the B-plus voltage ensures that both top and bottom triodes see the same magnitude of heater-to-cathode voltage. The easiest way to establish this voltage relationship is to attach the heater winding's center-tap to the "Heater Ref." pad on the PCB. If the heater winding does not offer a center-tap, then place two 1k resistors in series across the winding and attach the junction between both resistors to the pad labeled "Heater Ref." on the PCB.
Speaking of heaters, where is the heater power supply? There isn't one—well at least not on the PCB. Many power transformers intended for use in tube audio gear are woefully weak in heater winding current. Here is an example, a 6.3Vac @ 1A heater winding cannot deliver anywhere near 1A of DC current at 6.3Vdc. When using such a transformer with a 1A load, it's best to give up on using DC and settle for AC on the heaters. In addition, there is an AC-heater fan club out there, making the PS-5 just perfect for its members. Does not include power transformer.
Many topologies, such as the Aikido and Broskie and White cathode followers or cascode or Aikido topology, use triodes standing atop one another, which makes referencing the heater power supply to the B+ power supply a small chore. With one tube atop another and a single heater power supply, the top and bottom heaters cannot share the same heater-to-cathode voltage relationships. With such totem circuits, the safest path is to reference the heater power supply to a voltage equal to one-fourth the B+ voltage; for example, 75V, when using a 300V power supply. Referencing the heaters to 1/4th of the B-plus voltage ensures that both top and bottom triodes see the same magnitude of heater-to-cathode voltage. The easiest way to establish this voltage relationship is to attach the heater winding's center-tap to the "Heater Ref." pad on the PCB. If the heater winding does not offer a center-tap, then place two 1k resistors in series across the winding and attach the junction between both resistors to the pad labeled "Heater Ref." on the PCB.
Speaking of heaters, where is the heater power supply? There isn't one—well at least not on the PCB. Many power transformers intended for use in tube audio gear are woefully weak in heater winding current. Here is an example, a 6.3Vac @ 1A heater winding cannot deliver anywhere near 1A of DC current at 6.3Vdc. When using such a transformer with a 1A load, it's best to give up on using DC and settle for AC on the heaters. In addition, there is an AC-heater fan club out there, making the PS-5 just perfect for its members. Does not include power transformer.
