Updated 9/29/2024: This page presents series of links and articles regarding power supply construction, safety and other aspects. Please return often as I add more content. Note that I am not an engineer – these are mostly references that I thought were useful and what I’ve learned from 60 years of building power supplies.
Fusing the HV supply (a Littlefuse “white paper”)
Soft Start Ideas for HV Transformers
Soft Start – Step-start; Inrush Current (by W8JI)
Choke Input and Capacitor Input power supplies (by W8JI)
An “Economy” three-voltage power supply by W8JI. On this document, scroll down to the “Full Wave Bridge with Choke” section. The schematic there illustrates the use of a 500-0-500 volt transformer.
The schematic can be reconfigured to generate 2800V (voltage doubler, capacitor input filter), 1400V (capacitor input, full wave), 900V (choke input full wave). In each case, a second voltage of 1400, 700 or 450 volts (i.e., half the full B+ voltage) can also be obtained. R1 feeds the highest HV load, R2 feeds the lower HV load and R3 provides a bias voltage.
Remember that, if a voltage doubler is used, the milliamp capacity of the transformer must be halved since the wattage capability of the transformer remains unchanged no matter what we do to its output voltage.
Older versions of the ARRL Handbook will also have an illustration and explanation of an “Economy Power Supply.”
Balancing (equalizing) resistors for a capacitor bank
The linked article explains how to properly size the resistors used to equalize the voltage across each electrolytic filter capacitor and how to determine what wattage these resistors should be, when two or more electrolytic capacitors are used in series in the power supply.
To the article I would add a reminder that these equalizing resistors are NOT meant to be a “safety” bleeder resistor system although some will use them as such.
They WILL, however, draw some current from the B+ line, acting the same as a safety bleeder does and this should be taken into consideration when figuring how much current will flow through the combined equalizer system and the real safety bleeder, if one is used.
A separate “safety bleeder” resistor, from B+ to ground is often incorporated. Its purpose is that if one of the equalizers fails open, which stops the current draw of that resistor string, the safety bleeder will continue to bleed a small amount of current, and will discharge the filter capacitors when the B+ is turned off. Otherwise the filters will not be discharged for a very long time, which is a safety problem.
In 60 years of building power supplies, I admit I have never experienced a failure of the equalizing resistor string. So perhaps those who argue that a Safety Bleeder is not needed are right? Belt and suspenders?
If a Safety Bleeder is incorporated, and the HV is very high, prevent the B+ from arcing across the safety resistor by using several in series.
For example, a safety bleeder for a 2800 volt supply could consist of five 200K, 5 Watt wirewound ceramic resistors in series (a million ohms). This provides about 3 ma of current to slowly discharge the electrolytics should the equalizer string fail open. The ohm value to use will vary depending on the value of the high voltage and how fast a bleed-down is desired.
A more sophisticated bleed-down scheme includes a relay held open by the AC sent to the HV transformer. When the HV is turned off, the relay closes and connects a 10K ohm high wattage wire-wound resistor from the HV line to ground. This discharges the HV quickly but is more expensive.
Good safety technique includes a handheld discharge stick used to touch the HV line and discharge it to ground through a 10K wire-wound resistor, thus providing a 280 ma drain which should not blow the HV fuse.
And finally, be sure to measure the equalizer and bleeder resistors with an ohm meter before installing them. When constructing my HV supply, I found that one of the new equalizer resistors marked 20K was actually 165K. It might have failed due to heat overload and would certainly have upset the current draw through the string.
A note about electrolytic capacitors: Until modern times, high value electrolytics were not available so choke input filters were used to reduce ripple.
But good quality, high value electrolytics are now available at reasonable cost. Buy the best you can (the 105 degree C ones, not the 85 degree ones), and be generous with the uf value. For example, a string of eight 450 volt, 150uf electrolytics will provide a voltage tolerance of 3,600 volts. The net uf value will be 18.75 uf which is sufficient. If you can find caps with a higher uf rating, use them.
Remember that, with electrolytics run at maximum voltage, the internal leakage current increases greatly, and lifespan might be impacted as internal heat increases. All these are bad things. Do not exceed 75-80% of the voltage rating and the capacitors will run cool, have low leakage current and might last longer than you. So now our 3,600 volt rating is reduced to 0.75 x 3,600 = 2,700 volts. A few more volts won’t hurt but try to stay below 0.8 x 3,600 = 2,880 volts.
Metering an Amplifier (by W8JI)
Multi-Low-Voltage Power Supply for Workbench
Repairing Linear Low-voltage Power Supplies (especially Astons) and circuits to build your own.
QEX Power Supply Article (very complex supply)
High Voltage Power Supplies – Input Chokes, etc
Here is a good zener diode tutorial by Eliott Sound Labs. In addition to the tutorial, it provides a useful table of zener identifying numbers, their characteristics and parameters.
Zeners are noisy things; typically a disc ceramic capacitor mounted as close as possible to the Zener, and parallel to it, is good noise-reduction practice. This link provides good examples of simple noise reduction techniques, using an LM317 regulator as a test bed.
7800 Regulator Series; examples, create
Variable Voltage Supplies, etc. See also the Zener diode information above.
Power Supply Design for Vacuum Tube Amplifiers presents an in-depth tutorial regarding the subject.