Electronics > Projects, Designs, and Technical Stuff
Planning to build benchtop 500V tube PSU, help needed.
ArthurDent:
When I made my 150-250VDC 100ma power supply I was trying to use parts I had in my junk box while still making a good regulated power supply. The case was from a military surplus magnetic amplifier and the case was the only part of that unit that was useful to me. I didn’t have one transformer that would work but I did have 2 identical smaller transformers that would fit perfectly in the back part of the case and give me the voltages and current I was looking for if I wired the HV windings in parallel. I did buy new meters and to give you an idea how old this is, I bought them from Lafayette Radio Electronics (kind of like Radio Shack) who went out of business in 1981! The circuit I used was one I modified from one I saw in an HP manual from about that time period.
The voltmeter was modified to have an expanded range by using a 150V Zener and using a series resistor to make the meter really read 0-100 volts and then marking the dial to read 150-250 volts. If you’re wondering why there is a 1N4007 between the output and the meter, that is to prevent meter damage if the output somehow dropped to zero, effectively putting 150 volts on the meter in the reverse direction. The milliamp meter is the same basic movement as the voltmeter with the series resistor removed and a shunt resistor in parallel and the scale marked in Ma.
One of the transformers 6.3 volt windings is used for the heater supply for the tubes and not referenced to ground to eliminate any heater to cathode voltage problems. The other 6.3 volt winding is connected to terminals on the back of the case to power tube heaters in devices I might be constructing.
The capacitor from the supply output to the pot wiper eliminates the D.C. component but sends the outputs a.c. ripple voltage unattenuated to the error amplifier. Instead of using a 5651 gas reference tube like the original design I used a 82 volt Zener that gets its supply voltage from the regulated output. It feeds the reference voltage to the error amplifier through the triode section of the 6U8A used as a cathode follower. Where I didn’t use the 5651, the triode might not be needed and the Zener could probably supply enough current to be connected between the error amplifier cathode and ground, then I could replace the 6U8A with just a 6AU6 pentode. The 6BX7 has a maximum plate voltage rating of 600VDC so it is used within its specs.
The HV rectified output from the two 1N4007 diodes is connected to the two 40 mfd electrolytics through a 10 ohm resistor that lessens the surge current and is also an emergency fuse. The two deck power switch is three position non-shorting and in the off and standby positions there is a 6.8K resistor connected from the two 40 mfd electrolytics to ground to safely discharge them. This capacitor has a 500 VDC rating because with no load there is about 450 volts on this capacitor. When the switch is in the operate position the 6.8K drain resistor is switched off and the HV center tap is connected to ground and the output is present.
I didn’t have a schematic so I had to trace it out and that took me a while but here it is. Hopefully I didn’t miss anything.
Circlotron:
For the front end I'd suggest a voltage doubler with two 400VDC caps in series. Big ones are very available nowadays. Depending on the cap size you may not even need to use a filter choke. Silicon diodes of course. And seeing the transformer would only need a single winding you have lots more to choose from!
TV horizontal output tubes might be a good choice for the series pass reg, depending on price of course. They can have relatively low voltage drop when fully on.
Sylvi:
Hi
The supply linked by the OP is not good for testing tube power amps as it only has 100mA. Preamps okay. A 10W amp with 10k OT primary will tax this PSU. A typical 50W amp with 4k load needs 300mA peak. A "dead" amp usually has a PSU and in most cases the thing is not dead is the PT. Repair and troubleshooting must be handled with common sense.
What do you actually want to do?
If you are building tube amps, they have a matched PSU, which you build and test first and always power new builds or suspect amps through a Power Limiting Safety Socket - light bulbs not variac.
500V electrolytic caps are not a problem to acquire, just look at Digikey or Mouser. If you need higher than 600V, you have to either place caps in series with parallel bleeder resistors to enforce voltage sharing, or use plastic caps. You can get high values at high voltages in plastic, as they are used for DC links between incoming PSUs and point-of-use regulators. They are quite compact considering they have esssentially unlimited life expectancy.
Unless you really want to build the tube PSU for fun or experience, there is no benefit to it being tubes versus solid-state. About the only benefit tubes offer is that they do not need heat sinks although they still need heat to be removed to be reliable.
001:
Any news? I`m electrified with this tread ::)
schmitt trigger:
Arthur:
Two thumbs up for your supply design! :-+ :-+ No, three thumbs up. :-+ :-+ :-+
I would only have kept the gas regulator tube instead of the zener, because, you know...........the nice glow.
But I understand the choices you made. Zeners were less expensive than gas tubes, were less prone to motorboating, and back in those days having "hybrid" circuits were considered the path forward.
The same can be said of the 1N4007 diodes versus -let's say- a 5U4.
Thanks for taking the time to share your circuit.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version