Planning to build benchtop 500V tube PSU, help needed.

[Wolfgang]

... in European terms this is the PL519, a powerful sweep often used in linear HF amps.
Quite robust.

Please tell how many mA you need at 500V, because this determines the size of the pass tube(s).

[TERRA Operative]

Cool, I'll check it out.

The article in the OP rates the PSU at 100mA, but the transformer I'll use is good for 200mA (Hammond 374BX)

[Wolfgang]

... OK, so we have to live with 3 tubes (PL519 assumed). One tube can dissipate ca. 35W, assuming we have about 700V of raw rectified voltage we dissipate 70W at 100mA into a short circuit. 3 tubes are safe, with 105W maximum. You will need a fan anyway ...

[TERRA Operative]

Is it easy to add a few more tubes to get closer to the 200mA rating of the transformer, or is there a limitation that caps it at 3 tubes?

[schmitt trigger]

I have seen HV PSUs built with a 6550 tube, far more powerful than a 6AQ5.

The 0A2 regulator tubes have a really nice glow, hope that you can find them. Last time I checked they were in short supply...but you can always go to Akihabara.

EDIT: There is a note on the schematic: SD1 and SD2 are shown in reverse polarity. Mount opposite way.

The way I see it, the diodes are oriented correctly, they are generating a negative voltage for V4's grid. Anyone has a different opinion?

[Wolfgang]

Is it easy to add a few more tubes to get closer to the 200mA rating of the transformer, or is there a limitation that caps it at 3 tubes?

If your transformer is rated for 200mA, this means that the *rectified* current you can draw is about 60% of that. The reason is that

- the rectified current is not sinusoidal, but comes in shorter, high amplitude pulses
- the pulses are not in phase with the voltage.

so the magnetizing effect is very different from a resistive load and that puts more stress on the magnetics.

Result: your 200mA transformer makes a good 100mA PSU with some safety margin.

Recommended literature: Horowitz and Hill Art of Electronics CH. 9

[TERRA Operative]

I have seen HV PSUs built with a 6550 tube, far more powerful than a 6AQ5.

The 0A2 regulator tubes have a really nice glow, hope that you can find them. Last time I checked they were in short supply...but you can always go to Akihabara.

EDIT: There is a note on the schematic: SD1 and SD2 are shown in reverse polarity. Mount opposite way.

The way I see it, the diodes are oriented correctly, they are generating a negative voltage for V4's grid. Anyone has a different opinion?

I'll take a look at those 6550 tubes, I'll check to see what they are worth over here.
It's funny, some common tubes in the States or more often in Europe are hard to get here, but others are super easy. Bit of pot luck sometimes, but substitutes can almost always be found.
I'm about to go on holiday, so it'll be a few weeks before I can make another trip to Akihabara or heat up a soldering iron...

I managed to get myself two 0A2 tubes for $15 the other day, so I'm all set there.  (See the attached pic)
And yep, I saw that note re. the diodes. I'm redrawing the schematic and I got that detail.

I'd be interested in what others think about their orientation too.

If your transformer is rated for 200mA, this means that the *rectified* current you can draw is about 60% of that. The reason is that

- the rectified current is not sinusoidal, but comes in shorter, high amplitude pulses
- the pulses are not in phase with the voltage.

so the magnetizing effect is very different from a resistive load and that puts more stress on the magnetics.

Result: your 200mA transformer makes a good 100mA PSU with some safety margin.

Recommended literature: Horowitz and Hill Art of Electronics CH. 9

Ah-ha, makes perfect sense. I'll dust off my copy of AoE and take a closer look.
Look at me, doing all this learnin'

[schmitt trigger]

Since you will be using this supply to test and prototype tube circuits, you may want to add a pair of 6,3 volt filament supplies.

The way I would do it is with a transformer with dual independent secondaries, such that you can wire them in parallel, series or use them independently.

That would complete your project!

EDIT: And don't forget the NEON indicator lamps. No LEDs please! I would use one as the main AC indicator, and another as the DC output enabled.
Goes without saying that the meters should be analog.

[TERRA Operative]

Yep, I got some 90mm round analogue gauges on the way, and a big red incandescent panel lamp for the 'output on' and an orange neon for 'power switch on'. Old school all the way!  

Good idea on the 6.3v, the schematic shows the 6.3v for the internal tubes as being broken out to the front panel, but I think your idea is better for isolation and decoupling.
I'm sure I can find an appropriate transformer on a shelf somewhere in Akihabara.

[001]

Do You choose flying regulator schematic?

[001]

Hi,

I will post a floating design in a few days, sorry for the delay.

Any news? Please

Best Wishes 

[Wolfgang]

Hi,

I know I am late, but the upcoming holidays dont leave so much time for my hobby.

Anyway, I would like to prod along the schematics in my website below:

https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/a-250v-150ma-variable-linear-power-supply/

This is a true floating design that worked very well (using semiconductors only).

Your PSU has some extra requirements:

- no silicon, glass only - IIRC one of your last comments.
- voltage setting from 0 to 500V
- amps up to 100mA
- foolproof, robust, all components run safely below their maximum ratings.

Consequences are:

- a lot of transformers for the aux voltages plus the heaters (alternative is a custom made transformer for everything in 1 core)
- data will be not as good as the semiconductor design (ripple rejection, stability, out voltage accuracy, ...) .
  It will be perfectly usable for tube circuits, however.

What holds me up the most is getting useful SPICE models of the tubes I wanted to use.

I have started a webpage showing what has been done so far at:

https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/an-all-tube-500v-100ma-regulated-power-supply/

Nice holidays
  Wolfgang

[TERRA Operative]

Wow, awesome work so far! No rush, I'm on holiday too.

A couple silicon diodes in the design would be ok if absolutely necessary, as the original schematic has a few, but transistors are too new-fangled for the 60's style.
I can get a custom transformer made, but if it can be made with an off the shelf transformer/transformers, it'd make it much easier for others to make their own.

I think the simpler, the better. My use case for this is only for powering tube based projects, so looser output parameters for ripple, regulation, etc are fine.

[001]

This is a true floating design that worked very well (using semiconductors only).

Awesome work!

Looks very interesting. Can You tell how it works and why so many TL431 used?

Thanx


UPD : Sorry. Is CNY17 wiring correct at diagram? Is it good idea change 1000pF caps with 100pF? Thanx

UPD2: What the usage difference with Yours awesome second project https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/a-500v-30ma-variable-linear-power-supply/

UPD3: Sorry for my delight and curiosity! Can You post diagram for https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/a-dual-120v200ma-linear-power-supply/ and https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/a-275v-50ma-fixed-linear-power-supply/ ?

UPD4: Does You use supressor diode like reference voltage sourse here? https://electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/a-1kv-50ma-linear-power-supply/

Happy Christmas too!

[coppercone2]

For practical reasons I would use silicon diodes to replace the rectifier tube and zener diodes to replace the voltage reference tube.

The same configuration with a single pass transistor and single transistor error amplifier was common in early power supplies.

careful making parts choices because of heat. I think mr. carlson measured those tube regulators to be something like 90ppm/c and they worked better then a zener diode as a regulator in the tube chassis (as a mod). he warned about this.

I would agree with the silicon diodes.

[TERRA Operative]

Quick bump to let you guys know this is still happening...

Got pretty much all the parts needed (pending final tube choices) except the enclosure (which I'll choose once I know the size I need) and the power transformer and 12H inductor, which I can get from Digikey.

Transformer - https://www.digikey.com/products/en?keywords=hm5128-nd
Inductor - https://www.digikey.com/products/en?keywords=hm4779-nd


Problem is that after the Christmas expenses (airfares and all), I just blew this months allowance on a Tek 577-177 curve tracer, so I'll have to wait a bit to save up my pennies for those last bits.


Anyway, here's a pic of the stuff I have so far.

[coppercone2]

How much cooler does the vacuum insulated part of the tube get when the tube is cooled from envelope reradiation?

Is it possible to measure temperature of the structure with a built in rtd to regulate heater power rather then to cool the tube?

[ArthurDent]

I’ve made some adjustable D.C. power supplies in the past using triodes as the pass element. On the larger supplies I used 6080WA or 6336 tubes. Here are some photos of a small 150-250VDC 100Ma supply I made ages ago that worked pretty well. 

What I’m using now is an electrophoresis power supply made by Bio-Rad that is somewhat similar to the one pictured below. These sell on eBay generally for less than $100. The one pictured has 2 voltage ranges of 250/500VDC and 2 current ranges of 50/500Ma. I needed one a little different so the one I bought has digital meters and goes up to 1Kv.

[001]

I’ve made some adjustable D.C. power supplies in the past using triodes as the pass element. On the larger supplies I used 6080WA or 6336 tubes. Here are some photos of a small 150-250VDC 100Ma supply I made ages ago that worked pretty well. 

What I’m using now is an electrophoresis power supply made by Bio-Rad that is somewhat similar to the one pictured below. These sell on eBay generally for less than $100. The one pictured has 2 voltage ranges of 250/500VDC and 2 current ranges of 50/500Ma. I needed one a little different so the one I bought has digital meters and goes up to 1Kv.

Thanx for great info!
Can You post schematics of this units or correct model numbers to google it?

[TERRA Operative]

Here are some photos of a small 150-250VDC 100Ma supply I made ages ago that worked pretty well. 

Looks cool!
Don't tease us though! You got any schematics?

[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.