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

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Wolfgang:

--- Quote from: TERRA Operative on December 17, 2018, 05:31:29 pm ---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?

--- End quote ---

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:

--- Quote from: schmitt trigger on December 17, 2018, 05:34:51 pm ---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?


--- End quote ---

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.  :-/O (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.




--- Quote from: Wolfgang on December 17, 2018, 05:43:39 pm ---
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


--- End quote ---

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' :D

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! :D  :-/O

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?

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