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Peter Percival
Guest

Sat Apr 11, 2020 7:45 pm   



Pimpom wrote:
Quote:
On 4/9/2020 10:17 PM, Peter Percival wrote:
Ralph Mowery wrote:
In article <r6nhhe$k81$1_at_news.albasani.net>, peterxpercival_at_hotmail.com
says...

I wish to buy a power supply delivering up to 500V for experiments with
thermionic valves.  What would be a suitable current?



It would be helpful if you would list some of the valves numbers and how

Not yet decided!  Bog standard AF triodes, probably.


I'd love to.  Please point me in the direction of a circuit
diagram.

Maybe you'd like to try this. I used it many many moons ago -
https://www.dropbox.com/s/9dl0o7z33jiqhft/Tube%20preamp%20power%20supply.png?dl=0

Thank you. I'll feed it from a Variac (I have a Bronson) as Phil
Allison suggested.

Phil Allison
Guest

Sun Apr 12, 2020 3:45 am   



Peter Percival wrote:

--------------------------

Quote:
Pimpom wrote:

Maybe you'd like to try this. I used it many many moons ago -
https://www.dropbox.com/s/9dl0o7z33jiqhft/Tube%20preamp%20power%20supply.png?dl=0


** Using two transformers wired like that is a bad idea and will not do what you asked for. The seconds one will be driven into core saturation.


The better way is two identical, 240V to 50 or 60V trannies with windings in SERIES. So the combination is 100/120 to 480V.

Then a Variac drives the low voltage side to easily get 500VDC with NO saturation of any core.




.... Phil

ehsjr
Guest

Sun Apr 12, 2020 7:45 am   



On 4/11/2020 2:12 PM, Peter Percival wrote:
Quote:
Pimpom wrote:
On 4/9/2020 10:17 PM, Peter Percival wrote:
Ralph Mowery wrote:
In article <r6nhhe$k81$1_at_news.albasani.net>, peterxpercival_at_hotmail.com
says...

I wish to buy a power supply delivering up to 500V for experiments
with
thermionic valves.  What would be a suitable current?



It would be helpful if you would list some of the valves numbers and
how

Not yet decided!  Bog standard AF triodes, probably.


 > I'd love to.  Please point me in the direction of a circuit
 > diagram.

Maybe you'd like to try this. I used it many many moons ago -
https://www.dropbox.com/s/9dl0o7z33jiqhft/Tube%20preamp%20power%20supply.png?dl=0

Thank you.  I'll feed it from a Variac (I have a Bronson) as Phil
Allison suggested.


Don't use that circuit - see Phil's reply.
And be aware of the capacitor voltage ratings.
Using 400V filter caps in a 500V supply will
destroy the caps.

Ed

Pimpom
Guest

Sun Apr 12, 2020 9:45 am   



On 4/12/2020 12:13 PM, ehsjr wrote:
Quote:
On 4/11/2020 2:12 PM, Peter Percival wrote:
Pimpom wrote:
On 4/9/2020 10:17 PM, Peter Percival wrote:
Ralph Mowery wrote:
In article <r6nhhe$k81$1_at_news.albasani.net>, peterxpercival_at_hotmail.com
says...

I wish to buy a power supply delivering up to 500V for experiments
with
thermionic valves.  What would be a suitable current?



It would be helpful if you would list some of the valves numbers and
how

Not yet decided!  Bog standard AF triodes, probably.


 > I'd love to.  Please point me in the direction of a circuit
 > diagram.

Maybe you'd like to try this. I used it many many moons ago -
https://www.dropbox.com/s/9dl0o7z33jiqhft/Tube%20preamp%20power%20supply.png?dl=0

Thank you.  I'll feed it from a Variac (I have a Bronson) as Phil
Allison suggested.

Don't use that circuit - see Phil's reply.
And be aware of the capacitor voltage ratings.
Using 400V filter caps in a 500V supply will
destroy the caps.

Ed

The circuit is not intended to produce 500VDC which is not needed
for, in the OP's words, "bog standard AF triodes". 500V far
exceeds the maximum plate voltage of common AF triodes.

230:12 -> 12:230 transformation will theoretically output 230V AC
which, after rectification and filtering cannot exceed 325V, less
in practice. This was suggested for the OP to dabble with as a
first step.

Phil Allison
Guest

Sun Apr 12, 2020 10:45 am   



Pimpom wrote:

--------------------

Quote:

** Using two transformers wired like that is a bad idea and will not do what you asked for. The seconds one will be driven into core saturation.


I used that configuration because small 6- and 12-volt
transformers were easily available at local parts shops and, in
fact, I had them in stock at that time. It worked.



** I do know it can - but no so much at higher currents.

> How will 12V fed to a 12V winding (or 6V to 6V) saturate the core?

** Well, it in fact does.

AC supply transformers are NOT intended to be run backwards.

Take a 15VA, 240V to 6.3V tranny - the off load voltage is gonna be about 7.5V. The gives a turns ratio of 32:1.

On load, 6.3V multiplied by 32 = 201V - so not 240.

Now, the approx 30mA magnetising current has moved from the primary secondary, so multiplied by 32 = 0.96 amps.

In reality you will be lucky to get 180V before rectification, filtering and load.

Been there, done that.


.... Phil

Phil Allison
Guest

Sun Apr 12, 2020 10:45 am   



Pimpom wrote:

------------
Quote:

Ed

The circuit is not intended to produce 500VDC which is not needed
for, in the OP's words, "bog standard AF triodes".


** Fair enough - the OP has been very vague.


Quote:
500V far
exceeds the maximum plate voltage of common AF triodes.


** But not *power* triodes - like the 300B.

They like 700 to 800V.



Quote:
230:12 -> 12:230 transformation will theoretically output 230V AC
which,


** Only IF you use toriodals.

The magnetising current with cheap E-cores will spoil that quite a bit.

Look, I admit have done it myself for a low current, tube pre-amp with a pair of 12AX7 / ECCL83s.

FYI:

I admit I have done many things myself I would never recommend on an internet forum while ever I use my REAL name.

There is so much risk of *misinterpretation* of a seemingly good idea.

One reason being, 500VDC is dangerous, concieveably fatal for anyone with little experience.


BTW I think you are one of the better, more serious posters here.



..... Phil

Pimpom
Guest

Sun Apr 12, 2020 10:45 am   



On 4/12/2020 7:55 AM, Phil Allison wrote:
Quote:
Peter Percival wrote:

--------------------------

Pimpom wrote:

Maybe you'd like to try this. I used it many many moons ago -
https://www.dropbox.com/s/9dl0o7z33jiqhft/Tube%20preamp%20power%20supply.png?dl=0


** Using two transformers wired like that is a bad idea and will not do what you asked for. The seconds one will be driven into core saturation.


I used that configuration because small 6- and 12-volt
transformers were easily available at local parts shops and, in
fact, I had them in stock at that time. It worked.

How will 12V fed to a 12V winding (or 6V to 6V) saturate the core?

Quote:

The better way is two identical, 240V to 50 or 60V trannies with windings in SERIES. So the combination is 100/120 to 480V.

Then a Variac drives the low voltage side to easily get 500VDC with NO saturation of any core.


Better still would be a transformer with 350V and 6.3V/12.6V
secondaries. But such trannies are probably hard to get these
days and be quite expensive. Of course, if the OP still wants to
go for a variable 500V supply, that's up to him.

Note to the OP: The two transformers are connected back-to-back.
The low voltage output of the first transformer is fed to the low
voltage winding of the second transformer. That is, what would
normally be the secondary winding of the 2nd transformer is used
as the primary.

Pimpom
Guest

Sun Apr 12, 2020 12:45 pm   



On 4/12/2020 2:53 PM, Phil Allison wrote:
Quote:
Pimpom wrote:

--------------------


** Using two transformers wired like that is a bad idea and will not do what you asked for. The seconds one will be driven into core saturation.


I used that configuration because small 6- and 12-volt
transformers were easily available at local parts shops and, in
fact, I had them in stock at that time. It worked.



** I do know it can - but no so much at higher currents.

How will 12V fed to a 12V winding (or 6V to 6V) saturate the core?

** Well, it in fact does.

AC supply transformers are NOT intended to be run backwards.

Take a 15VA, 240V to 6.3V tranny - the off load voltage is gonna be about 7.5V. The gives a turns ratio of 32:1.

On load, 6.3V multiplied by 32 = 201V - so not 240.

Now, the approx 30mA magnetising current has moved from the primary secondary, so multiplied by 32 = 0.96 amps.

In reality you will be lucky to get 180V before rectification, filtering and load.

Been there, done that.


... Phil


OK, I'll take your word for it. As I said, I did that "many moons
ago" - decades in fact, and I don't remember the details.

Jeff Layman
Guest

Mon Apr 13, 2020 5:45 pm   



On 12/04/20 10:00, Phil Allison wrote:

Quote:
230:12 -> 12:230 transformation will theoretically output 230V AC
which,

** Only IF you use toriodals.


About right. Over 30 years ago I used back-to-back toroidals to get a
safer supply to a 230V pond pump 10 metres away in the garden.

The matching toroidals were 230:18-21-24-27-30V and rated at 3A. I used
the 30V output of the first, ran it through 10m of 1.5mm^2 cable, and
connected it the 27V secondary of the second toroidal. The pump was
rated at 50W, and, from what I remember, I got about 220V out from the
primary of the second toroidal when under load. It worked that way
without problem for many years.

--

Jeff

Peter Percival
Guest

Wed Apr 15, 2020 6:45 pm   



Peter Percival wrote:
Quote:
I wish to buy a power supply delivering up to 500V for experiments with
thermionic valves.  What would be a suitable current?


So far as making ones own is concerned, I found this
https://www.nutsvolts.com/magazine/article/a-semiconductor-based-high-voltage-utility-power-supply
while looking for something else.

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