PSU designer understanding.

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Nick
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#16 Re: PSU designer understanding.

Post by Nick »

Probably wrong, but without a shared core would the load on one transformer not alter the voltage from the other one and vice versa?
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Paul Barker
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#17 Re: PSU designer understanding.

Post by Paul Barker »

Nick wrote: Wed Apr 29, 2020 10:42 am Probably wrong, but without a shared core would the load on one transformer not alter the voltage from the other one and vice versa?
Yes which you’d mitigate by selecting power rating for the adjustment transformer selecting it’s capaility for it’s share of the ac mains, roughly speaking to get Phil’s 3kvct transformer reduced to 2kvct I’ve assumed its a 1 to 1.5kva device we’d need a 300 to 500 watt device.

For Phil : The secondary voltage of the isolation transformer shows 80 instead of 110 or 120 which it would normally provide, as it only see’s a proportion of the ac mains. So actual windings across mains 110 + 240. So 110/350 means it shares .314 of entire mains voltage .314 x 240 = 75v
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#18 Re: PSU designer understanding.

Post by Nick »

Yes, but in that example would you not need to be actually pulling 400W out of the second transformer, or the same percentage of 400w as you are pulling from the 1kva transformer. If for whatever reason the load on the smaller transformer disappeared (say not having valves in) the larger transformer would output full voltage with unfortunate results.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#19 Re: PSU designer understanding.

Post by Paul Barker »

Paul Barker wrote: Wed Apr 29, 2020 10:54 am
Nick wrote: Wed Apr 29, 2020 10:42 am Probably wrong, but without a shared core would the load on one transformer not alter the voltage from the other one and vice versa?
Yes which you’d mitigate by selecting power rating for the adjustment transformer selecting it’s capaility for it’s share of the ac mains, roughly speaking to get Phil’s 3kvct transformer reduced to 2kvct I’ve assumed its a 1 to 1.5kva device we’d need a 300 to 500 watt device.

For Phil : The secondary voltage of the isolation transformer shows 80 instead of 110 or 120 which it would normally provide, as it only see’s a proportion of the ac mains. So actual windings across mains 110 + 240. So 110/350 means it shares .314 of entire mains voltage .314 x 240 = 75v
edit, it actually workes out at 75v not 80v so my drawing marked wrong.

This leaves many options, if you get a dual primary transformer for use on 120/240 or 110/220 then you can use one of the primary winding across the mains the other as the secondary and now you can select secondary built in voltages to assist you with filaments. For example a 20v secondary would provide 6.3v at the 0.314 factor.
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#20 Re: PSU designer understanding.

Post by Paul Barker »

Nick wrote: Wed Apr 29, 2020 11:00 am Yes, but in that example would you not need to be actually pulling 400W out of the second transformer, or the same percentage of 400w as you are pulling from the 1kva transformer. If for whatever reason the load on the smaller transformer disappeared (say not having valves in) the larger transformer would output full voltage with unfortunate results.
It isn’t in a linea relationship but there would require some adjustment. This method isn’t something new, it was common practice, and a good wya to pic off additional supplies. were not reinventing the power supply, we’re harnessing a known technique so we don’t over think it. I know thta you have a much more analytical mind which can take youre designs to the extreme excellence you achieve.
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pre65
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#21 Re: PSU designer understanding.

Post by pre65 »

Thanks Paul / Nick. I appreciate the efforts you make to help me. :)

I think that it's going to be a LOT simpler for me just to get another couple of big toroids, so It will be like it was before but just another 200-250V HT.

I reckon a 1KV toroid will do the job.

The Hammond 735A transformers are £445 EACH from Mouser, so if I can sell them on at some time in the future that would be very good. :wink:

The reason I got those Hammonds (and 4 X 833C + box of U19 and 833 bases and top caps) was when Phil Ramsey was short of cash and he "persuaded" me that they were right for the job. They probably are if you want HT around 1800 - 2000V.
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#22 Re: PSU designer understanding.

Post by Paul Barker »

Nick wrote: Wed Apr 29, 2020 11:00 am Yes, but in that example would you not need to be actually pulling 400W out of the second transformer, or the same percentage of 400w as you are pulling from the 1kva transformer. If for whatever reason the load on the smaller transformer disappeared (say not having valves in) the larger transformer would output full voltage with unfortunate results.
Not in extremis. It would alter numbers a little but not linearly neither precipitating dramatic outcome. All adjustable on test.
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#23 Re: PSU designer understanding.

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I know thta you have a much more analytical mind
Not that, I am just concerned that Phil doesn't get into something that will surprise him and not in a good way.
Little known fact, coherent thought can destructively interfere with itself leaving no thought at all, that’s why I prefer incoherent thought.
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#24 Re: PSU designer understanding.

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Yes I know, I anticipated he’d not adopt my suggestions. But it doesn’t harm to give people the opportunity to see how to overcome such obstacles.
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#25 Re: PSU designer understanding.

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Yes I know, I anticipated he’d not adopt my suggestions.
You don't have any views on injecting bleach do you :-)
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#26 Re: PSU designer understanding.

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pre65 wrote: Wed Apr 29, 2020 11:35 am Thanks Paul / Nick. I appreciate the efforts you make to help me. :)

I think that it's going to be a LOT simpler for me just to get another couple of big toroids, so It will be like it was before but just another 200-250V HT.

I reckon a 1KV toroid will do the job.

The Hammond 735A transformers are £445 EACH from Mouser, so if I can sell them on at some time in the future that would be very good. :wink:

The reason I got those Hammonds (and 4 X 833C + box of U19 and 833 bases and top caps) was when Phil Ramsey was short of cash and he "persuaded" me that they were right for the job. They probably are if you want HT around 1800 - 2000V.
Can’t justify bidding for your hammonds, I already have enough boatanchor transformers. They all have to have their voltages brought down one way or another.
Last edited by Paul Barker on Wed Apr 29, 2020 1:54 pm, edited 1 time in total.
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#27 Re: PSU designer understanding.

Post by pre65 »

Paul Barker wrote: Wed Apr 29, 2020 1:38 pm Yes I know, I anticipated he’d not adopt my suggestions. But it doesn’t harm to give people the opportunity to see how to overcome such obstacles.
Thanks again for taking the trouble to offer assistance. To my simple mind the solution was too complicated, but then I'm not in your (or Nicks) league for knowledge in our hobby.
Life is what happens to you while you're busy making other plans. John Lennon

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#28 Re: PSU designer understanding.

Post by Paul Barker »

You are in my league, I only know simple stuff, anyone could understand what I know that has managed to sustain life on earth, unless their letting others carry them.

It really is all very simple when broken down.
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#29 Re: PSU designer understanding.

Post by pre65 »

Paul Barker wrote: Wed Apr 29, 2020 1:51 pm
Can’t justify bidding for your hammonds, I already have enough boatanchor transformers. They all have to have their voltages brought down one way or another.
I got them at a reduced price from Philip Ramsey (for several reasons I'd rather not explain) so if anyone was interested there is deffo a deal to be done. :wink:
Life is what happens to you while you're busy making other plans. John Lennon

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#30 Re: PSU designer understanding.

Post by Paul Barker »

What are you planning to order as a replacement? Any links?
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