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Old 27th December 2017, 04:04 PM   #1
snax is offline snax  United Kingdom
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Default Looking for some power intelligence.

I am looking for a transformer for my next project and i'm having trouble as to how this secondary works:

Secondary SEC I 0 - 275V - 330V / 0,4A

There are other secondary wndings on the transformer but I do not understand this format. Its not a centre tap but is it a tap between 0-330V?

What would you use it for?

Any help appreciated.
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Old 27th December 2017, 04:14 PM   #2
scottjoplin is offline scottjoplin  Wales
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A valve amplifier, is that what you are building?
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Old 27th December 2017, 04:27 PM   #3
snax is offline snax  United Kingdom
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could be.... at 330v it would be the mother of all transistor amps however at 0.4amps, would not be able to pull skin off a custard!
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Old 27th December 2017, 04:28 PM   #4
DF96 is offline DF96  England
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A secondary tap does not have to be at the centre of a winding. You could use it, with the right circuit, to produce two DC voltages - although one of them would only be half-wave rectified so best used for a low current auxiliary supply.
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Old 27th December 2017, 04:47 PM   #5
snax is offline snax  United Kingdom
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But would that not produce unbalanced voltages in the secondary winding due to unsymmetrical currents flowing in the common third connection because of unbalanced loads?
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Old 28th December 2017, 07:47 AM   #6
kward is offline kward  United States
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Another option for that secondary is to use it as either a 275v winding or a 330v winding at up to 400 mA.
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Old 28th December 2017, 10:38 AM   #7
DF96 is offline DF96  England
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Put a bridge (+capacitor) on one set of terminals. Put a single diode (+capacitor) on the other one. Choose correctly and you have a ful-wave rectified main DC supply and a half-wave rectified auxiliary DC supply (which could even be negative, if you want).

Alternatively, just use the voltage you want and ignore the other one.
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Old 28th December 2017, 10:59 AM   #8
snax is offline snax  United Kingdom
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Cheers guy's, It was a new one on me and DF96 you have opened a wealth of new opportunities that I will explore.

Dan
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Old 30th December 2017, 02:59 AM   #9
PRR is offline PRR  United States
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Quote:
Originally Posted by snax View Post
But would that not produce unbalanced voltages in the secondary winding due to unsymmetrical currents flowing in the common third connection because of unbalanced loads?
It can be 275 -or- 330V.

It wants a full-wave bridge, as said.

If you just use the 275V winding, you "waste" about 10% of the copper+iron you paid for. This "waste" is small compared to the benefit of getting closer to your intended DC voltage, which is always partial guess-work due to bad sag in capacitor-input filters and incomplete specification of all parasitics.

Expect either 380VDC or 460VDC. Or less if your load is close to 400mA AC (with cap-input, about 250mA DC).

This PT can power around 50W-60W of tube-amp. 6L6 or EL34 at 4K load, for example.
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Old 1st January 2018, 12:09 PM   #10
snax is offline snax  United Kingdom
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Cheers PRR
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