Transformer question - 110 v and 25 v from 1 secondary?

Brit01 · 24th August 2010, 03:57 PM

Thinking about providing 2 supplies from 1 tranny.

I can get a step down tranny 220/110 with 1000 watts supply.

Could I run ~120 volts 300mA and also a 25V 3.5 Amp from this 1 amp?

If I calculate correctly:

1000/110= 9 Amps available

How would I drop 110/120 volts to 25V to supply 3 amps from this tranny?

I use PSUII to do simple circuits but never attempted to take off a tap at a much lower voltage with much higher current.

TheGimp · 24th August 2010, 04:03 PM

Thats a big transformer. You will get about 150-170V if you full wave rectify it.

To get the 25V at 3A you have several options:

(1) linear regulator = lots of power dissipation (maybe 500W continuous).

(2) Switching Regulator = better efficency with the risk of noise

(3) inductor input filter = lots of cost for the iron 20H 3A is a big choke!

Cheaper to get the right transformer(s) to begin with.

Brit01 · 24th August 2010, 04:25 PM

Thanks Gimp.

There is also a 500w version. More manageable giving about 4.5 amps.

I can't get a 25v 3.5 amp tranny here.
Even difficult to get a 12V more than 1 amp.

Trying to see other options.

Brit01 · 04:35 PM

What kind is this? 50 watts at 12V? that's 4 amps!

TRANSFORMADOR LAMPARAS ALOGEN DIMMABLE 240V AC, 12V AC - $ 80.00 - MercadoLibre

I see it is this type:

http://www.airlinktransformers.com/e...ansformers.asp

I guess this is a big NO NO as its a hf electronic tranny.

TheGimp · 24th August 2010, 06:52 PM

In reading the second link, it appears that they are switching regulators that may operate all the way down to 10KHz. I would be concerned about coupling noise into the amp, but if they are operating up at 100KHz it might not be as much of an issue.

Brit01 · 24th August 2010, 07:12 PM

They are for sale for just 4 USD!!!

Worth a try. Less than a Burgerking meal!

TheGimp · 24th August 2010, 07:23 PM

At that price I'd grab a couple. look at the output with a scope to see what the frequency is. If they are up in the 100KHz range it should be fine, you can always rectify it and regulate it with a 3-Terminal regulator to filter the noise.

Brit01 · 24th August 2010, 10:08 PM

Also just found a sale for 5 trannies , 28 v 3 amps each, for 35 USD all 5!

This could heat 4 x 6080 tubes in series with a little left over. I imagine I'll lose a little headroom.

Brit01 · 25th August 2010, 03:17 AM

Would I be able to modify one of these to reduce it to 12 or 6 volts by unwinding?
Would it still maintain it's 3 amp rating?

Or is it easier to reduce 28v to 12 volts through a series of high wattage resistors or recitify and filter?

TheGimp · 25th August 2010, 03:45 AM

If you are driving more than one tube, put them in series. Four 6.3V tubes will work on 28V with a small series resistor to drop the remaining voltage.

Or use a NTC thermistor to help hold down the inrush current and drop the remaining voltage.

24th August 2010, 03:57 PM	#1
Brit01 diyAudio Member Join Date: Jul 2008	Transformer question - 110 v and 25 v from 1 secondary? Thinking about providing 2 supplies from 1 tranny. I can get a step down tranny 220/110 with 1000 watts supply. Could I run ~120 volts 300mA and also a 25V 3.5 Amp from this 1 amp? If I calculate correctly: 1000/110= 9 Amps available How would I drop 110/120 volts to 25V to supply 3 amps from this tranny? I use PSUII to do simple circuits but never attempted to take off a tap at a much lower voltage with much higher current.

24th August 2010, 04:29 PM	#4
Brit01 diyAudio Member Join Date: Jul 2008	What kind is this? 50 watts at 12V? that's 4 amps! TRANSFORMADOR LAMPARAS ALOGEN DIMMABLE 240V AC, 12V AC - $ 80.00 - MercadoLibre I see it is this type: http://www.airlinktransformers.com/e...ansformers.asp I guess this is a big NO NO as its a hf electronic tranny. Last edited by Brit01; 24th August 2010 at 04:35 PM.

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24th August 2010, 04:03 PM	#2
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Thats a big transformer. You will get about 150-170V if you full wave rectify it. To get the 25V at 3A you have several options: (1) linear regulator = lots of power dissipation (maybe 500W continuous). (2) Switching Regulator = better efficency with the risk of noise (3) inductor input filter = lots of cost for the iron 20H 3A is a big choke! Cheaper to get the right transformer(s) to begin with.

24th August 2010, 04:25 PM	#3
Brit01 diyAudio Member Join Date: Jul 2008	Thanks Gimp. There is also a 500w version. More manageable giving about 4.5 amps. I can't get a 25v 3.5 amp tranny here. Even difficult to get a 12V more than 1 amp. Trying to see other options.

24th August 2010, 06:52 PM	#5
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	In reading the second link, it appears that they are switching regulators that may operate all the way down to 10KHz. I would be concerned about coupling noise into the amp, but if they are operating up at 100KHz it might not be as much of an issue.

24th August 2010, 07:12 PM	#6
Brit01 diyAudio Member Join Date: Jul 2008	They are for sale for just 4 USD!!! Worth a try. Less than a Burgerking meal!

24th August 2010, 07:23 PM	#7
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	At that price I'd grab a couple. look at the output with a scope to see what the frequency is. If they are up in the 100KHz range it should be fine, you can always rectify it and regulate it with a 3-Terminal regulator to filter the noise.

24th August 2010, 10:08 PM	#8
Brit01 diyAudio Member Join Date: Jul 2008	Also just found a sale for 5 trannies , 28 v 3 amps each, for 35 USD all 5! This could heat 4 x 6080 tubes in series with a little left over. I imagine I'll lose a little headroom.

25th August 2010, 03:17 AM	#9
Brit01 diyAudio Member Join Date: Jul 2008	Would I be able to modify one of these to reduce it to 12 or 6 volts by unwinding? Would it still maintain it's 3 amp rating? Or is it easier to reduce 28v to 12 volts through a series of high wattage resistors or recitify and filter?

25th August 2010, 03:45 AM	#10
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	If you are driving more than one tube, put them in series. Four 6.3V tubes will work on 28V with a small series resistor to drop the remaining voltage. Or use a NTC thermistor to help hold down the inrush current and drop the remaining voltage.

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