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Old 3rd January 2006, 01:16 AM   #1
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Default Unknown mA on Gardners mains transformer

Hi Everyone!,

I have obtained a Gardners power transformer with the following specs but without any mA rating from top to bottom:

Gardners "RS-3134"

Prim:
10-0-200-220-240 and an "SCR" tap?

Secondaires:
0-5-6.3 ~ 2A = 12.6 watts
6.3v-0 ~ 3A = 18.9 watts
6.3v-0 ~ 1A = 6.3 watts

350-300-0-300-350 ~ NO mA rating..

It looks the exact dimensions as this: http://www.diyaudio.com/forums/attac...amp=1120792609

It weighs about 5 kg at least..

I've tried taking one of the endcaps off, no luck I need a special tool to remove the poles going to the other side so I can't gauge the size of the turns, maybe I can determine the amount of current I can draw by building a series-wired light bulb circuit and watching for voltage drop?

Any guidelines on how to determine what a transformer can supply? my last resort is to take it to my uncle and see if he can figure it out via reading ohmage...

I would like to use this transformer on the KT88 SE project by Mikael Abdellah..

Cheers!
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Old 3rd January 2006, 01:50 PM   #2
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Location: Paris - France
Layberinthius,

There are two threads with informations on the: RS 3134

http://www.diyaudio.com/forums/showt...36410-p-4.html
http://www.diyaudio.com/forums/showt...?postid=535721

Gardners Model # RS 3134
Specs are: 350-300-0-300-350 .. 200mA = 70w

If that information can help.

Regards.

Alain.
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Old 3rd January 2006, 05:58 PM   #3
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Location: Alps:Tube amp designs over 150W, SMPS guru.
I've got the Solent series cat in front of me...RE3134
No Not 200mA
It actually shows
prim 10-0-200-220-240
sec 350-300-0-300-350 100mA (their size 40/S40; weight 8Lbs)
0-5-6.3V 2A
6.3V 3A
6.3V 1A

These trannies were pretty well made under near military spec. I wouldn't fiddle with trying to bend it about.

Hope this helps
richj
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Old 4th January 2006, 12:45 AM   #4
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I'll try and measure this RS-3134 today with a baby weight scale, if it comes to 8lbs I'll assume it's 100mA, if it's any heavier, I'll assume a higher rating...
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Old 4th January 2006, 01:03 AM   #5
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Quote:
Originally posted by richwalters
I've got the Solent series cat in front of me...RE3134
No Not 200mA
It actually shows
prim 10-0-200-220-240
sec 350-300-0-300-350 100mA (their size 40/S40; weight 8Lbs)
0-5-6.3V 2A
6.3V 3A
6.3V 1A

These trannies were pretty well made under near military spec. I wouldn't fiddle with trying to bend it about.

Hope this helps
richj

Congratulations!, it's 7 lb 7 ounces....

Damn....

Oh well, it'll come into good use for another project definatley =)

Thank you heaps richwalters!

Btw, I did post a photo of this transformer and it's /assumed/ specifications about a year back, I shouldn't have assumed it's current rating then but I do know now..

For the record, I think I can safely state now that a Gardners RS-3134 has a 100mA rating on the 350-300-0-300-350 taps...
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Old 4th January 2006, 09:33 PM   #6
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As a general help to determine allowable current, I have found that most small tube power transformers are designed for copper loss of about 4%. (Small being up to say 300W.)

Thus, if the d.c. winding resistance is measured and one takes 4% of the rated r.m.s. voltage, Ohms Law will give a current not too far away from the designed value.

E.g. a 350-0-350 Vac secondary gave an average resistance of 170 ohm per half. Taking a 4% voltage drop gives 14V. Divide by 170 ohm gives 82 mA. (It was rated for 80 mA.)

This method will be a little difficult for low voltage windings because of difficulty in determining resistance accurately, but works well for high voltage windings when all else failed. (Total copper loss for the transformer will of course be higher because there is also loss in the primary; I am looking at the secondary only.)
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Old 19th January 2006, 12:04 PM   #7
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Quote:
Originally posted by Johan Potgieter
As a general help to determine allowable current, I have found that most small tube power transformers are designed for copper loss of about 4%. (Small being up to say 300W.)

Thus, if the d.c. winding resistance is measured and one takes 4% of the rated r.m.s. voltage, Ohms Law will give a current not too far away from the designed value.

E.g. a 350-0-350 Vac secondary gave an average resistance of 170 ohm per half. Taking a 4% voltage drop gives 14V. Divide by 170 ohm gives 82 mA. (It was rated for 80 mA.)

This method will be a little difficult for low voltage windings because of difficulty in determining resistance accurately, but works well for high voltage windings when all else failed. (Total copper loss for the transformer will of course be higher because there is also loss in the primary; I am looking at the secondary only.)
That'll help quite a bit in the marking of previously unmarked trafos, thanks!
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