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Old 18th February 2009, 01:44 PM   #2991
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by AndrewT
Hi,
add a bank of 10r 5W resistors together for a soft start ballast.

I use between 30r and 60r for my transformers.
A pair of series 5r0 thermistors will not look like much to a 240Vac supply.

Without a soft start you may need a T8A fuse to start the transformer reliably, i.e. without nuisance blowing every month or two.

Hi,

Would there be any risks to the amplifiers circuity or transformer by using no soft start, becuase of the large inrush?

R
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Old 18th February 2009, 01:54 PM   #2992
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Your caps aren't fully formed yet so they look like a dead short to the trans. Wire up a lightbulb in series as a current limiter and let it cook for a couple hrs then try it.

Best, Bill
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Old 18th February 2009, 01:55 PM   #2993
rhysh is offline rhysh  United Kingdom
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A standard 60W filament bulb?
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Old 18th February 2009, 02:01 PM   #2994
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Anything will work. When you turn it on the light will burn brightly for a second or two, then it will dim. Just let it run like that for a while and your caps will form. If the bulb doesn't dim then there problems somewhere. I start everything I build this way, Poor Man's Variac.

Bill
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Old 18th February 2009, 02:03 PM   #2995
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by rhysh
Thermistor is going to be a month! Does anyone have any they could sell to me?

have you any broken PC PSU around ?

you can scavenge NTC that way ......
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Old 18th February 2009, 02:06 PM   #2996
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Quote:
Originally posted by Zen Mod



have you any broken PC PSU around ?

you can scavenge NTC that way ......

I have loads of PC PSU's. Where abouts would i find the thermistor? Near the mains inlet?
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Old 18th February 2009, 02:07 PM   #2997
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by Bill Fuss
Anything will work. When you turn it on the light will burn brightly for a second or two, then it will dim. Just let it run like that for a while and your caps will form. If the bulb doesn't dim then there problems somewhere. I start everything I build this way, Poor Man's Variac.

Bill

Sounds good. Would i still need a 8A fuse whilst doing this, or should i use the standard 1.25A?
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Old 18th February 2009, 02:16 PM   #2998
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A 60W bulb will limit the current to about 1/4A so the 1.25 fuse is fine. In the end a 2A slow blow with a CL60 would probably be my choice.

Best, Bill
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Old 18th February 2009, 02:18 PM   #2999
rhysh is offline rhysh  United Kingdom
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Quote:
Originally posted by Bill Fuss
A 60W bulb will limit the current to about 1/4A so the 1.25 fuse is fine. In the end a 2A slow blow with a CL60 would probably be my choice.

Best, Bill

Thanks, im just creating this contraption now.
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Old 18th February 2009, 02:33 PM   #3000
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Quote:
Originally posted by rhysh
I have just powered up my f5, just the PS. I am using 1.25A fuses on 230v mains. I have tried three times and the fuse blows every time.

Could this be the inrush current of the transformer? The fuse will blow when the transformer alone is connected.

A variac would help in this situation. If you turn the voltage up slowly, and the
variac vibrates unusually, or your fuse blows, you know you have a problem
(hopefully before anything else is destroyed). I got a new 500VA one at Fry's
(in the USA) for about $70 (if I remember correctly).

Good luck,
Robert
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