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Old 24th January 2003, 02:34 PM   #1
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Exclamation Variac?

Ive read that it is essential to use a variac and slowly up the voltage the first time you run the amp and measure some points some where?

I understand the measuring part but is a variac absolutly necessary. As they are rather pricey (AU$199) i would not be willing to buy one. Is there another safe avenue i could take?

I was unshore wether this belogns here or in the electroncis forum. Moderators move at will

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Joel
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Old 24th January 2003, 02:44 PM   #2
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If you have done everything right there is no need for a variac but it's nice to it just in case. The use of a variac is just protection against blue smoke but one another trick is to fuse down the amp. Use a little bit smaller fuses.
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Old 24th January 2003, 02:47 PM   #3
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Ive read bout that too. Thast where you start off with low value fuses then go up a little untill they dont blow any more on normal operation?

Please correct me if i wrong as im here to learn

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Joel
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Old 24th January 2003, 02:56 PM   #4
tiroth is offline tiroth  United States
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Put a light bulb in series with your transformer primary. Check www.sound.au.com or in the forum logs for more info about this.
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Old 24th January 2003, 02:58 PM   #5
Electrons are yellow and more is better!
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Try to calculate how much the amp will draw with a low signal (output power). Don't use too small fuses.
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Old 24th January 2003, 04:49 PM   #6
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Anybody who is serious about this will want to buy
wire cutters, soldering iron, multimeter, scope,
and a Variac (tm) in that order. An oscillator you can
build once you have a scope.
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Old 27th January 2003, 02:15 PM   #7
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Default I was close. . .

I have the cutters, iron, multi-meter, scope and decided to build a +/-25V adjustable lab supply (Rod Elliot project). Guess I should have gone with the variac. . .

A quick question, though: I can use the adjustable supply to re-form older caps? It seems that if I were to throw in a 10k resistor and connect my PS caps one at a time to the supply, I could bring the voltage up from 1-25V and drain back down with a resistor. Is that the proper technique?

Considering the above, I plan on being quite cautious with the caps, as is always recommended.

Any other suggestions for re-forming or testing surplus caps?

S.
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Old 26th July 2004, 10:32 PM   #8
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Quote:
Originally posted by Nelson Pass
Anybody who is serious about this will want to buy
wire cutters, soldering iron, multimeter, scope,
and a Variac (tm) in that order. An oscillator you can
build once you have a scope.

Check, check, check, check and check!
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Old 28th July 2004, 07:58 AM   #9
D3 is offline D3  England
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Default Testing 1-2-3..phuttttt

Frazz is right.................on the last project I did...it took me ages to check things out........only to be caught out with a tiny solder...... track....(about width of a human hair).......this gave me a real fright..........when a mini cloud of smoke rapidly appeared.

Fortunately no damage ensued......but this was a low power preamp.........I think the china syndrome is far more likely with a powerfull poweramp........and big powersupplies......any body fancy a bacon sandwich....

So .... I've invested in a variac........you just can't be too carefull.

D3 Bolton uk
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Old 28th July 2004, 12:37 PM   #10
Cr3ator is offline Cr3ator  Netherlands
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Default Ebay

There are plenty of Variacs for sale on Ebay or other websites where you can buy second hand stuff. You can find them from $2 - $600... good luck!

ErikH
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