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Scribble 24th January 2003 02:34 PM

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 :)

Thanks,
Joel

peranders 24th January 2003 02:44 PM

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.

Scribble 24th January 2003 02:47 PM

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 :)

Thanks
Joel

tiroth 24th January 2003 02:56 PM

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.

peranders 24th January 2003 02:58 PM

Try to calculate how much the amp will draw with a low signal (output power). Don't use too small fuses.

Nelson Pass 24th January 2003 04:49 PM

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.

Sandy H. 27th January 2003 02:15 PM

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.

Frazzled 26th July 2004 10:32 PM

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!
:D

D3 28th July 2004 07:58 AM

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

Cr3ator 28th July 2004 12:37 PM

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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