Variac?

[Scribble]

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]

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]

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]

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]

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

 

[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.

 

[Sandy H.]

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]

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!
😀

 

[D3]

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]

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

 

[dnsey]

Find a couple of multi-tapped mains transformers and connect them back-to-back with provision for switching between windings.
Doesn't matter what the secondary voltages actually are as long as they are similar ranges, and the overall rating of the txs is adequate for what you want to power plus a bit for losses.

eg - HT in > 6V sec >12V sec > approx 0.5 HT out:

HT 6V 12V 0.5HT
---II------.------II---
---II------.------II---

 

[dnsey]

Well, the formatting changed a bit between the preview screen and my published post, but I hope you get the idea!

 

[D3]

VARIAC

Hi Cr3ator..........
Yup got mine on ebay....for £65..........it's an 8amp jobby.........
once I've used it I will selll it on....................cheap deal really...
should get money back!

I recommend that all you guys do this...............

D3 Bolton uk

 

[Frazzled]

I purchased a 20A variac new for US$110 and there is no way I will be selling it, it is just way too useful!

 

[D3]

Variac

Hi Fraz.............
Thats a great deal........you've had........could you post where you got it............or a link.....I think the guys on this site would find it usefull.


Richard Bolton Uk

 

[anatech]

For small projects & "normal" amplifiers, a 2 amp variac is fine. I use that most of the time and go to the 10A model for big tube amps .... or one of Nelson's designs.
Very useful device.
-Chris

 

[Variac]

Variacs are very good things. They are clever in design, and come in a multitude of forms and shapes. They had been around a long time so there are vintage models too. One should start a collection immedietly. I have one as a doorstop and one to dim my tracklights, and a couple for makin' amps... You can adjust the output of your Son o Zen to just a cople of watts when you just need background music...Plus the name is super-cool 😎

As they say about oil wells in Texas: "If you ain't got one-get one"