Do I need a VARIAC?

[Winetree]

I've been building a lot of projects.
Upon completion, my usual practice is to make the sign of the cross and flip the switch.
Should I be using a VARIAC to bring up the power slowly?

 

[shabtek]

there is the series light bulb thing to limit current/let you know there is a short.

 

[mjrippe]

Using a Variac is only going to help you if you have some sort of current monitoring as well.  Some variacs have ammeters built in so you can see the current draw as you raise the voltage, or you can make a box with test points.  Otherwise you're still turning it on blind.

 

[CJ]

if the fuse is sized right....jus sayin...

if the fuse blows, just jumper across and plug in for a smoke test, quickest way to find the backwards cap jus kidin,  ;D

 

[PRR]

> building a lot of projects. ... sign of the cross and flip the switch

I hang a chicken (makes a good snack afterward); but new parts correctly wired do NOT need gradual start-up.

You should have line-fuse. For your mistakes, for the rare bad part, and for long-term.

If there is doubt about the workmanship, _or_ if a repair-job won't hold a fuse, a lamp limiter is very wise.

 

[Winetree]

I've built over 100 projects and only popped one backwards cap.
I guess my real concern was the inital blast of power to new parts,
but than a blast  happens every time you turn them on.
Responses suggest I don't need a Variac.
I still have first time fears.
Thanks

 

[Mike Cleaver]

If you work with a lot of old tube equipment, a variac is good to have.
Capacitors that have been sitting idle in the power supply sometimes can be saved with a slow re-awakening.
Plugging in an old mothballed piece of tube gear without carefully checking it visually and electronically can be a recipe for disaster, frying irreplaceable transformers, etc.
If a piece of gear is over 30 years old, the power supply caps almost certainly will need replacement but sometimes, you get lucky.
The other part that must be replaced, selenium rectifiers.
These release deadly gasses when they fail.
Replace them with modern diodes but check to make certain you are getting the proper voltage required by the schematic.

 

[JohnRoberts]

I have a variac that I found handy for working on power amps, but it is worth noting that some circuits do not bias up and work properly unless at correct voltage. I rarely use it for non-power circuits.

If you have the option (and concern)  perhaps leave expensive IC off the build until you have confirmed that power supply comes up and is providing correct voltages.

Most drama and excitement comes from PS mistakes in non-power amps. Power amps can draw huge current from output stages both trying to be on at the same time.

JR

 

[mjrippe]

John is correct, some power amps (solid state) will FREAK OUT if you try to variac them.  But most of the DIY here does not seem to be power amps.

In both tube and solid state it can be helpful to remove the tubes/ICs/etc. from the audio portion and test the PSU first.

And YES, fuses are a must but having an ammeter in line will save you from buying lots of fuses ;-)

 

[gar381]

http://www.circuitspecialists.com/content/55669/tdgc2-0.5-0.jpg

Nice for firing up rebuilt power amps.

You don't need one for most things but at $51 you should have one handy.

Best

GARY