Homemade Variac?

I have an old Phillips tube radio and believe I need to bring it back to life slowly.Can I make something like a Variac for this purpose?
Greg

Here's a link to the poor man's variac... enjoy!

Poor Man's Variac

There's others out there, but I found this one doing a Google search.

Scott

Thanks Scott.
Greg

I built and used one of those when bringing up my old Fisher gear. Works very well, is cheap and convenient. If you decide you no longer need it in the future, you'll have a batch of spare bulbs for use around the house.

- JP

I take it you just start out with a low watt bulb then progress on up to say 100 watter.How much time at each stage?
Greg

Hmm, it's been a while, but I believe I waited a couple of hours at each voltage step, but I used more wattage levels than recommended by that page. I did monitor the voltage with a multi-meter to track what each step ended up at as determined by the bulb voltage. Iirc, 100 watts was insufficient to near regular line voltage in as small a step as the others so I used an even larger bulb, such as, iirc, a 150 watter before the last step up to 120v.

- JP

Kool,
Thanks guys,got someplace to start now.
Greg

Why not just buy a varaic off ebay for $50 and do the job properly ??????????

Here's another vote for the "poor man's variac". I've used it to restore countless of old radios and tube amps. Works like a charm. Don't waste your money on a variac!

I second the Phil Nelson "poor man's variac" link. Very useful indeed!

Would there be any advantage/disadvantage to using a dimmer type switch for further control?

I think there is a problem in that audio equipment uses resistors. Same reason that a soldering iron station can't be used. BTW I was once corrected regarding Variac vs. Variable Transformer but if someone happens to come across a Variac I have a link to a site that shows how to build a Variable Transformer. Some knucklehead on e$ay sells it as a pdf.

Not a bad idea, actually. The dim-bulb tester can still be useful, though even if you do have a variac. My B&K combination variac-isolationtransformer thing has the dim-bulb idea built in. there is an outlet on the back for the bulb, and a switch on the front panel for direct or dim-bulb. The dim-bulb is very useful for troubleshooting power supplies that have something shorted.

When bringing something to life slowly, I find it useful to clip the multimeter accross the B+ supply of the device being brought back to life, like across one of the filter capacitors for example.

Often the reason for doing a slow start is to "re-form" the capacitors. Opinions vary whether re-forming works. I think it cant hurt to avoid shocking the filter capacitors, so I bring them up slow.

I mention this because the voltage across the filters does not really follow line voltage as you bring it up. An awful lot of the action is between 50-60 volts. By monitoring the B+ voltage, you can see what is really happening.

YMMV

John

Here is the link to to build your own. I'm sure you could cut out the bulb circuit if you wanted. I picked up a 5 amp transformer but haven't got around to build the autotransformer yet as I was later gifted one.
http://www.vacuum-tube-power-supply.com/