Home Made Variac?

Cam · May 6th, 2006, 11:55 AM

Is there such a possibility?

denny · May 6th, 2006, 01:34 PM

You can get a 1000VA chinese unit with a voltage meter and isolated secondary for under $150 - MUCH cheaper and more convenient than a house fire or a funeral.

denny

BTW, why a Variac? There may be other ways to accomplish what you want to do.

Cam · May 6th, 2006, 02:49 PM

in terms of juiceing up your own cap jobs if one ever got around to doing their own caps. Of course if one was headed in that direction, they would get the correct tools in the first place after learning all important safety and steps related..

denny · May 6th, 2006, 03:57 PM

If you are using new electrolytic capacitors, you can just install them and fire up the amp. Think of the millions of devices manufactured with caps that, in most cases, never have a voltage applied until they are powered up the first time. The forming procedure MAY be a good precaution if you are using caps that have not been used for 10-15 years. You can use batteries and a resistor if you think the forming may be necessary.

I have built well over a hundred electronic projects, kits and my own designs, and have done a good bit of circuit troubleshooting on all types of devices - audio, computer, ham radio, guitar amps, etc. The only new cap failures I can recall were caused by installing it backwards or accidentally applying a voltage WAY over the cap's rating.

I would never attempt to build a Variac-type device myself. Just too dangerous, and there are units available at a reasonable cost.

denny

Cam · May 6th, 2006, 04:13 PM

so new old stock caps would be an issue but new ones probably not? So much of what I have read says to slowly form caps.

Wally · May 6th, 2006, 06:33 PM

Cam, NOS caps are no better than old used caps. Electrolytics go bad with time whether they are in a circuit or sitting on a shelf. I never use a Variac with new caps, either. I do hook up to a current limiter. after installing caps. The limiter will indicate shorts immediately.
I have read of some people using heat to treat caps that have sat on the shelf. I've never bothered with that either, but if I had to try some NOS, I probably would be baking them in an oven just in case it would help.

Bluesbob · May 7th, 2006, 10:11 AM

a 100 watt light bulb in series.

Cam · May 7th, 2006, 02:21 PM

Bluesbob can you please elaborate on the 100 watt bulb concept?
Thanks

Bluesbob · May 7th, 2006, 09:03 PM

I don't think this is the right way to form caps and I take no responsibility for anything that might go wrong, but here's the idea. You get a light bulb socket with 2 wires attatched to it (probably in your local hardware store). You attach those 2 wires to the positive leg of an ordinary extension cord. Just cut the one (hot) wire, not both. Then screw in a 100 watt light bulb. This puts the filament in series with the power coming out of the wall. The idea is for the light bulb to soak up the initial jolt of current that goes into your amp when you first turn it on. When the light reaches full brightness, the amp is ready to run. Of course, you still have to let it warm up before taking it off standby. It works OK with older amps that haven't been used in a few years, sort of a gentle turn-on. (hey!) I don't recommend it as a substitute for a variac when forming caps.

NTC · May 8th, 2006, 06:58 PM

Quote:

Originally Posted by Bluesbob

I don't think this is the right way to form caps and I take no responsibility for anything that might go wrong, but here's the idea. You get a light bulb socket with 2 wires attatched to it (probably in your local hardware store). You attach those 2 wires to the positive leg of an ordinary extension cord. Just cut the one (hot) wire, not both. Then screw in a 100 watt light bulb. This puts the filament in series with the power coming out of the wall. The idea is for the light bulb to soak up the initial jolt of current that goes into your amp when you first turn it on. When the light reaches full brightness, the amp is ready to run. Of course, you still have to let it warm up before taking it off standby. It works OK with older amps that haven't been used in a few years, sort of a gentle turn-on. (hey!) I don't recommend it as a substitute for a variac when forming caps.

If the light reaches full brightness, there is a SHORT in the amp. A lightbulb has a very low resistance when it is cold - that is, off. That is why hooking it in series with the amplifier even works. The bulb will need 120V across it to get to full brightness. If you have an amp in series with it, the brightness should never get to full - you will have some voltage across the amp. Ideally, the bulb would NEVER light and you could run the amplifier. I have a setup like this, but I never actually play the amp with it hooked to the lightbulb. I only use it a first-time turn-on test to make sure there aren't any shorts. Gerald Weber's first book describes the making of one of these contraptions....

May 6th, 2006, 11:55 AM	#1 (permalink)
Cam Tele-Afflicted Join Date: Mar 2003 Location: Snow Piles Alberta Canada Posts: 1,020 7 Photos	Home Made Variac? Is there such a possibility? __________________ Relic Schmelic! Play the darn thing! Wipe it down after and put it in it's case!

May 6th, 2006, 01:34 PM	#2 (permalink)
denny Tele-Meister Join Date: Jan 2004 Location: North of Dallas Posts: 454	NO You can get a 1000VA chinese unit with a voltage meter and isolated secondary for under $150 - MUCH cheaper and more convenient than a house fire or a funeral. denny BTW, why a Variac? There may be other ways to accomplish what you want to do.

May 6th, 2006, 02:49 PM	#3 (permalink)
Cam Tele-Afflicted Join Date: Mar 2003 Location: Snow Piles Alberta Canada Posts: 1,020 7 Photos	Denny, I guess I was thinking.... in terms of juiceing up your own cap jobs if one ever got around to doing their own caps. Of course if one was headed in that direction, they would get the correct tools in the first place after learning all important safety and steps related.. __________________ Relic Schmelic! Play the darn thing! Wipe it down after and put it in it's case!

May 6th, 2006, 03:57 PM	#4 (permalink)
denny Tele-Meister Join Date: Jan 2004 Location: North of Dallas Posts: 454	Forming Caps If you are using new electrolytic capacitors, you can just install them and fire up the amp. Think of the millions of devices manufactured with caps that, in most cases, never have a voltage applied until they are powered up the first time. The forming procedure MAY be a good precaution if you are using caps that have not been used for 10-15 years. You can use batteries and a resistor if you think the forming may be necessary. I have built well over a hundred electronic projects, kits and my own designs, and have done a good bit of circuit troubleshooting on all types of devices - audio, computer, ham radio, guitar amps, etc. The only new cap failures I can recall were caused by installing it backwards or accidentally applying a voltage WAY over the cap's rating. I would never attempt to build a Variac-type device myself. Just too dangerous, and there are units available at a reasonable cost. denny

May 6th, 2006, 04:13 PM	#5 (permalink)
Cam Tele-Afflicted Join Date: Mar 2003 Location: Snow Piles Alberta Canada Posts: 1,020 7 Photos	Thanks Denny...and so new old stock caps would be an issue but new ones probably not? So much of what I have read says to slowly form caps. __________________ Relic Schmelic! Play the darn thing! Wipe it down after and put it in it's case!

May 6th, 2006, 06:33 PM	#6 (permalink)
Wally Friend of Leo's Join Date: Mar 2003 Location: Lubbock, TX Posts: 4,212	Cam, NOS caps are no better than old used caps. Electrolytics go bad with time whether they are in a circuit or sitting on a shelf. I never use a Variac with new caps, either. I do hook up to a current limiter. after installing caps. The limiter will indicate shorts immediately. I have read of some people using heat to treat caps that have sat on the shelf. I've never bothered with that either, but if I had to try some NOS, I probably would be baking them in an oven just in case it would help.

May 7th, 2006, 10:11 AM	#7 (permalink)
Bluesbob Tele-Afflicted Join Date: Mar 2003 Location: East Suffolk L.I. Posts: 1,073 20 Photos	Try... a 100 watt light bulb in series. __________________ What, me worry?

May 7th, 2006, 02:21 PM	#8 (permalink)
Cam Tele-Afflicted Join Date: Mar 2003 Location: Snow Piles Alberta Canada Posts: 1,020 7 Photos	??Bluesbob Bluesbob can you please elaborate on the 100 watt bulb concept? Thanks __________________ Relic Schmelic! Play the darn thing! Wipe it down after and put it in it's case!

May 7th, 2006, 09:03 PM	#9 (permalink)
Bluesbob Tele-Afflicted Join Date: Mar 2003 Location: East Suffolk L.I. Posts: 1,073 20 Photos	Sure... I don't think this is the right way to form caps and I take no responsibility for anything that might go wrong, but here's the idea. You get a light bulb socket with 2 wires attatched to it (probably in your local hardware store). You attach those 2 wires to the positive leg of an ordinary extension cord. Just cut the one (hot) wire, not both. Then screw in a 100 watt light bulb. This puts the filament in series with the power coming out of the wall. The idea is for the light bulb to soak up the initial jolt of current that goes into your amp when you first turn it on. When the light reaches full brightness, the amp is ready to run. Of course, you still have to let it warm up before taking it off standby. It works OK with older amps that haven't been used in a few years, sort of a gentle turn-on. (hey!) I don't recommend it as a substitute for a variac when forming caps. __________________ What, me worry?