Mr. Wizard, what's a variac?
- Thread starter djronc
- Start date
Register to hide this ad
It's a piece of equipment that allows you to start up a piece by slowly raising the voltage, rather than just plugging it in at 120 volt.
Can start at 0 and go up as you wish. Has variable voltage settings.
Other things can be done too, but this is a basic use for testing stereo equipment.
I've used mine for bench testing car radios at 12 volt for example. Older ones at 6 volt.
Can start at 0 and go up as you wish. Has variable voltage settings.
Other things can be done too, but this is a basic use for testing stereo equipment.
I've used mine for bench testing car radios at 12 volt for example. Older ones at 6 volt.
Thatch_Ear
Addicted Member
It is a Variable AC transformer and is used to warm capacitors up especially if they have been dormant a long time. This can keep the caps from being ruined and in the case of the large filter electrolitics in the power supply from getting a 60 cycle hum.
variac and electrolytics.
Thatch,
The way you worded your statement could lead to disaster. Yes, variacs are ideal for re-forming electrolytic caps....as long as the variac is used to power the receiver or amp the caps are in, and not connecting to electrolytic caps directly. AC on electrolytics will break down the dielectric and cause them to fail or explode violently. By applying about 50 volts line voltage to a vintage piece of electronics with a tube rectiifier, the rectifier tube gets just enough filament voltage to make a bit of DC at reduced voltage before the rest of the tubes are sufficiently heated to draw off this power. This places a lower than normal voltage on the electrolytics in the B+ and re-forms the oxide dielectric coating in the capacitors, refurbishing them. Electronics, even tube amps with SS rectifiers get DC right off the bat just above zero on the variac as the recitifiers come on as soon as there is any voltage at all (above their usual 0.7 volt drop). A big Marantz SS amp for example could have its capacitors re-formed by starting say at 10 volts and slowly working up to full line voltage in 10 volt increments every hour over a day or so.
It is a good idea to wire a household 60 watt or 100 watt incandescent light bulb in series with the set being reformed and the variac to limit the current in case the vintage electronics has a fault. This will save the power transformer or other components, and is a good indicator of what's going on.
Rob
Thatch,
The way you worded your statement could lead to disaster. Yes, variacs are ideal for re-forming electrolytic caps....as long as the variac is used to power the receiver or amp the caps are in, and not connecting to electrolytic caps directly. AC on electrolytics will break down the dielectric and cause them to fail or explode violently. By applying about 50 volts line voltage to a vintage piece of electronics with a tube rectiifier, the rectifier tube gets just enough filament voltage to make a bit of DC at reduced voltage before the rest of the tubes are sufficiently heated to draw off this power. This places a lower than normal voltage on the electrolytics in the B+ and re-forms the oxide dielectric coating in the capacitors, refurbishing them. Electronics, even tube amps with SS rectifiers get DC right off the bat just above zero on the variac as the recitifiers come on as soon as there is any voltage at all (above their usual 0.7 volt drop). A big Marantz SS amp for example could have its capacitors re-formed by starting say at 10 volts and slowly working up to full line voltage in 10 volt increments every hour over a day or so.
It is a good idea to wire a household 60 watt or 100 watt incandescent light bulb in series with the set being reformed and the variac to limit the current in case the vintage electronics has a fault. This will save the power transformer or other components, and is a good indicator of what's going on.
Rob
Last edited:
Thatch_Ear
Addicted Member
Rob,
Since Variacs tend to come equipped with an AC plug for what ever it is you are going to warm up I seriously doubt that anyone would try to hook it directly up to a capasitor.
And as anyone that pulls the bottom off a tube amp for the first time would not, if they had more than 2 live brain cells, try to pick out anything they might attach a variac to. That is if they could find anything other than the power cord that might plug into a Variac.
I also in case you didn't notice brought up the vintage tube care thread where I went through how to use a variac on tube gear step by step.
I might have been a bit vague about how to actually use one but that is why I brought the thread that explains how to do this and planted it right next to where this one was at the time.
Also being a vague as I was I doubt anyone would have started pulling capacitors out of gear and cranking the variac to the limit and blow the thing up. They would have asked questions or just ignored us and plugged the gear in anyway.
Confusion,yes. Disaster? I doubt it. Not unless they are already a candidate for the Darwin Awards.
Since Variacs tend to come equipped with an AC plug for what ever it is you are going to warm up I seriously doubt that anyone would try to hook it directly up to a capasitor.
And as anyone that pulls the bottom off a tube amp for the first time would not, if they had more than 2 live brain cells, try to pick out anything they might attach a variac to. That is if they could find anything other than the power cord that might plug into a Variac.
I also in case you didn't notice brought up the vintage tube care thread where I went through how to use a variac on tube gear step by step.
I might have been a bit vague about how to actually use one but that is why I brought the thread that explains how to do this and planted it right next to where this one was at the time.
Also being a vague as I was I doubt anyone would have started pulling capacitors out of gear and cranking the variac to the limit and blow the thing up. They would have asked questions or just ignored us and plugged the gear in anyway.
Confusion,yes. Disaster? I doubt it. Not unless they are already a candidate for the Darwin Awards.
