I have no idea how the Variac does what it does, and now that it isn't doing what it should I'm even more baffled.

I use the Variac to control the fan which pulls the air though the HUKY. Simple.
Except that the Variac misbehaves.
Periodically I notice that the fan is simply not turning at all even though the V is set up fairly high.
I'm not sure yet, but it may be that it fails only when I am turning it down - say from 78 to 56 - .
In any case (duh, check the smoke) I frequently discover that the fan is simply sitting there not turning at all....
Very annoying.

Is there a protocol for figuring out what is going wrong and trying to fix it?
Or is this now a door stop?

A variac regulates the voltage and can step up or down. For example, I use a variac on my tube amp to reduce the line voltage from a fluctuating +/- 120v to a constant 115v.

That part I understand, but thank you.
How it does it is what I mean I don't understand....and probably don't really need to.

Why it has these apparent deadspots is what is curious to me.

A variac is basically a variable transformer. It varies the voltage by changing the ratio of primary windings to secondary windings. This is usually done with a carbon wiper arm that moves across one set of windings changing the ratio by including more or less of the windings. You move this wiper arm when you turn the dial to change the voltage output. If there is a dead or dirty spot on the coil contact area of the wiper arm it will affect the voltage. You could try moving the wiper arm back and forth through its range quickly. Sometimes that will clean the points of contact. Or you can take it apart and clean the coil and wiper arm with compressed air or electrical contact cleaning spray.

SJM wrote:Why it has these apparent deadspots is what is curious to me.

The wiper arm is a mechanical connection gliding over copper wire (winding) and, as such, dirt can accumulate between the windings and eventually build up to cause dead spots. Here's one with the cover removed to you can see the wiper arm (top plate) and the windings

Source: https://en.wikipedia.org/wiki/Autotrans ... mer_01.jpg

Contact cleaner will get rid of the deadspots.

What type of dirt is on the windings in the photo above? I vacuum mine out occasionally, but I've never had the cover off mine. Also with a voltmeter, you could check to see how the output voltage varies as you rotate the dial. Next thing I would inspect is the motor to see if it's gunked up with coffee debris.

Excellent. Thank you.
I will take her apart.
Now one more question. Do I start with the bolt configuration on the bottom or the two phillips screws on the front and back?

I think that unit isn't a Variac(TM) brand - I don't see that part number at http://www.variac.com (and thus, no drawings, etc.)

My guess - guess - is to start with the phillips screws. I wouldn't undo the bolt, I am guessing that would be the main axle. You might have to get the knob off as I would guess there are more screws under the knob.

However, as mentioned by LDT above, first test with a voltmeter, then confirm that it isn't the fan motor that is the issue, and then look at taking the cover off of the autotransformer.

I'll let you know how I do. Thanks for giving me some direction.

So this morning I plugged the Kill A Watt into the pseudo-Variac, and here's what I got



So, what would you recommend next?
Obviously I'm totally missing the bottom range ....Hmmmph.