[ARC5] Slightly OT: Transformers

[Dennis Monticelli]

If you have an audio signal generator, use it to drive what you think is
the primary with several volts and then just put a meter on the other
leads.  If you have an old-fashioned capacitor checker (like a Heathkit or
Sprague), many of those will utilize the built-in bridge to measure turns
ratios directly without applying power.

Both of these techniques are completely safe.

I would like to add that sometimes moisture has crept into the old
transformer and that is just a problem waiting to happen.  You can measure
isolation resistance with a megger.  The cap checkers I mentioned can apply
several hundred volts and measure uA leakages so they could be employed as
well.  If there is suspected moisture ingress some folks have turned to a
low temp bake in the oven for several hours (when the XYL is out of the
house).  Another idea is to put enough DC current into an inner winding to
warm up the transformer from the inside for several hours.

Dennis AE6C


On Wed, Nov 27, 2013 at 3:10 PM, Eric Mynes <kc8wzb at gmail.com> wrote:

> Greetings all,
>
> I have some questions about transformers and this seems to be the only
> group I'm in now that deals with tube rigs.  I hope you don't mind elmering
> me a bit by answering a few questions.  I mention slightly off topic
> because one day (hopefully soon) I'll start building a power supply to use
> with my ARC 5 rigs, but for now, I just want to be able to power some basic
> homebrew tube transmitters.
>
> So, my questions go along the lines of...  I have several transformers that
> have followed me home from hamfests or someone has given me.  But most are
> not labeled in any fashion as to what they are rated for.  As stated above,
> I'd like to build a small power supply that can run some homebrew tube
> rigs.  I might actually use some of the thousands of tubes that followed me
> home from hamfests instead of leaving them piled in boxes with no use.
> I've tried googling any number or marking on the transformers trying to
> find a manufacturer or specifications and haven't had any luck.  How can I
> test these safely as to not hurt myself or the transformer so that I find
> out at least the voltages I should expect out of them?  Right now, I'm not
> too concerned about finding how many amps they will provide as much as now
> much voltage is on the end of the wire.  The number of amps question will
> come soon though.
>
> Currently I have a transformer on my bench that has the following markings
> 110v004h82
> 352052
>
> It appears to have 3 windings.  A black set (I presume is the primary), a
> red set with CT, and a green set with CT.
>
> I'm kind of skittish at just applying 110v to the black wires and seeing
> what the others have for voltages.  So, I figure why not ask some hams that
> might have a better clue than me.
>
> Please respond to me off the list as I don't want to waste too much of the
> list's bandwidth on something that might be determined as an elementary
> question that we all should know.  I'll be quick to say that I'm a very
> much at an elementary stage on using HV and know enough to ask questions
> before just trying things.
>
> Thank you for the bandwidth and Happy Thanksgiving to all
>
> 73,
> Eric
> k8ohz
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