[ARC5] Slightly OT: Transformers

[Ian Wilson]

Hi Eric,

I think these are excellent questions and I hope that those with
knowledge to share will respond *on* rather than *off* list.

Here is a very useful link that has, among other things, a copy
of the type of service that you can get from a transformer with
a given weight:
http://wb0nni.dakotamade.com/xfmrpwr.html

My practice with an unknown transformer is to make an intelligent (ha!)
guess what the windings are, then apply a fraction of 110V (e.g. 11V)
to what I think is the input winding, and measure the various outputs.
Take considerable caution when doing this since there can easily be
hundreds of volts present if you guessed badly. But often you can tell
what is what from the current-carrying capacity of the various wires.
Also, the resistances will tell you a lot:
  - AC input somewhere in the 5-20 ohm range
  - high-current heaters in the fractional ohm range
  - HV windings in the 100-300 ohm range (and look for centre-
    tapped windings by their 1:2 DC resistances)
All these are very approximate.

73, ian K3IMW



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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