Transformer testing device

FXBDM 1832

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I have a few output transformers for which I have very little information (old radio pulls). I understand that the way to go about finding the windings ratio is to measure the voltage ratio when supplying AC to one side of the windings.

Most sources I have seen online suggest using the 5v or 6.3v windings from the power transformer. Of course, this isn’t a portable solution and you need to have an unused PT lying around (I do have one, but it’s wired in to the radio and I don’t want to play around with the old leads too much, sometimes they are brittle)

I was thinking more along the lines of generating a signal from a phone app, and then amplifying this through a diy LM386 amp. Would that work? Or am I better off using the PT trick?

Also, do I need to have a load connected on both sides of the OPT?
 

old wrench

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I had a couple of "mystery" PT's that had no markings or numbers on them that I could use to research their specs.

For starters, I checked the resistance of the different windings with a regular meter - the readings actually gave me a pretty good idea of what might be what - the ratios become apparent

Then I did the same thing Intubator did - hooked up to a variac and read the voltages - started out low, then worked up to main-line voltage so I could get the actual (although un-loaded***) voltage readings

A variac has come in pretty handy for my amp building projects - variacs aren't very expensive and there isn't much that can go wrong with them - I picked up an older used one pretty cheaply - it's a giant behemoth, a 20 amp - no need to go anywhere near that big for guitar amps - a 5 amp, or maybe even a 3 amp should do

My big variac also serves as a speed control for some of my old routers - just make sure that the motor is an old-style "universal" motor - not one of the newer electronically controlled motors with "soft start", or you might end up making some smoke ;)

edit: *** In my experience, measuring the output voltages of a PT without a load will result slightly higher reading - but close enough to be relative


If you want to get a broader response to your question - post it up in the Shock Brothers part of the forum - some very sharp electrical and electronics minds over there :)

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FXBDM 1832

TDPRI Member
Joined
Jan 21, 2022
Posts
99
Age
38
Location
Québec, Canada
If you want to get a broader response to your question - post it up in the Shock Brothers part of the forum - some very sharp electrical and electronics minds over there :)

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i must admit I hesitated between here and there, but chose here since it was mostly a tool/equipment question.
 




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