Found a transformer at a thrift store and am curious...

[EasyGoing1]

I don't know a whole lot about transformers beyond what they do functionally ... I've never made a circuit that incorporated a transformer so I've never had to spec one out or even figure out how they connect. The one time I tried to re-use a transformer from a circuit I connected it wrong and literally made a loud bang when I connected power to it ...

Anyways, I found this one at a thrift store for $1.25 and was wondering if it could be used to step down 120V AC ... it looks like it was used somehow in an audio circuit as each side has what looks like a Common pin then a selection of wattage and on the other side, a choice of 4, 8, or 16 Ohms, which I assume is relevant to the speaker you're connecting it to...

Why would a transformer be used in audio in the first place?

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

If you're younger than around 50 years or so, and unless you've studied old circuits, yes these are pretty much gone in today's electronics. In the past amplifying devices could not deal with speakers directly due to impedance mismatch. Specifically vacuum tubes and ancient transistors cannot deal with them.

Current transistors can deal with speakers directly and thus transformers used in this manner are now obsolete.

There are other uses for transformers in speaker circuits too other than the impedance mismatch but not as frequently used anymore either (speaker multiplexing)... And one purpose that may still be used (same reason why power transmission lines are high voltage...)

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

If you're younger than around 50 years or so, and unless you've studied old circuits, yes these are pretty much gone in today's electronics.

I'm 48 and I studied electronics in a two year program at the local junior college back in 1990.

In the past amplifying devices could not deal with speakers directly due to impedance mismatch. Specifically vacuum tubes and ancient transistors cannot deal with them.

This makes sense to me ... especially when using vacuum tubes... it had to be difficult building any kind of precision into a vacuum tube back then.

Current transistors can deal with speakers directly and thus transformers used in this manner are now obsolete.

There are other uses for transformers in speaker circuits too other than the impedance mismatch but not as frequently used anymore either (speaker multiplexing)... And one purpose that may still be used (same reason why power transmission lines are high voltage...)

So can this transformer be used to step down 120V AC into something ... lower than 120???

[budm]

Re: Found a transformer at a thrift store and am curious...

It is typical line matching transformer use in PA system with multiple speakers.
Lots of solid state PA amp still comes with 70V line out.
https://www.belden.com/blog/broadcas...peaker-systems
https://www.ebay.com.sg/itm/Realisti...x/273847933272
https://www.ebay.com/itm/Realistic-3...-/113287352821
https://en.wikipedia.org/wiki/Consta...speaker_system

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

Yeah you probably never studied them unless you found a vacuum tube or ancient transistor radio and took it apart. These things were by low impedance transistor 1970s designs. The 1960s vacuum tubes and transistors were their last stand.

Problem with speakers is that they're current controlled. I*R drop due to long wires makes sense to use higher voltage in long distance speaker runs.

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

Yeah you probably never studied them unless you found a vacuum tube or ancient transistor radio and took it apart. These things were by low impedance transistor 1970s designs. The 1960s vacuum tubes and transistors were their last stand.

Problem with speakers is that they're current controlled. I*R drop due to long wires makes sense to use higher voltage in long distance speaker runs.

I remember in the 70's, we had a Zenith television in the living room ... it was a kit that my dad built. At least once a month, he was always tinkering with that thing with a mirror in front of the screen and him behind the TV looking at the screen with the mirror, tinkering with settings. The television was a large floor unit ... a piece of furniture really ... it had a real "clicker" for a remote (not sure how those worked exactly) and it had two dials that had to be mounted on a motor because the clicker would physically turn the dials one channel at a time. When it would hit U(UHF) then the UHF dial would turn until it made a rotation at which point it would go through channels 2 to 13 before hitting U again.

I remember going with him to Thrifty's quite often with a handful of vacuum tubes that he would check in their tester then sometimes hed end up buying a tube or two ...

lol ... boy im glad we're past those days....

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

Or is it better to long for those days again where the FRUs are much smaller?

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

Or is it better to long for those days again where the FRUs are much smaller?

FRUs?

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

Field Replacement Unit (i.e. replace a single transistor instead of a full PCB or even IC if a single transistor failed.)

Granted a single IC is physically smaller than a vacuum tube, but the IC probably has lots of good transistors in it

[R_J]

Re: Found a transformer at a thrift store and am curious...

Here is a new 70 volt line transformer in the box, ebay $15.00

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

BTW I missed the original question, whether it can step down 120VAC. I doubt it or at least it probably would get hot. It was clearly designed for the audio range. You're better off locating a transformer marked for line voltage use.

[redwire]

Re: Found a transformer at a thrift store and am curious...

OP you have a 10W 70 volt line audio matching transformer. It is used for bigger paging and PA speaker installations.

It is not suitable for use as a mains power transformer. It does not have high voltage isolation between primary and secondary, and at 120VAC it would be saturated. That and paper wrap is not the greatest for flammability.

The turns ratio is about 5.5:1 using the 16 ohm tap.

[PeteS in CA]

Re: Found a transformer at a thrift store and am curious...

Radio Shack speaker transformer, used to match to 16, 8, or 4 ohm speakers.

[Sparkey55]

Re: Found a transformer at a thrift store and am curious...

I don't know a whole lot about transformers beyond what they do functionally ... I've never made a circuit that incorporated a transformer so I've never had to spec one out or even figure out how they connect. The one time I tried to re-use a transformer from a circuit I connected it wrong and literally made a loud bang when I connected power to it ...

Anyways, I found this one at a thrift store for $1.25 and was wondering if it could be used to step down 120V AC ... it looks like it was used somehow in an audio circuit as each side has what looks like a Common pin then a selection of wattage and on the other side, a choice of 4, 8, or 16 Ohms, which I assume is relevant to the speaker you're connecting it to...

Why would a transformer be used in audio in the first place?

I use some that are similar to that in my R-390A receivers to match 600 ohms to 4 ohms 6"x9" speakers.

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

Field Replacement Unit (i.e. replace a single transistor instead of a full PCB or even IC if a single transistor failed.)

Granted a single IC is physically smaller than a vacuum tube, but the IC probably has lots of good transistors in it

Which ... from a design / quality perspective concerning the overall scope of the circuit, is probably a good thing...

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

Here is a new 70 volt line transformer in the box, ebay $15.00

So I got a deal at $1.25

[stj]

Re: Found a transformer at a thrift store and am curious...

only if you need it or can sell it.
otherwise your out $1.25 - you could get a nice beer for that!

[EasyGoing1]

Re: Found a transformer at a thrift store and am curious...

only if you need it or can sell it.
otherwise your out $1.25 - you could get a nice beer for that!

Tell me please where I can get a NICE beer for $1.25 .... anywhere ....

[stj]

Re: Found a transformer at a thrift store and am curious...

i just drank one - a Shepard Neame "Bishops Finger"

[eccerr0r]

Re: Found a transformer at a thrift store and am curious...

Which ... from a design / quality perspective concerning the overall scope of the circuit, is probably a good thing...

However from a enduser repair point of view, you have to get the exact same IC instead of the possibility of substitutions and jury rig fixes...

I guess my fix count of stereo amplifiers is now 2. One of them I had to buy the STK IC module to repair it, the other I just took a random (well not totally random) transistor and stuck it in... both now fixed. The first one I had to wait weeks before I got the part. The second one I had an acceptable substitute in my junk bin. Not a perfect substitute but it still works nevertheless.

The IC solution probably is cheaper to produce as there's no need to tweak pots to align the amplifier - all done for you. So basically it's all a matter of assembly costs. But when it fails, time to locate a possibly unobtainium IC...