Any information about mini transformer ?

Thread Starter

Externet

Joined Nov 29, 2005
1,957
Hi.
An audio oscillator uses a miniature transformer labeled 6T-190K. Looks like one of those used in very old portable transistor radios :

1669931825793.png1669932364898.png
Trying to find any information about it, or the replacement, or equivalent, or whatever can be found. There used to be a web site dedicated to them with hundreds of their brands, part numbers and applications that cannot locate now :(
Any assistance is appreciated.
 

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KeithWalker

Joined Jul 10, 2017
2,604
If you have small transformers with no information about them, there are several things you can find out about them:
Inspect the construction of the laminated core. If the laminations are interleaved, it is designed for AC circuits only, e.g. push-pull output circuits. If the laminations are assembled as E and I, it is for use in a circuit where a DC current will be passing through a winding, e.g. as a transistor load and there will be a small gap between the sections to prevent the core from becoming saturated by the DC current
Measure the resistances between all of the pins, then you will know how many windings it has and whether there are any taps on any winding. If there is a winding with fairly low resistance (a few ohms) it is probably an output winding for driving a speaker.
The turns ratio is measured by connecting a signal source across the higher resistance winding and measuring the amplitude of signal appearing across each winding. We can assume that these are audio transformers, so use a signal somewhere between 600Hz and 1KHz.
From their physical size, I would guess that they are made for handling up to a couple of hundred milliwatts.
 

Ian0

Joined Aug 7, 2020
6,662
They are drive transformers and output transformers for early transistor amplifiers.
The red one is the output transformer and is generally called Eagle LT700.
The blue one is the drive transformer and it is 10k: 1.2k centre tapped.
I don't know about the white one.
They are really only telephone bandwidth (about 300Hz to 3kHz)
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
Thanks.

Are you trying to build something from vintage plans, or repair an existing oscillator?
Am trying to duplicate = copy exactly a circuit from the eighties which uses a 6T-190K labeled transformer; several other tranformers tried do not work as the original.
 
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bassbindevil

Joined Jan 23, 2014
624
Telephone answering machines and computer modems usually have audio coupling transformers, possibly 1:1 600 ohms. I bought a couple of transformers like that from Radio Shack when making my own modem seemed like a good idea.

Can you provide a link to the project article or post a scan? Did they give a source for the transformer?
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
Thanks, bassbin. Not a published project, contacted the manufacturer: responded they stopped 30 years ago making the oscillator, no parts nor source left available for it and no data published. :confused:
The only thing am left with is the 6T-190K unobtanium numbering that shows up nowhere. :(

I have a couple of dozens canibalized from telephones, transistor radios, modems... None performed.
 

bassbindevil

Joined Jan 23, 2014
624
I guess the only hope is to fully understand the circuit and work out what the transformer needs to do. Or borrow an oscillator and measure the transformer. Or if you're a character in a TV show, sneak into the manufacturer's factory and snoop through their archives. Or if there's a name or initials on the schematic drawing, find that person; maybe they have design notes in their personal files or can remember some crucial details.
 
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panic mode

Joined Oct 10, 2011
2,360
there are many ways to create an audio oscillator. many of them need no transformer. why don't you post some specs that it should have or post the schematics of the oscillator you are trying to build
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
there are many ways to create an audio oscillator. many of them need no transformer. why don't you post some specs that it should have or post the schematics of the oscillator you are trying to build
Thanks . I do not want to create AN audio oscillator.
Am after duplicating/making exactly the one like in post #7 at ----> https://forum.allaboutcircuits.com/threads/blocking-oscillator.170252/

L3 + L4 which are in series replaced by a single 8 ohm 2" tiny speaker... L1 and L2 being the audio transformer. Produces sine wave as in the second plot. And works on 1.3V !

Had to delete the 'similar' schematic as responses were misled instead of the one on link.
 
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KeithWalker

Joined Jul 10, 2017
2,604
Thanks . I do not want to create AN audio oscillator.
Am after duplicating/making exactly the one like in post #7 at ----> https://forum.allaboutcircuits.com/threads/blocking-oscillator.170252/

L3 + L4 which are in series replaced by a single 8 ohm 2" tiny speaker... L1 and L2 being the audio transformer. Produces sine wave as in the second plot. And works on 1.3V !
You can make a blocking oscillator as shown in your diagram very easily using just about any audio transforme that has two saperate windings. The only problem is that you want to drive a speaker from the same transformer. Most transformers that have a low impedance winding for driving a speaker have a center tapped primary, which will not work in your circuit.
There are several solutions to your problem:
1: Find a transformer designed for a push-pull output stage that has two separate primary windings which, as you have found out, are very rare.
2: Wind your own transformer.
3: Add an output winding of a few turns to an existing 1:1 transformer.
4: Use a capacitor to couple the output from the collector of the transistor to a second transistor that drives the speaker.
5: Use a different circuit for your blocking oscillator.
 

Danko

Joined Nov 22, 2017
1,487
Thanks . I do not want to create AN audio oscillator.
Am after duplicating/making exactly the one like in post #7 at ----> https://forum.allaboutcircuits.com/threads/blocking-oscillator.170252/
L3 + L4 which are in series replaced by a single 8 ohm 2" tiny speaker... L1 and L2 being the audio transformer. Produces sine wave as in the second plot. And works on 1.3V !
Below is circuit of transformerless sine audio oscillator.
Very loud because it works on speaker mechanical resonant frequency.
Highly efficient, because transistor Q2 operates in switching mode.
Smaller speaker - higher oscillations frequency.

1671997900862.png_____1671998323892.png
 

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PaulEE

Joined Dec 23, 2011
474
To the OP in particular:
Xicon transformers are available on Mouser. If you measure the resistances on the windings, I'm sure you can find one similar to yours by looking at the choices on the datasheet linked here, or by searching Mouser. 164278 (Page 1) (mouser.com)

Paul
KI5VNH
 
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