I bought a pair of vintage Telefunken OPT's from a nice woman in Germany. They were originally from a Magnetephon reel to reel. SE wtih EL95 output tubes. I tested them with two different ohm meters and all the windings show infinite resistance. I applied a 3.5 volt AC sine wave to the white/yellow and green/brown primary windings and measured nothing at the red/blue secondaries. She insists the transformers were good when she shipped them. Is there something wrong with the way I'm testing them or are they just junk?
I don't understand what measurement requires TWO ohm meters.
How did you determine which wires are for primary and secondary ?
Have you measured all colour/wire-combinations ?
It is unlikely that both transformers are damaged identically, i.e. both primary and secondary windings broken.
artsalo, it doesn't seem logical that both transformers could fail in exactly the same way. I tried using each wire as a starting point and found no continuity anywhere, not even to the case, which seems weird. The yellow/white and brown/green wires are very tiny. I'm assuming high voltage low current. The red/blue are thicker single strand, Which I assume are higher current lower voltage outputs. My signal generator is only capable of 3.5 volts AC. The one thing I haven't tried is using the variac to test them.
Maybe you should use a magnifier to see if there's enamel, oxides, plastic or anything that prevent the DMM to make contact with those leads. I would scrape the leads with a knife, pickle them with flux or rosin and then tinker the ends. Only after this job you will be sure your DMM makes contact with the leads. Tell us if you had success.
Once I bought a pair of Zenith speakers and they were not functioning at all. I checked the cables (the original old cables), they were conducting. I changed the cables with new ones and the speakers worked! So you can expect anything from a pair of old transformers.
Once I bought a pair of Zenith speakers and they were not functioning at all. I checked the cables (the original old cables), they were conducting. I changed the cables with new ones and the speakers worked! So you can expect anything from a pair of old transformers.
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Seems likely to me that there is insulating varnish on those wires, try tinning them and then remeasuring.
Primaries do go open under fault conditions, but this is exceedingly rare with the more robust windings found in the secondary.
These should be pretty decent transformers if they are OK.
Seems likely to me that there is insulating varnish on those wires, try tinning them and then remeasuring.
Primaries do go open under fault conditions, but this is exceedingly rare with the more robust windings found in the secondary.
These should be pretty decent transformers if they are OK.
Yes, if there are only enamel coated wires and no terminals, then scrape off with a sharp blade the very end of the wires for a small distance
to allow a probe to make contact for measurement. Soldering may not remove the enamel.
Maybe the transformers' leads were cut instead of desoldered when removing from the unit.
YES! Thats it! I scraped the leads and they test good now. I understand what Telefunken did. The color coded insulation on the wires fits very loosely. I thought that was strange. What they did was to extend the winding wire out of the transformer and then slip the plastic over it. Eliminating the need to solder leads to the winding wire. Thanks very much everyone for the help. The woman that sold them to me seems very nice. I'm so happy that I can tell her the transformers are good. Happy holidays everyone!
Hey does anyone know anything about these transformers? They are supposed to be SE EL95 transformers from a reel to reel. They seem to have two primaries and a single secondary. The primaries have radically different turns ratios. Is it possible that one is for the plate and the other the screen? I can't seem to find a schematic?
As I recall one of the secondary windings is for driving a speaker, and the other IIRC for driving the record head. These little transformers sometimes have a hum cancelling winding.
Email the lady you purchased them from and ask for the model of the tape recorder they were removed from. You should then be able to locate the proper schematic.
Email the lady you purchased them from and ask for the model of the tape recorder they were removed from. You should then be able to locate the proper schematic.
You can probably get some ideas about Telefunken output stages by looking at some of the Telefunken radio/phono schematics
Perhaps something like this?
That one has two secondaries and one primary, but perhaps there are other styles as well...?
EDIT:Kevin replied with the 'real answer' while I was typing...there ya go...
EL95 or EL42 are not as easy to find, unless you already have them, you could try with a 6AQ5 (EL90) which are really cheap and they sound great, they should work nicely with those transformers.
Perhaps you'll have to play a bit with the secondary impedance to reflect about 8 to 10k at the primary, for that you will have to find out the turns ratio.
Perhaps you'll have to play a bit with the secondary impedance to reflect about 8 to 10k at the primary, for that you will have to find out the turns ratio.
Many of the tube reel tape recorders had two secondary windings on the OPT. One for the internal speaker/phones, and one for a remote extension speaker.
If you need EL95s I have plenty of NOS ones. They were common out here in tube AM car radios.
Gary
Hey All,
I think Kevin is right. The white/yellow output is really low (maybe the tape head output KR was talking about?). But the other winding is a little strange? When I input 3.66 volts AC into the red/blue wires I get .598 out of the brown/green. 3.66/.598 = 6.12, 6.12 x 6.12 = 37.45. The only way this impedance ratio makes sense is if it is a headphone output? 37.45 x 300 = 11.2k Or is my math wrong?
Kevin
I think Kevin is right. The white/yellow output is really low (maybe the tape head output KR was talking about?). But the other winding is a little strange? When I input 3.66 volts AC into the red/blue wires I get .598 out of the brown/green. 3.66/.598 = 6.12, 6.12 x 6.12 = 37.45. The only way this impedance ratio makes sense is if it is a headphone output? 37.45 x 300 = 11.2k Or is my math wrong?
Kevin
Are you sure it is .598 and not .00598 ? anyway to make sure, you could try the other way, if you have low voltage and high current transformer, say 12 volts 1 Amp connect that to the secondary and measure the primary (you might get something like 200+ volts so be careful), or try a higher voltage transformer of about 100 to 200 volts AC in the primary and you'll get above 1 volt so your measure will have less digits to deal with.
The smallest gauge wires will (probably) be the primary, and the large gauge wires will be the secondaries, with the largest gauge likely being the speaker secondary.
Don't assume you know the color codes on the wires of these transformers, Germans did not often follow U.S. conventions. Based on your description I would suspect the red and blue wires are the speaker secondary.
Don't assume you know the color codes on the wires of these transformers, Germans did not often follow U.S. conventions. Based on your description I would suspect the red and blue wires are the speaker secondary.
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