Triad 3758 Transformer ID help

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thecr4ne

Well-known member
Joined
Aug 26, 2016
Messages
239
Location
California
Hi all,
Looking for specs on these. Unfortunately the few old Triad catalog pdfs I have found don't have anything on these. They say triad and have 3758 printed on them, but no specs.

Anyone have any clue?
s-l1600.jpg
 
CJ said:
probably mic or  line input if it has gold pins,

80 bucks on evilbay?

That's what I'm hoping for...as for price, about half that. One might be able to go lower. Seller has a lot of them and accepted my best offer (actually countered with a price $0.01 less per pair...first time I've ever gotten a better counter than my own best offer)
 
These arrived yesterday. I poked at 2 of them a bit with my multimeter and here's the early results

Pins 8-2: 3.62k/3.65k Center tapped at Pin 1
Pins 8-1: 1.97k/1.98k
Pins 1-2: 1.64k/1.65k

Pins 3-4: 5.21k/5.25k

Values are just direct DC resistances. Nothing seems tied to the can.

Hoping to get my act together at some point to work through Pucho's Transformer measuring guide. but if this is enough to ring any bells, let me know.


 
With those huge DCRs, I smell geo-transformer.

Through the 1950s there was much work with with seismographs and particularly oil exploration by recording echos through the rocks. These need very extended "bass" response, to below 1Hz; treble was sacrificed.
 
could be single plate to push-pull grid innerstage,

check voltage ratio, should be around 1:2  if innerstage,

never seen an octal geoformer,  or a geoformer with a CT, usually balanced dual coils for series or parallel,

do not think they would use gold pins either,  and if the geoformer is being towed underwater, they would want a solid connection, not an octal socket, so do not lose hope just yet, check freq response if you have the means,
 
Any considerations to be taken into account for the high resistance or would I go about it like a line level transformer?

For voltage ratio, run 1kHz through it at 1V or so and measure output voltage right?

And for the freq response, white noise in and out to a spectrum analyzer?

Forgive me, I'm somewhat new to the wonderful world of inductors. 
 
Ok, I did what I could on one of these with fewer alligator clips than I would've liked. I'll dig for some more leads and try again tomorrow.

So, if I've done things correctly, Voltage ratio is 1:1, or considering the center tap 2:1+1. To clarify, 1kHz at 1V in to pins 3-4 measures 1V on pins 8-2, and 0.5V on pins 8-1, 1-2

I ran a few tests with Rightmark audio analyzer and ended up with some encouraging results. Below is a frequency response graph comparing the wiring it "backwards" and "forwards" the white line is pins 3-4 as the primary, 8-2 as secondary, the green plot is 8-2 primary and 3-4 secondary. Let it also be noted that the input gain knob on the USB interface was at about +4dB using pins 3-4 as the primary, and at about +40dB using pins 8-2 as the primary.

Based on the plot, I think it's safe to say this is an audio transformer, primary across pins 3 and 4, secondary across pins 8 and 2, center tapped at pin 1. Can we infer a rough idea of the impedance ratio from the input gain difference? I don't have many pots/variable resistors handy to actually measure it. I'll try to play with this more tomorrow if there's time.

Would love any feedback re: my results and/or any flawed logic or methodology.

Here's the plot:
t3eNYA2.png







 
Found in the 1962 Triad catalog. So far the closest lead I have.

Octal case is "P" case. of the few models with that case, the A-210P looks closest. Ratio is right, DC resistances look like they're at least in the same universe, though not dead on. Size looks right, but I don't have them in front of me to measure.

"Isolation for Stereo Amplifier-To eliminate ground loop disturbance"


TR-62%20pg-016.jpg
 
thecr4ne said:
Would love any feedback re: my results and/or any flawed logic or methodology.

Here's the plot:
t3eNYA2.png

What’s the input impedance of your interface and the output impedance of your signal gen? I’d assume maybe 10k for the interface input and 50 ohms for signal gen output. Did you play with series resistors on the input, or terminating resistors on the output? If you’re right about this being the model in the catalog (or similar), the matching impedances it was designed for are quite a bit higher on both windings. 27k is kind of an unusual design impedance for what we usually do here.

600:600, 10k:10k or 15k:15k would be more typical use cases for a 1:1 transformer.  Maybe make some plots using those impedances to get a better idea about what you could do with the thing.

It’s pretty small (maybe ouncer size). I’d be surprised if it could take much more level than +8 dBm. Consider that in the uses you try it in. Run a 20 Hz signal through it while looking at the harmonics in Rightmark, and increase the signal level until you start to see a visible rise in the harmonics in relation to 20 Hz (or a visible rise in the higher order harmonics). That’ll give you a very rough idea of the levels the thing can take.
 
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