UTC LH-519/FH-757 xfmr info? - diyAudio
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Old 3rd January 2012, 02:18 AM   #1
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Default UTC LH-519/FH-757 xfmr info?

Hi:

I have a pair of UTC transformers marked FH-757 and North Atlantic 202348.
I found an expired auction on eBay for UTC LH-519 transformers that also displayed North Atlantic 202348 so I know they're equivalent.

They are marked 10k ct: 5k ct, 50 cps - 20 kc, 0.13W

I'm curious if these might be usable as tube/valve interstage transformers, and if so, what kind of DC current would be reasonable.

I found a schematic for the North Atlantic Instrument they were used in and they were used in a (solid-state) phase angle voltmeter, so I cannot infer what kind of DC current they might tolerate, or make too many analogies to tube circuits.

P=E^2/R for 10k and 130 mW = 36 v...not too encouraging, but I don't know what the power rating context was.

Thanks for your thoughts.

Murray
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Old 4th January 2012, 11:18 PM   #2
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I found a Philco Radio history site that had a post recommending capacitor coupling to a IS primary to eliminate the DC. for longer life (probably referring to already-ancient radios).

That's another option...if they can handle much voltage...
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Old 11th February 2012, 06:51 PM   #3
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I think these are not intended for tube/valve voltage levels...so they must wait for another opportunity to surface...
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Old 27th January 2014, 08:27 AM   #4
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I'm trying a pair of these as I/V converters in a CS4397 DAC project. So far they are pretty good - no measurements yet but the system is built and I'm comparing them against a few others I have onhand: Hammond 850G, 804, etc.

The DAC is based on a CS4397 evaluation board I had on my parts shelf, and loosely modeled on the digital input section of Andrea Ciuffoli's project here:

Hi-End Transformer-Coupled Tube Headphone Amplifier With Digital Input by Andrea Ciuffoli

Anyway, so far so good with the UTC FH-757 tx units in this application. They're in and working at least. I seem to like them turned around backwards wired with secondaries as primaries and primaries as secondaries. I need to do some measurements on them still as part of the comparison project.

PM me if you want to discuss more?
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