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Old 17th March 2011, 01:52 PM   #51
kevinkr is offline kevinkr  United States
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Quote:
Originally Posted by pieter t View Post
Hi Kevin,

Checking HA-133 specs I see that primary impedance is indicated being "15k".
We know that transformers in general have no "impedance", but impedance ratios, however I prefer "winding" ratios.
All one can say is that a "15k" primary impedance asks for a minimum value of primary inductance. Though the absolute value measured by some inductance bridge does not tell us everything it gives an indication, and I would say that the HA-133 should have at least 150H. It is a pity that UTC did not give specs of primary L.
Did you ever measured it?
Unfortunately I have no means of accurately measuring it, but my one attempt long ago did indicate that it had a higher primary inductance than I could measure at the time which was 100H..(I've heard technically unsubstantiated comments to the effect that it is in the >170H range.) The winding ratio is ~ 5:1 which obviously depends on the taps chosen on the secondary side, but for the 500/600 ohm taps that's the ratio. I'm not sure why it didn't occur to me at the time to measure the inductance of one half of the primary as that should have been well within the range of the meter I was using, (at 1/4 of the total inductance) but I didn't. (The only working meter I have now is good for only 20H, and the bridge which can do 200H is not in working order, and probably won't ever be.)
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Last edited by kevinkr; 17th March 2011 at 02:00 PM.
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Old 17th March 2011, 03:39 PM   #52
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you can measure the secondary and multiply that number by 25 (assuming it is indeed 5:1)

dave
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Old 17th March 2011, 03:53 PM   #53
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Originally Posted by dave slagle View Post
you can measure the secondary and multiply that number by 25 (assuming it is indeed 5:1)

dave
Hi Dave,
In theory by measuring secondary inductance you can calculate primary inductance, sure (1H of measured secondary L should be 25H primary L in case of 5:1).
In practice however it does not apply very accurately; I often check this and actually never find that the relation is 100% accurate, but nevertheless of course it should give enough info for practical purposes.
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Old 18th March 2011, 05:26 PM   #54
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Hello iron guys,

I have a quick question regarding grounding or not of the frame of plate chokes. I'm just wiring up a couple of Hammond 125C plate chokes, which are open frame and held by the usual C shaped clamps. Now, the whole of the clamp is coated with varnish so it's non-conductive. Why so? Is this an indication that the frame should be floating and not earthed? Or should I scrape away some of the varnish and ground the clamps to the chassis? Amongst other things, thinking of hum here.

Andy
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Old 18th March 2011, 06:46 PM   #55
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Hi Andy,

I generally make sure that each metal part is grounded. Saftey precautions would also recommend this practice.

This can also impact the frequency response depending on how the choke is wound.

This can be easily seen with a frequency sweep in both grounded and ungrounded condition. Depending on the construction of the choke, it can also have an influence which way around you connect the choke.

Best regards

Thomas
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Old 4th May 2012, 02:02 PM   #56
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Hello guys,
I am just wondering if any of you knows aprox. the primary inductance of the
UTC A-25 transformers...
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Old 9th May 2012, 10:26 PM   #57
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Quote:
Originally Posted by andyjevans View Post
Hello iron guys,

I have a quick question regarding grounding or not of the frame of plate chokes. I'm just wiring up a couple of Hammond 125C plate chokes, which are open frame and held by the usual C shaped clamps. Now, the whole of the clamp is coated with varnish so it's non-conductive. Why so? Is this an indication that the frame should be floating and not earthed? Or should I scrape away some of the varnish and ground the clamps to the chassis? Amongst other things, thinking of hum here.

Andy
Reading David Davenport's article on Grounding, leads to the conclusion that it should be isolated from the chassis and "grounded" to the power common, like an output transformer.

btw I do have a pair of the plate chokes you referenced from eBay, and also a pair of the vt4c.com "200H 30mA" chokes, plus three pairs of big 78 lam chokes I had wound years ago. I never got around to trying any of them, especially not with a 26, but if you are interested you could test them out.

Simon
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