Marconi TF2700 LCR bridge and measuring iron-cored chokes - diyAudio
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Old 16th March 2007, 02:58 PM   #1
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Default Marconi TF2700 LCR bridge

Does anyone own this bridge?
I'd like to do some questions on this instrument.
Or better have the manual.

It looks like a good bridge and sold in a good price on e-bay.
I'm thinking seriously to buy one.............
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Old 24th March 2007, 01:37 PM   #2
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Noone owns a Marconi bridge?
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Old 28th March 2007, 09:55 AM   #3
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I do. It is an excellent bridge. What do you need to know?
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Old 28th March 2007, 02:07 PM   #4
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wow I have posted this subject many days ago. Almost I forgot it!
And............. an answer from a person I respect!
I'm missing a long time from the boards.But I remember you from the "tubes" section.

I don't have a bridge and there are a lot of times that I'd like to measure capacitance and impedance.
I'd like to know if it can measure choke and primary impedance of an OPT.
But my problem is to measure a choke, say at 50Hz and 200mA
an OPT at 20Hz and 50mA. Also does it apply any high voltage to the measured coil?
Not a problem if it needs an external signal generator or current source.
It will be helpfull if you can send me a copy of the Marconi's manual.....
Thanks
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Old 28th March 2007, 06:48 PM   #5
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You're very kind.

The TF2700 can measure:

Primary inductance of an output transformer.
Inductance of a choke with DC applied but it needs an external constant current source to apply the DC. It is also best if you give it an external source of AC so that it can measure smoothing chokes at 100Hz.
Air-cored crossover chokes (best done at 20kHz).
And it's very good for measuring capacitors (not so good for electrolytics).

There's really rather a lot of the manual, and scanning it would be a lot of work; just make sure you get a manual when you buy the bridge.
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Old 28th March 2007, 07:33 PM   #6
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yup the correct name is inductance!
sorry but I'm not good with english.

So, with an external cs you can apply the desired mA.
And with an external source of AC you mean a signal generator?
What about voltage? Can you apply an external high voltage to the choke?
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Old 28th March 2007, 08:51 PM   #7
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I'm not sure why you'd want to apply a high voltage to the choke (other than to check for breakdown) - it's a current dependent device.

Don't worry about your English, my French would have a Frenchman in tears.
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Old 28th March 2007, 09:55 PM   #8
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Isn't better to measure it under conditions similar to which the choke is used.
I read this to Radiotron D Handbook.....
Do you have it? (pg250)
It says that "the value of inductance depends to a marked degree on the ac flux density in the core and also on any dc flux set up in the core by direct currents in the windings"
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Old 29th March 2007, 06:45 AM   #9
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You are absolutely right - a test should as closely as possible replicate the conditions of use. And as RDH4 says, the flux in the core of an inductor markedly changes the inductance, so you need to be able to vary that. But that's down to current not voltage. Here's one I measured earlier...
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Old 29th March 2007, 02:04 PM   #10
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I know that inductance changes with different applied currents but....................
Can you do a test with a constant current and a variable applied voltage?
Just to see the differences.If there are any!
I believe you but I'm just wondering what happans if the voltage is variable.
I don't have the instruments to check it.....

I thing I'll hit a Marconi TF2700 bridge! I like the old style design too!
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