Impedance bridge TF-373S , Marconi-Ekco

[JacKam_]

I am planning to repair and calibrate it, but so far I couldn't find a manual.

I wonder if anyone has at least schematic diagram.

The next question is: would it be worth of restoration, even if I had to do some reverse engineering job? If we decided yes, I will start the process.

Thank you,

Jacek

[trh01uk]

Jacek,

Yes, I have a manual which includes a schematic. Its in poor condition, but I will post it on here as soon as I can.

You ask "would it be worthy of restoration"? Well, that depends. If you want it as an instrument to measure resistors, capacitors and inductors, I would say no. You will get far better results with a modern instrument - and very good ones can be picked up second hand on Ebay. Many of these give automatic measurements in a fraction of a second. And the accuracy of this old monster is very poor - the manual says +-2.5% for resistors. An AVO can usually do better than that!

But the other aspect is whether it has historical value as an early example of this type of instrument? The date on my manual appears to be February 1944. If historical research showed this was a first for a British instrument of this type - then yes, its certainly of historical value. I have never come across an earlier version of an impedance bridge, but then I have never investigated the question. Someone else on here may know more.....


Richard

[trh01uk]

Jacek,

here is the manual that I have for the TF373D.

I did notice a couple more interesting things in the manual. There is a date of 13th April 1940 on the schematic. There is an even earlier date of 23rd September 1938 on the "basic schematic" which shows the principles of the bridge system. I suspect this is pretty early for a British designed and made instrument. I have seen very little pre-war British test equipment, though I presume there must have been some about in the best equipped labs. Those I have spoken to who remember that far back have told me that they had to make most of their own equipment - and many had no more than a "testmeter". Some even had to put up with soldering irons heated in a coal fire.....!

In terms of calibration I would start with the "standard" parts in the bridge circuits. Things like the 100 ohm "standard resistor". I think these define the calibration of the instrument.


Richard

[trh01uk]

Jacek,

I have just noticed that you asked about the TF373S - and I have given you the manual for the TF373D. No idea what the difference is. Maybe you can determine that and tell us.


Richard