Marconi TF2700 Bridge

[pwdrive]

I understand, all clever stuff.

Lawrence.

[coil1234]

I've also got a TF 2700 here, which was rescued on its way to the skip at work.
It had never seemed 'quite right', often giving conflicting readings.
As an ex calibration engineer I've got a thing about reliable test gear, so I did a blanket change of all the electrolytics and carbon resistors as well as cleaning all the switches.
Although much improved it still intermittantly gave the wrong readings with certain values of component, this turned out to be R10, the 600 ohm 0.1% WW in the balance arm
So, with nothing left to lose I unwound it then re-wound it! Hoping that the poor insulation would not end up touching again. To make things more dificult it was counterwound (for low inductance) and took the best part of a morning with several yards of cotton covered resistance wire looped around the house!
However it worked and is good reliable instrument.

Anyway, what this is leading up to is that if Laurence requires a 2.4 ohm resistor I'll stick some in the post.

Regards Mike A

[Skywave]

. . . . and took the best part of a morning with several yards of cotton covered resistance wire looped around the house!

Mike A

Now that is what I call true dedication to The Cause! Well done, sir!

Al.

[pwdrive]

I've also got a TF 2700 here, which was rescued on its way to the skip at work.
It had never seemed 'quite right', often giving conflicting readings.
As an ex calibration engineer I've got a thing about reliable test gear, so I did a blanket change of all the electrolytics and carbon resistors as well as cleaning all the switches.
Although much improved it still intermittantly gave the wrong readings with certain values of component, this turned out to be R10, the 600 ohm 0.1% WW in the balance arm
So, with nothing left to lose I unwound it then re-wound it! Hoping that the poor insulation would not end up touching again. To make things more dificult it was counterwound (for low inductance) and took the best part of a morning with several yards of cotton covered resistance wire looped around the house!
However it worked and is good reliable instrument.

Anyway, what this is leading up to is that if Laurence requires a 2.4 ohm resistor I'll stick some in the post.

Regards Mike A

That's the spirit Mike, excellant stuff. As regarding the 2.4 R resistor I should be ok sourcing one, the original is a carbon comp. type 5% so should be no pproblem, thank you very much for your offer though.

Lawrence.

[Yorkie]

If you're stuck for a particular value - as often happens for meter shunt resistors - apart from winding your own from resistance wire (assuming that it won't matter if the resistor is inductive), it's always worth considering using a couple of resistors in parallel from the more common E12 range. EG: 6.2R + 3.9R = 2.394R (99.75%). 6.8R + 3.9R = 2.478R (103.25%)

Lots of parallel resistance calculators on t'internet to take the pain out of doing the calculations! EG: http://www.1728.org/resistrs.htm