15-06-2012, 05:41 PM
I have found another problem....One of the loss balancve pots is o/c at one end, both of these dual gang pots are rigged up as rheostats and not dividers so I swopped both end connections round which is fine but obviously the loss balance scale is back to front, my main interest in this gear is uH inductance measurement and uuF capacitance measurement so that scale does not matter so much as it is all relavent to the fixed 1Khz bridge frequency.
The section of the loss balance pot that is o/c at one end is 17k W.W so soon as I get a set of imperial allen keys I shall take it out and see if I can repair it, undoing a couple of turns of the resistance wire andreconnecting should not affect things to much, if I get round to doing this I shall report the results whatever they may be.
The 2.4 R resistor that was o/c has now got a 10 R and an 18 R carbon composition in parallel as a temporary fix which gives just under 7 R not ideal but the bridge works and balances even with that value, shorting the old resistor out works ok on all the ranges except the lowest, as shorting it out stops the osc.
I have tried various known values of resistors and capacitors and it's spot on, with no test component connected the bridge when set to the lowest capacitance range balances out at exactly zero pf.
I have tried inductors from 3 mh down to 2 uh and the results for the single layer coils which were mainly home wound agree with the values that have been worked out via various online inductance calculators, so all seems fine there.
So all in all despite the couple of faults this bridge is accurate and easy to use, managed to get a PP9 from Halfords.
The bridge is still running with it's GET 102's and OC 200 transistors.
Lawrence.
The section of the loss balance pot that is o/c at one end is 17k W.W so soon as I get a set of imperial allen keys I shall take it out and see if I can repair it, undoing a couple of turns of the resistance wire andreconnecting should not affect things to much, if I get round to doing this I shall report the results whatever they may be.
The 2.4 R resistor that was o/c has now got a 10 R and an 18 R carbon composition in parallel as a temporary fix which gives just under 7 R not ideal but the bridge works and balances even with that value, shorting the old resistor out works ok on all the ranges except the lowest, as shorting it out stops the osc.
I have tried various known values of resistors and capacitors and it's spot on, with no test component connected the bridge when set to the lowest capacitance range balances out at exactly zero pf.
I have tried inductors from 3 mh down to 2 uh and the results for the single layer coils which were mainly home wound agree with the values that have been worked out via various online inductance calculators, so all seems fine there.
So all in all despite the couple of faults this bridge is accurate and easy to use, managed to get a PP9 from Halfords.
The bridge is still running with it's GET 102's and OC 200 transistors.
Lawrence.
