05-03-2019, 06:35 PM
Roger,
Yes, it is Charles.
I use Chas in many forums, seems it was available...
I have capacitance meters, most are old school bridge type.
You will find that long leads will become part of the measurement. In open space, 8" clips leads will give 10pf, twist the leads together and it will go quite a bit higher. So it is best to measure right at the binding posts.
Caps that are leaking a LOT will have a very broad and slight wink to the eye. The overall quality of the cap is indicated by how sharp/deep the null. Really, should not be used to evaluate quality, just the ball park value and leakage under high voltage.
I keep a couple of 1% cap values as standards on the bench, in event I get a out of whack reading...
I found that as I service, I don't bother with common paper caps, just replace. Others that seem questionable and may be a more modern cap I will measure.
Truth be said I seldom use the bridge. It gets pressed into service when the radio won't align, generally, mica fixed padders are off or coil forms have shrunk. So I have to measure to know how far to pad out a cap to achieve alignment.
Oh, I do not know the full functions of the Eico, but if places over 600 volts on the cap, be careful. A large cap can recover some of the charge even after discharge in the bridge. Painful. Fair warning, it is not good for an ordinary cap over 1 mf to be discharged by shorting. The high current flow can breakup metalizing on those types or the internal connections on those with foils. Caps used in camera flashes can take it but still should have a resistor to discharge.
Useful tool...
Chas
Yes, it is Charles.
I use Chas in many forums, seems it was available...
I have capacitance meters, most are old school bridge type.
You will find that long leads will become part of the measurement. In open space, 8" clips leads will give 10pf, twist the leads together and it will go quite a bit higher. So it is best to measure right at the binding posts.
Caps that are leaking a LOT will have a very broad and slight wink to the eye. The overall quality of the cap is indicated by how sharp/deep the null. Really, should not be used to evaluate quality, just the ball park value and leakage under high voltage.
I keep a couple of 1% cap values as standards on the bench, in event I get a out of whack reading...
I found that as I service, I don't bother with common paper caps, just replace. Others that seem questionable and may be a more modern cap I will measure.
Truth be said I seldom use the bridge. It gets pressed into service when the radio won't align, generally, mica fixed padders are off or coil forms have shrunk. So I have to measure to know how far to pad out a cap to achieve alignment.
Oh, I do not know the full functions of the Eico, but if places over 600 volts on the cap, be careful. A large cap can recover some of the charge even after discharge in the bridge. Painful. Fair warning, it is not good for an ordinary cap over 1 mf to be discharged by shorting. The high current flow can breakup metalizing on those types or the internal connections on those with foils. Caps used in camera flashes can take it but still should have a resistor to discharge.
Useful tool...
Chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
