22-07-2020, 11:57 AM
How did I know how far wrong the Silver Mica caps were?
Previously I only remember replacing SM caps when they had loose rivets or other obvious damage.
I have a precision LC meter based on a PIC and kit, that has a relay and uses a 5000pF capacitor as a reference. I bought it maybe 15 years ago, only buying the PCB and pre-programmed PIC. A year or two later I bought a better, one the AADE model in work. I don't have it. My friend near Limerick with loads of gear had an expensive thing with either 0.1% or 0.05% accuracy, I forget. He also had a box of 350V epoxy encapsulated 5000 pF 0.5% caps. Maybe SM. So one of them went in and he gave me a small handful of others that tested close to 5000 pF, though not as close as the one selected for the reference. Mostly as good as the 0.5% on the label.
So I rechecked it, my DMM which reads about 1nF with nothing connected, a bare Chinese universal component tester, a dedicated Chinese DM6293L (which does maybe 200H max), and I have an old Bridge, like the Hunts style of thing. It's neon is hidden inside, instead the Y63 magic eye used to null bridge is the leakage display. The precision kit was bought as it sensibly measures VHF coils and capacitors maybe below 1uH and 1pF at the terminals. You can press Calibrate on C (open) or L (short) to zero the display for probe lead capacitance or inductance.
Measuring the 5000pF picked at random, in stock maybe 15 years:
Precision kit: 5060 pF (I should have removed leads and used terminals)
Chinese Uni: 5044 pF
DMM (ΔRel): 4980 pf (Using regular leads, and hitting ΔRel button before connecting DUT.
DM 6243 L : 4960 pF (On terminal socket rather than leads)
Old Bridge: 4600 pF approximately. It's a pot with a big perspex pointer on the 1 to 10 scale.
Previously I only remember replacing SM caps when they had loose rivets or other obvious damage.
I have a precision LC meter based on a PIC and kit, that has a relay and uses a 5000pF capacitor as a reference. I bought it maybe 15 years ago, only buying the PCB and pre-programmed PIC. A year or two later I bought a better, one the AADE model in work. I don't have it. My friend near Limerick with loads of gear had an expensive thing with either 0.1% or 0.05% accuracy, I forget. He also had a box of 350V epoxy encapsulated 5000 pF 0.5% caps. Maybe SM. So one of them went in and he gave me a small handful of others that tested close to 5000 pF, though not as close as the one selected for the reference. Mostly as good as the 0.5% on the label.
So I rechecked it, my DMM which reads about 1nF with nothing connected, a bare Chinese universal component tester, a dedicated Chinese DM6293L (which does maybe 200H max), and I have an old Bridge, like the Hunts style of thing. It's neon is hidden inside, instead the Y63 magic eye used to null bridge is the leakage display. The precision kit was bought as it sensibly measures VHF coils and capacitors maybe below 1uH and 1pF at the terminals. You can press Calibrate on C (open) or L (short) to zero the display for probe lead capacitance or inductance.
Measuring the 5000pF picked at random, in stock maybe 15 years:
Precision kit: 5060 pF (I should have removed leads and used terminals)
Chinese Uni: 5044 pF
DMM (ΔRel): 4980 pf (Using regular leads, and hitting ΔRel button before connecting DUT.
DM 6243 L : 4960 pF (On terminal socket rather than leads)
Old Bridge: 4600 pF approximately. It's a pot with a big perspex pointer on the 1 to 10 scale.
