Many of these aged caps lose their capacitance due to their age & it's always best to desolder them and measure them prior to powering them up.
Some caps even gain capacitance!
The yellow microbee filter caps predate the introduction of pressure minimisation creases hence the cracking at the base and it not blowing its top.
These days the estimated longevity of capacitors can be calculated from their thermal and lifetime specifications.
The higher the spec the higher the price!
e.g. 12000Hrs@105C, 2000Hrs@85C
Generally, the hotter they're run the shorter their lifespan.
The giant S-100 Bus power supplies filter caps which are about the size of small drink cans are damned expensive so to prevent these exploding reformed them.
This is quite easily done with a laboratory power supply that has both voltage and current limiting controls and a suitably sized bleed resistors or programmable DC Load.
It's also recommended to measure the open circuit output voltage from the transformer. The transformers sold at Applied Technology had relatively high open circuit and loaded voltages relative to their specified voltages.
e.g. 16V output often measured up to 25V open circuit and 20V under load.
The higher output voltage means that the downstream regulators run hotter to dissipate the unneeded power.
One also needs to ensure that the accompanying components such as filter caps are sufficiently rated.
Some caps even gain capacitance!
The yellow microbee filter caps predate the introduction of pressure minimisation creases hence the cracking at the base and it not blowing its top.
These days the estimated longevity of capacitors can be calculated from their thermal and lifetime specifications.
The higher the spec the higher the price!
e.g. 12000Hrs@105C, 2000Hrs@85C
Generally, the hotter they're run the shorter their lifespan.
The giant S-100 Bus power supplies filter caps which are about the size of small drink cans are damned expensive so to prevent these exploding reformed them.
This is quite easily done with a laboratory power supply that has both voltage and current limiting controls and a suitably sized bleed resistors or programmable DC Load.
It's also recommended to measure the open circuit output voltage from the transformer. The transformers sold at Applied Technology had relatively high open circuit and loaded voltages relative to their specified voltages.
e.g. 16V output often measured up to 25V open circuit and 20V under load.
The higher output voltage means that the downstream regulators run hotter to dissipate the unneeded power.
One also needs to ensure that the accompanying components such as filter caps are sufficiently rated.