Philips bypass capacitors in 203U - Specifications? (Techniek Radio/TV)

door Maarten Bakker , Haarlem / Delft, 02.03.2023, 20:47 (631 dagen geleden) @ Robert Lozier

This was the way Philips potted their impregnated paper capacitors from the 1930's on. They were made almost the same way throughout the 1950's and at least part of the 1960's. From the late 1950's on, longlife epoxy coated polyester capacitors took over partially. For high voltage, low loss, high dV/dt applications, Philips continued to use paper or mixed dielectric capacitors, though shifting to metal or plastic casings and epoxy potting over time. Starting in the 1970's, polypropylene capacitors took over for most of the remaining applications, though I think Vishay BC might still have a small series of MKT-P mixed dielectric capacitors for designers who insist on using them but got burned (sometimes literaly) by other brands.

While those tar encapsulated types weren't too bad as far as affordable paper capacitors go (when new they were better than even the few remaining current paper types - think RIFA), they should be considered 'replace on sight' if your goal is to restore an apparatus with the goal of using it daily. If they don't leak electrically at low voltage and room temperature, they will leak at higher voltage or after warming up a bit. A telltale sign is that even when cold, the measured capacity is often much too high.