Ive also heard it said that any electrolytic with a rating of 500 volts or above is to be suspected.
Typically the good modern brand caps only go to 450 volts , thats a bit marginal in a 50W Marshall which has around 420volts at the plate . The 100W Marshall has even higher plate voltages but they use two caps in series with voltage dividing resistors to balance the drop equally .
I guess it might be possible to re-stuff the old 2x50uf 500v capacitor housing with four modern 100uf 250 volt units and some balancing resistors , to make a proper 2x50uf @500volts , still a lot of crap and mess involved over a straight swap , even if the resulting composite cap was better .
Typically the good modern brand caps only go to 450 volts , thats a bit marginal in a 50W Marshall which has around 420volts at the plate . The 100W Marshall has even higher plate voltages but they use two caps in series with voltage dividing resistors to balance the drop equally .
I guess it might be possible to re-stuff the old 2x50uf 500v capacitor housing with four modern 100uf 250 volt units and some balancing resistors , to make a proper 2x50uf @500volts , still a lot of crap and mess involved over a straight swap , even if the resulting composite cap was better .
