Vintage Synth Repair

my understanding of the use of tants & cans in circuits was this: 

electrolytics are cheap & good in situations where you need a big
"bucket" for charge, such as 50/60Hz filtering in power supplies, but
they are pretty rubbish at high frequencies, reverse leakage & being
anywhere remotely near their stated value in uF, which can also vary
with temperature & humidity. that said, they tend to last quite a long
time before giving up the game rather spectacularly. they'd be the
first thing to change in an old power amp, for instance, or anything
with a linear (big trafo) power supply. their use in cheap audio
circuits inadvertently led to enormous differences in the performance
of otherwise identical devices, such as fuzz-boxes, which in turn has
affected the market for 2nd hand electronica almost as much as the
various kinds of utility op-amp (741, 5532) used in the same devices.

tantalums tend to crop up more where space is limited, where audio
performance is more important (i.e. the reverse voltage across the
device is likely to be equal to the forward voltage), & where the
value has to be within an order of magnitude of the circuit design's
specification. they tend to go short if they fail. this is especially
troublesome as so many of them are used in linear power supplies
(often adjacent to & in parallel with much larger electrolytics) for
noise-reduction, & especially when the power supply is for audio,
control or video purposes. they have been responsible for the abrupt
end of many series regulator devices (78xx, 79xx).
if they don't fail within six months, they tend to last as long as
their rolled-up-paper cousins, but with less variation in their
performance or capacitance.

I'd replace like with like, every time. 
especially in the early 70s, people didn't use tants just for the heck
of it or because they were smaller; they were an expensive alternative
then & tend to appear where they are the only suitable option.

duncan.