Re: Replacement for Tantalum cap in 7603


tinkera123
 

On Tue, Apr 17, 2018 at 08:13 pm, Chuck Harris wrote:


You are kind of stuck on the high voltage Tantalum caps.
You have a couple of choices. First, is you can simply
replace the part with an identical spec'd capacitor, and
run the risk that it will only last another 30-40 years.

Modern parts seem to be much better than older parts.

Or, you can replace it with an aluminum electrolytic
capacitor of similar voltage, and about double the
capacitance... and run the risk that it will only last
another 30-40 years.

Either is a fine solution.

There is one case where you might not want to do this, and
that is the case of the wet slug tantalum capacitor. They
tend to be used when a small capacitor with a voltage as
high as 150V is needed.

Sometimes, you actually need for a capacitor to be low
leakage, and dry and wet slug tantalum caps are low leakage.
In those cases, you pretty much have to either bite the bullet,
and buy the expensive capacitor.... or, if you have enough
room, replace it with a usually physically larger film cap.

I really wouldn't recommend using tantalum, or electrolytic
capacitors in series, unless the circuit can support the use
of a resistor divider, in parallel with the capacitors, to
divide up the voltage between the capacitors.

Tantalums cannot take a joke. If they get over voltaged,
or worse still reverse biased, they will die.

-Chuck Harris

tinkera123 wrote:
Recently, the C492 Tantalum cap on the Vertical Amp board failed in my 7603
scope .... documented in an earlier Thread. I am up and running again with an
1uF 100v aluminium electro cap ... but the Forum 'general opinion' seems to
prefer a higher voltage Tantalum replacement.

I have been looking at the Mouser et al sites and Tantalums over 50volt are
expensive or non-existent .... and more so in Australia.

If I don't find a 1 or 2uF 100v 105deg Tantalum cap ... I could use 2 x 2uF
50v 105deg Tantalum caps (or larger uF) in series.

Is this a reasonable solution? ..... or do 'in series Tantalum caps'
create problems eg less effective? noisy??

Cheers,
Ian
Thanks Chuck and Ed,
30 to 40 years is long enough for me. In goes another Tantalum 1uF 50v 105 deg. ... :)
Ian
PS Have I responded correctly?? Clicked "Reply" under Chuck's response .... then "Full Quote" icon .....
Do I have to do the same for Ed??

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