Alternative req'd for wet tantalum axial caps

[Richie_asg1]

Hi folks,
I'm just sorting out a military radio built around 1970 with a failed PSU. This seems to be a common trend on this model. Problem I'm having is finding a replacement for the caps they've used which are axial 3.6uf 150Vdc wet tantalum with a metal can and red glass seal.
The thing is - a lot has happened since 1970, so is there a better alternative out there now - in this odball size?
The equipment is all sealed up and dry but can get quite hot, and these have lasted 40 years - will modern electrolytics last that long?

Similar types in the HF end - would the alternatives be suitable here as well?

Many thanks to this great forum.
Richie.

[999999999]

Re: Alternative req'd for wet tantalum axial caps

In that size I'd try a film cap. Go with electrolytics only if the capacitance value is high enough that cost or space prohibits using another type. Try to determine if the 3.6uF is a critical frequency/timing value or if something close would work.

If voltage is low enough on the HF end you can use modern dry tantalums or polymer caps... probably axial or radial leaded on something that old. Depends on the specific cap specs needed.

If it doesn't "need" to be all sealed up for your use or purposes you might consider modifying it for more ventilation even if it just means adding some passive cooling holes here and there.

[Richie_asg1]

Re: Alternative req'd for wet tantalum axial caps

Thank you for the quick reply. I have repaired some valve based equipment that had perfectly happy yellow polyester film caps in there so this looks good. The psu in the radio only has to supply 4 voltages from a 24v battery, but one of those is 110v with an inverter. I think it overshoots a bit then is regulated back down to the 110v. Without detail I think the electrolytics are there as smoothing caps on the 110v rail to 0v, and there are some more in the oscillator module just to keep things clean.
Is there any problem with using non polarised capacitors in place of electrolytics to remove ripple from the supply?
I think I'll try and keep to the values in the oscillator circuit if replacements are needed.

Everything is overprotected in this radio and they spent a lot of money making it EMP hardened. Don't really want to cut holes in it as it is water resistant to a metre for 2 hours minimum - I reccon more. It was pressurised when I opened it.

[999999999]

Re: Alternative req'd for wet tantalum axial caps

NP caps can be used for supply ripple w/o problems.

[Richie_asg1]

Re: Alternative req'd for wet tantalum axial caps

Cheers, will try them and see. Can't be worse than dead can it Although they did make use of the small size components, they put them in larger screened units anyway, so should get away with it.

Many thanks.
R.

[999999999]

Re: Alternative req'd for wet tantalum axial caps

Keep in mind that with seals that old, it may not be as water resistant anymore after it's reassembled. Depending on seal type I might coat them with silicone grease, or add some non-permanent, peel-away type gasket sealant.