GRC-106 Military radio repair. Source odd capacitor?

[TerraHertz]

The thread title should be "Starting to attempt to..." but we'll see.
The first problem I've hit is a dead cap, surprise surprise. But it's an unusual form factor and type.
See http://everist.org/NobLog/20160421_antique_mil_radio.htm  and pics below.

It's a wound tantalum foil capacitor, 8uF 250V
Cylindrical, axial leads. Length of the body is 55mm, diameter 10mm.

Has anyone any idea where I'd buy something like that, even if only in format?
There's no room for anything fatter. Not to mention the clip it's supposed to fit in.

[mmagin]

Impressive that it hasn't blown into orbit!
My inclination would be to just try a suitable axial aluminum electrolytic.  I guess due to the chokes the ripple current shouldn't be too bad.

[SeanB]

Sorry Guy, but that is going to be pretty much an unobtanium device. Good though it is polarised, so a regular 10uF 250V radial electrolytic will fit nicely in that clip, and then you only have to extend the leads with some nice sleeving to match the holes. See the other 2 with rubber bungs next to it, change them as well. The glass sealed ones ( C5) will last forever, or at least they will outlive the rest of the unit.

The colour change is an indication of the oxide layer thickness, and the missing electrolyte is a lovely sulphuric acid blend, to keep the oxide film stable.

At least the 390n units are easy to get as 400V rated parts now, and will do nicely there space wise.

ps you have a parcel winging it's way to you.... Even has a note inside for you to enjoy.

Edit: What do you know, RS has the perfect replacement, even fits the clip and looks like the original as well..

http://za.rs-online.com/web/p/aluminium-capacitors/2267081/

RS 226-7081 10uF 200V axial cap, 105C rated as well. ESR is good enough ( 10R) and lifetime at 105C is a year. Keep it cooler and it will do better though.

[Ian.M]

Mouser have a 200V 8.2uF 9.5mm dia axial electrolytic that should be suitable.
http://eu.mouser.com/ProductDetail/Vishay/30D825M200DC2A

[edpalmer42]

Google for 8uf 250v tantalum .  First hit!  No problem!  Well......maybe you should be sitting down when you check the price! 

http://www.tedss.com/CL35BS080LP3

Ed

[SeanB]

Google for 8uf 250v tantalum .  First hit!  No problem!  Well......maybe you should be sitting down when you check the price! 

http://www.tedss.com/CL35BS080LP3

Ed

Still a cheap one, try looking at Vishay's larger value units. They go up to 12 000uF  but you might not like the price..

http://www.vishay.com/docs/40141/dscc1001.pdf

[TerraHertz]

Thanks for all the help everyone.
Doh. I wrote that up late at night, and I guess being tired makes my brain revert to pre-internet habits. Of forgetting to search first, speak after.

Google for 8uf 250v tantalum .  First hit!  No problem!  Well......maybe you should be sitting down when you check the price! 
http://www.tedss.com/CL35BS080LP3

Oh my god.
I don't think I'll be using those. Any parts I buy for this unit should be bought in min. qty 20. For uh, reasons.

Mouser have a 200V 8.2uF 9.5mm dia axial electrolytic that should be suitable.
http://eu.mouser.com/ProductDetail/Vishay/30D825M200DC2A

Thanks, in the sense that I'm reassured the form factor exists. But the order details are awkward.
Non-stocked, 13 weeks, min qty 510, Au$2.24 ea by 510...  This is actually worse than the tedss ones.
Next stop: Aliexpress.

Edit: @SeanB  (PM'd you too)
Ah, that works. http://au.rs-online.com/web/p/aluminium-capacitors/2267081/
Au$9.51 each, next working day. So that's solved for this unit.
Still going to check Aliexpress for qty buy.


Meanwhile, I wonder what thin tantalum film is useful for, besides capacitors?

[Ian.M]

It can be used as a getter in a vacuum tube.  It might also be of interest to a chemist . . . .

[SeanB]

If you are doing DIY vacuum tubes it can make feedthroughs as it adheres to glass.

[BMack]

Are you planning on changing those other caps? I would recommend it.

[TerraHertz]

Are you planning on changing those other caps? I would recommend it.

The other tubular tantalums?
Hmm, my objective is to get it working in-spec for sale, and also to maintain as much historical accuracy as possible. There are a lot of other modules (and the amplifier unit) to go through yet. I think I'm going to be fairly strict about only changing parts that actually show sign of failure. And those ones, under a magnifier, look fine. At most I'll lift one end and measure to check they are in tolerance. I'm poor too, and just two of the 10uF 200V caps cost $20. (Won't get them till Tuesday.)

A very old radio like this can be expected to need maintenance. Plus, it seems they tend to be bought by collectors who have many different military radios, and don't use any particular one all that often.
I have a few more to do too, now and then after this one. So when I do replace something I also have to order a quantity from aliexpress or wherever I can get cheap but slow.

[dacman]

If a 10 uF will do, then:

http://www.newark.com/multicomp/mchv100m2eb-1021-rh/aluminum-electrolytic-capacitor/dp/79K3632

http://www.newark.com/multicomp/mctea100m2eb-1021p/aluminum-electrolytic-capacitor/dp/79R7579

http://www.newark.com/illinois-capacitor/106tta250m/aluminum-electrolytic-capacitor/dp/30K6597

[TerraHertz]

If a 10 uF will do, then:

http://www.newark.com/multicomp/mchv100m2eb-1021-rh/aluminum-electrolytic-capacitor/dp/79K3632

http://www.newark.com/multicomp/mctea100m2eb-1021p/aluminum-electrolytic-capacitor/dp/79R7579

http://www.newark.com/illinois-capacitor/106tta250m/aluminum-electrolytic-capacitor/dp/30K6597

Cool, those prices are more reasonable. Still to see what they work out as with postage to Australia.
For comparison, the same as your third one, but from Element14 Australia:
  http://au.element14.com/illinois-capacitor/106tta250m/aluminum-electrolytic-capacitor/dp/9680730?ost=MCHV100M2EB-1021-RH&selectedCategoryId=&categoryNameResp=All%2BCategories

[BMack]

Are you planning on changing those other caps? I would recommend it.

The other tubular tantalums?
Hmm, my objective is to get it working in-spec for sale, and also to maintain as much historical accuracy as possible. There are a lot of other modules (and the amplifier unit) to go through yet. I think I'm going to be fairly strict about only changing parts that actually show sign of failure. And those ones, under a magnifier, look fine. At most I'll lift one end and measure to check they are in tolerance. I'm poor too, and just two of the 10uF 200V caps cost $20. (Won't get them till Tuesday.)

A very old radio like this can be expected to need maintenance. Plus, it seems they tend to be bought by collectors who have many different military radios, and don't use any particular one all that often.
I have a few more to do too, now and then after this one. So when I do replace something I also have to order a quantity from aliexpress or wherever I can get cheap but slow.

Yes. I've found these to often be the cause of many a pain in the butt issues. They seem to drift out of spec but show no outward signs of failure. If you have any issues after you finish you may want to revisit some of these tantalums. Before you get there you might want to look them over with some good magnification, sometimes they pop but it's hard to see because of the casing. As recently as about two months ago I had a Tanberg 10XD reel to reel that had intermittent distortion in one channel, turned out to be one of the tantalum caps.

[acbern]

One thing to consider is that maybe for AC reasons a tantalum capacitor was used instead of a normal electrolytic one. Therefore, and unless otherwise proven by reviewing the design, it may make more sense to use a foil capacitor. May be difficult to find a matching one given space available but should be doable (maybe spilt into two).

[amyk]

Google for 8uf 250v tantalum .  First hit!  No problem!  Well......maybe you should be sitting down when you check the price! 

http://www.tedss.com/CL35BS080LP3

Ed

Still a cheap one, try looking at Vishay's larger value units. They go up to 12 000uF  but you might not like the price..

http://www.vishay.com/docs/40141/dscc1001.pdf

http://www.mouser.com/ProductDetail/Vishay/HE3C243M050BZSS/

[MarkL]

Surplus Sales of Nebraska has a good collection of old parts, especially for old radios and transmitters that are impossible to find elsewhere.  Take a look here:

  http://www.surplussales.com/Capacitors/Electrolytics/4uF-119uF.html

They don't have an exact replacement, but if you still want tantalum there are a couple of ones that are close.  And if you don't mind paralleling two of them, there's (CFE) 000005R00ADE which is 5uF @ 250V for US$3.50 ea.

[mmagin]

One thing to consider is that maybe for AC reasons a tantalum capacitor was used instead of a normal electrolytic one. Therefore, and unless otherwise proven by reviewing the design, it may make more sense to use a foil capacitor. May be difficult to find a matching one given space available but should be doable (maybe spilt into two).

Looking at OP's linked article, it looks like the capacitor is at the output of a switching supply, so you do want it to tolerate decent ripple current, but there's already 2 series L and 1 C before it after the bridge rectifier, so my hunch was that an ordinary name-brand electrolytic can probably handle this duty.  And with electrolytics or tantalums, I think it makes sense to prefer new to new-old-stock.

[Ian.M]

I would avoid NOS from the same era - especially same brand, as they are likely to be at high risk of similar age related can or seal failures.

If appearance and retention of original parts were priorities, one could stuff an array of SMD ceramic caps on a thin double sided PCB inside the original can, which would also significantly reduce ESR and thus ripple. Unfortunately  the O.P's deconstruction of it was done without any consideration for such conservation methods.