Old Mustard caps possible problem ..... have a look!!

5F6-A

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3,030
Hello. I have a stash of never used 60s and 70s mullard mustard caps. Some made in England and some made in Spain (labelled Bianchi) to the same specs. i have noticed that the cement has cracked slightly on some of them. They test absolutely perfect but I wonder if I should use them in amps. I think it's just a aesthetic issue with components that are 50 years old. I guess I could patch them up with a tiny bit of epoxy to stop the crack from getting larger. What do you think?


 
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Cracks are good, it means they're genuine.
The original mylar film has gone soft ( off ), and where that epoxy/paint joins the mylar, the mylar is actually tearing off, what you're seeing is paint/ epoxy with the very ends of the rolled up mylar sheet juuust attached to the paint/epoxy. So what you have going on there is sort of like taking a bite of the end of a rolled up newspaper.
I've pulled these cracked caps apart by folding up on the leads and examined the now broken off ends carefully.
In storage, the leads have been bent a little ,it's that leverage that has pulled the end out and cracked the rolled up mylar.
These cracks have no effect on the sound of the capacitor, what you do is get 5 minute epoxy, clear stuff, mix it up and swivel the cap with one of the leads while carefully holding the blob of epoxy, now on the end of say, a screwdrivers flate blade..you just want to coat the cracks, I coat it on thick.
Carefully put the cap down somewhere where the epoxy doesn't get wiped off, let dry, and then use as normal.
 
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they lay a sheet of foil down, then a sheet of mylar over the top, then roll it up into a cylinder, attach the ends of the foil to each end lead, and then coat them in that mustard colored epoxy. I've stated the mylar is soft, but I should also add that if you peeled that end off, you would also find the very ends of the foil stuck to the epoxy cap, it looks like metallic dust. Foil is already soft stuff, it's the Mylar film that had most of the strength, now, that strength is gone because the Mylar has gone off, it's super soft, if you unroll one of these, the mylar falls away in your hands, its just like a plastic shopping bag that disintegrates over time.
 

5F6-A

Member
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3,030
Excellent news! Apart from this little niggle, these caps seem great. I can see why they were so successful. Not only they sound great but electrically they behave impeccably.

BTW, I have others (see photo below). These are impeccable. Can you tell if they are fake? (hopefully not)

 

EdFarmer

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878
I'm not certain about electronics manufacturing but I believe that Bianchi is Italian, not Spanish . . .
 

5F6-A

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3,030
I'm not certain about electronics manufacturing but I believe that Bianchi is Italian, not Spanish . . .
Philips decided to call their mustard caps for the Spanish marked Bianchi (for whatever reason). They were made in the very beautiful Basque Country region of northern Spain prob in very early 70s. These caps were made in Spain for the Spanish consumer (laws used to protect home made products) but otherwise identical to the Mullard. Probably the best polyester cap for audio ever made.
 

EdFarmer

Member
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878
Philips decided to call their mustard caps for the Spanish marked Bianchi
Interesting . . . I'm surprised that the Italian company let that happen. They had a presence all over Europe at the time.

Thanks for the correction!
 

pulse.

Gold Supporting Member
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2,317
Is there any audible differences between Mullard mustards and Bianchi mustards?
 

gldtp99

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3,828
Old film caps that are falling apart ?

I don't care if they are "Real Mustards"

I'm not going to use them to build an amp

Come on---- they're old and falling apart

Part of their function is to block Hi DC Voltage and the outer material is so old and degraded that it's falling apart ?

This doesn't sound like a safe condition to me

I'm going to use a new film cap

Such as:

Axial 0.022 uF 630 VDC Film Capacitors – Mouser

I'd probably use the M150's since I have plenty on hand and no need to order any

I build my amps with safety and long trouble-free life in mind

I won't use old, falling apart components

Even if they are "Real Mustards"
 
Last edited:

jvin248

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5,460
.

Sure, those old parts are fun to look at and admire ... but not in an amp you want to use and not destroy.


.
 

gldtp99

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3,828
But what about MOJO??????
:eek: :eek: :eek:
I get the "cool factor" surrounding some old, out-of-production components

I just pulled/examined some old Sprauge Black Cat film caps out of an old PA head for possible use in a 20-25 watt Plexi I'm in the process of building

These Black Cats look good -- no cracks, have long leads ---- but the .047uF's tested high .062-.068uF on my Fluke so I won't use them

I have plenty of new film caps of many different brands on hand

These caps will be subject to heating/cooling cycles, vibration, etc and I need the ones I end up using to function properly/safely for a long period of time

So old caps that are badly drifted (or cracked and in danger of falling apart inside the amp) are out of the question

I think any other approach would be irresponsible and maybe even criminal

Maybe I'll use Xicon MPP's

Maybe something else, I haven't decided yet
 

J M Fahey

Member
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2,371
subject to heating/cooling cycles, vibration, etc
THAT is an important point,which overshadows lesser or even imagined ones such as Mojo or appearance.

Personally don´t much believe the "plastics inside getting mushy" theory, not much cause for degrading in the dark, isolated from atmosphere inside a hermetic epoxy cover, instead just think that innards are somewhat elastic simply by construction technique, not a solid chunk of any material but a tightly wrapped pack of interlaced foils, any outside pressure can innards slightly flex and crack *thin* rigid epoxy, period.

I bet the bag holding those caps was crushed or at least subject to pressure some time in the last 40 years.
 




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