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 Post subject: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 12:47 am 
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I always replace the wax caps without measurement but I found these in a Philco 37-610 which had been serviced some time ago. I measured every Mallory in the set and the insulation resistance was infinite. The plastic Sprague in view was leaky. Should I leave the Mallory parts in the set? (I did wipe off the dust.)

Thank you,


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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 1:06 am 
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Yes. For the Spragues, if the writing on them is yellow, they are paper caps. If the writing is red, they are bi-film or poly, both of which are usually OK.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 1:35 am 
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Thanks Tom, I am glad I asked. How old do you think the Mallory caps are? They are marked "GEM 6115."

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 2:00 am 
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I don't know exactly. I would think they are between about 1962 and 1975.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 3:17 am 
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Hi Dale,
+1 to Tom's comments about the plastic-bodied Sprague caps. As he says, those with yellow (and sometimes white) markings are paper, and should be replaced. Those with red (or orange) markings are "mylar" film and will almost always still be OK.

In regard to those two Mallory plastic-bodied caps, I am not so sure. It would take someone with more knowledge than I have to tell you exactly what they are inside. Personally, I would either test them for leakage at full rated voltage on an appropriate bridge-type cap tester such as a Sprague TO-series Tel-Ohmike, or if this is not possible or practical I would go ahead and replace them.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 4:38 am 
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Poston,
See my OP. I measured the insulation resistance on a TO-5. Leakage measurements are for electrolytics.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 4:47 am 
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Those brown-bodied Mallory caps are almost certain to be foil/film types, probably from the 1970s. My guess is that they are probably still fine, maybe better than many of the common metalized film caps available today. However, if you really want to test them, leakage may not be a reliable indicator. Plastic film doesn't develop leakage unless moisture has gotten between the layers through a defective case. Otherwise they will test near infinite resistance, or they will test near shorted if there was a puncture that didn't "heal."

What does go wrong with old film caps is the same thing that goes wrong with all plastics eventually: chemical changes in the material that cause it to yellow, lose flexibility, or shrink. Such changes will also cause its electrical dissipation to increase, and this can affect the operation of some circuits. Unfortunately, most eye tube capacitor bridges and handheld digital capacitance meters are not set up to measure dissipation in small non-electrolytic capacitors. It takes an RF bridge, capacitance meter, Q meter, grid dip oscillator, or the like to determine if there is high dissipation in such caps. It can be done with a scope or RF voltmeter, signal generator, non-inductive load resistor, and scientific calculator if one wants to go to the trouble.

But you probably don't.

If the caps are not shorted, low resistance (or leaky) when tested at voltage, I'd go ahead and use them. If the radio circuits perform correctly, their dissipation probably has not reached the point where it is a problem. It is to be noted that the original paper caps had several times the dissipation of new mylar (polyester) film, and about 100 times the dissipation of new polypropylene film, so even if the film has degraded a bit, the radio should still work fine. It's more of a concern where film caps are operated 24/7 in high temperature, high energy environments with lots of ozone.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 01, 2017 5:20 am 
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Mallory GEM Series capacitors are "Molded tubular paper capacitors sealed against moisture with epoxy resin and molded Bakelite." This from Radio Supply Catalog 1964. Strange the GEM 6115 number is for 600V .015. Markings wrong? I have a couple older Mallory Catalogs and will check them if this series are same.
Bill J.


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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Mon 02, 2017 5:36 pm 
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radiodale1 wrote:
Poston,
See my OP. I measured the insulation resistance on a TO-5. Leakage measurements are for electrolytics.

Dale,
I also use a Sprague Tel-Ohmike, in my case a TO-4. And yes, you are entirely correct that when we test electrostatic caps (film, paper, mica, ceramic, etc.) it is for insulation resistance (measured in megohms). And leakage current (measured in ma) applies to electrolytic caps.

I (and others) tend to use the term "leakage" very loosely when describing performance of all capacitors. In the future I suppose I should be more particular in my terminology 8) .

But in any case, if I was measuring infinite insulation resistance on those Mallory molded caps via a TO-5, then I would certainly leave them alone. As Chris108 says, they may be better than many of the common metalized film caps available today.


Chris108,
Thanks very much for your excellent summary of performance of film-foil caps VS. paper caps. You have also made more lengthy comments on this before in prior posts, which should be required reading for anyone replacing paper caps in a high-quality receiver.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Mon 02, 2017 6:17 pm 
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They are paper,I would replace them.


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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Mon 02, 2017 6:31 pm 
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If in doubt, replace. Caps are cheap.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Mon 02, 2017 6:52 pm 
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Lou deGonzague wrote:
They are paper,I would replace them.

Hi Lou,
Yes, if they are indeed paper. But they might also be foil/film (if so, most likely mylar). So the real question here, and the one originally asked by Dale is: Exactly what are these Mallory molded caps? As best as I can tell, no one here has yet been able to positively identify them. Probably because there are no visible OEM part- or series- numbers visible in the original photo.

EDIT: I am wrong, I just re-read this entire thread, including the post by Bill J. where he identifies the Mallory GEM Series capacitors as "Molded tubular paper capacitors".
So considering that they are showing infinite insulation resistance after testing on Dale's TO-5, the question of whether or not to replace them now becomes a judgement call.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Mon 02, 2017 7:48 pm 
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They are listed in my Allied 1960 catalog, Mallory GEM molded tubular paper capacitors. Your 6115 is listed, was 18 cents back then. I happen to have a few of these NOS .1 and .005 600v and I tested them on my Sencore LC-53. Values were very close and nary a micoamp of leakage at 600v :shock:


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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Tue 03, 2017 6:15 pm 
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Lou deGonzague wrote:
They are listed in my Allied 1960 catalog, Mallory GEM molded tubular paper capacitors. Your 6115 is listed, was 18 cents back then. I happen to have a few of these NOS .1 and .005 600v and I tested them on my Sencore LC-53. Values were very close and nary a micoamp of leakage at 600v :shock:


Yeah, they are in my 1960 Radio-Electronics Master as well, but no mention in the 1963 edition.....

Pixellany nailed it, with no discussion needed - caps are cheap - replace with another modern one and done...

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Tue 03, 2017 7:23 pm 
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If it's your own set, you could always leave them in as a test or an experiment to see how they will last. Mallory made decent caps so they could be OK for a while yet, but being paper indicates that they will eventually fail.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sat 07, 2017 3:46 am 
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Those look like rebranded Good-All "Dart" Mylar capacitors from the 1960s or early 1970s, and they are probably OK. Zenith used them heavily during that time, with their own part numbers added.

The original Mallory "Gem" caps from the 1950s had squared-off bodies, and were a very dark red color with black printing; every one of those that I have tested was leaky.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 08, 2017 1:01 am 
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That makes more sense. I thought I recalled seeing this type of cap on equipment newer than the early 1960s, and also confirming low leakage on some that I have come across.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Sun 08, 2017 3:43 pm 
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One way to find out, replace one of them with a modern component, then break open the old Mallory to see what they dielectric is and post here for future reference.

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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Tue 10, 2017 3:52 pm 
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Seems to me unlikely Mallory would need to be selling rebranded caps. Here is a shot of both types and the part numbers are consistent with the 1960 Allied cat. both show no leakage on the Sencore LC-53.
Image


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 Post subject: Re: Mallory Film Caps Reliable?
PostPosted: Jan Tue 10, 2017 6:12 pm 
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Neither of those looks quite the same as the picture at the top of the thread, which I recognize as a very common type of cap from TVs, perhaps as late as the 1970s.

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