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 Post subject: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 6:45 pm 
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Location: Northern Minn. 56472
Hello all on the forum.

I am repairing a 9 tube Zenith with a ton of these Black Capacitors and I wonder approximately what years these were made by Sprague? Are they really old enough that I should change all of them out?

G.
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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 7:09 pm 
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50s and 60s molded paper types. I guess they felt they were better sealed than wax types but still can get leaky. Cheap to replace them with something like the yellow mylar types and no further worries. The worst molded black caps like that I have seen are the bumblebees, they are always leaky and often value changed from markings. I have some molded caps marked "black cat" and they are unused. I tested them anyway and they all were good for leakage/value at the time. But I have not used them.


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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 7:10 pm 
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Joined: Aug Tue 24, 2010 8:56 pm
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Location: Northeast Florida
Some capacitors in cases like those are paper, and some are mylar. It's very hard to tell sometimes, and so my rule of thumb is to replace them anyways---better to err on the side of caution.

As far as age goes---if it's a paper capacitor (and I'm pretty sure it is), it's absolutely time to change them. Paper caps in plastic cases fared no better than the standard wax type. In fact, I think they're actually worse---when a wax/paper cap fails, it will blow out the end, when a paper/plastic cap fails, they tend to explode into shrapnel.

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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 7:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Rochester NY USA
The yellow labeled ones are the same as the striped ones ("bumblebees") - they're pretty much all bad. Red labeled ones are "difilm" - paper/Mylar and usually are good - I've yet to find a leaky one.


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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 8:43 pm 
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Joined: Sep Tue 15, 2015 1:16 am
Posts: 263
Location: 18424 PA
wazz wrote:
50s and 60s molded paper types. I guess they felt they were better sealed than wax types but still can get leaky. Cheap to replace them with something like the yellow mylar types and no further worries. The worst molded black caps like that I have seen are the bumblebees, they are always leaky and often value changed from markings. I have some molded caps marked "black cat" and they are unused. I tested them anyway and they all were good for leakage/value at the time. But I have not used them.


Ebay fodder. certain values were used in older guitars and command a good price. Those blue molded ones also, used in Fender amps.


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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Fri 09, 2018 9:08 pm 
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Joined: Oct Sun 05, 2008 7:39 pm
Posts: 669
Location: Northern Minn. 56472
Okay, thanks everyone. I have just started changing them out and so I'll continue to get rid of all of them.

This Zenith is from 1938, so maybe someone did some work on it in the 50's and put those black caps in there.

\ G.


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 Post subject: Re: Sprague Black Plastic Capacitors
PostPosted: Nov Sat 10, 2018 5:09 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4332
Location: Charleston, W.Va.
Hi philconerd,
+1 to your plan to replace these caps.

Those yellow-lettered black plastic-bodied Sprague caps are in fact paper caps and should definitely be replaced. Likewise for any from the same era which have white lettering. On the other hand, were these Sprague caps to have had red/orange lettering they would be mylar-film caps dating from the late 50's or newer, and would almost certainly still be good.

You can be sure that if these are in your 1938 Zenith radio then they were later replacements and, as you surmise, probably date from service work done during the 1950's or possibly as late as the 1960's. But if the workmanship is good don't fault the radio repairman who put them in; he was probably using the capacitors which he felt were the best available to him at that time.

On a side note, I don't know the exact model of your 1938 Zenith radio. But I always enjoy the rare cases when I see a pre-WWII radio which exhibits quality service work done as late as the 1950's or 1960's. This usually means that the person who originally owned the radio valued it and tried to keep it in good operating condition for a great many years.

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