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 Post subject: New capacitor values
PostPosted: Aug Sun 22, 2021 4:44 am 
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Joined: Feb Fri 07, 2020 12:57 am
Posts: 105
Location: Kelowna BC, Canada
I bought new caps for the first time for general radio re-capping from a commercial seller. As I was re-capping I decided to check the values of the old caps vs the new ones on my TCI tester...and was surprised to see that the old ones always tested closer to the stated value. For example...
5000pf old: 5600 new:3825
500pf. old: 512 new: 400
0.1uf old: 0.1 new: 0.082
0.01uf old: 0.011 new: 0.008
0.05uf. old: 0.05 new: 0.041

These are new yellow film caps from a seller that probably sells to many of you...are they close enough for tube radios? How close should I expect them to be? Assuming the numbers are accurate, would 0.082uf in place of a 0.1uf make a practical difference in a late 50's German tube set? It seems to sound ok in operation.

No telling really how accurate my meter is but the old ones seem remarkably close to spec. Thanks all.


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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 5:33 am 
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Keep in mind that American consumer radios generally have a 15% plus or minus tolerance for parts.

Assuming German sets are the same, you should be fine with "close enough". That and of course modern values are somewhat different.

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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 1:38 pm 
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I have found similar results. I don't like using the yellow caps and instead buy Panasonic capacitors from Newark or Digikey.

Cornell Dubilier make yellow capacitors and I don't believe the ones you have referred too are made by them?


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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 3:24 pm 
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Joined: Feb Wed 07, 2018 6:52 pm
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Location: Stone Mountain, GA
I'd suspect your meter. Simplistic ones will treat leakage as additional capacitance.

Since all the new read low, sounds like your meter is not accurate.

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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 6:59 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island NY
German radio companies and their parts suppliers prided themselves on precision. Wouldn't surprise me if the original caps were 10% parts or possibly better. The fact that so many of them come in on spec says to me that your meter is probably fine. Leakage or high ESR in capacitors usually makes them read higher than they are on digital C meters, not lower. It just looks to me like the replacements are in the 20% tolerance class and you got one that is slightly beyond that.

Where did the new caps come from? If they are typical unbranded polyester "yellow jackets" then there's your answer. Such caps are often made by small garage operations in China that also make plastic umbrellas and things like that. There is no QC of incoming materials nor final test of finished product; they simply have the winding machines set up to produce capacitors of a physical size which gives approximately the correct capacitance. Selling factory rejects from the bigger companies is another common practice. They work (usually) and are close enough in value for most purposes. You can get caps that are close to, or exactly on value if you want, but of course you'll pay more.

Usually in engineering things are not designed to fail at the exact point where tolerance is reached. They are usually designed to keep working until things are well past that. Obviously the radio still works with 20% caps in it, and that 3850 pF which was originally 5000 pF is 25% low. But my guess is that if you were to put it on a test bench and really measure its performance: sensitivity, signal to noise, selectivity, the whole nine yards, you'd probably find that it is not performing as well as it did when it was new. The other thing is, it may be on the edge now where any aging or deterioration in the caps will take it beyond the point of no return and it will stop working.

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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 7:43 pm 
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Joined: Feb Fri 07, 2020 12:57 am
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Location: Kelowna BC, Canada
Thanks for the replies everyone. I will refrain from mentioning the supplier’s name but it is a vendor advertising on the forum…I assumed this their products would be well vetted by the group here so I hope it’s a case of close-enough or my meter testing a bit off.

I enjoy the radio for casual listening enjoyment… and who am I kidding, the odd repair is fun as well…so the fact that my 1958 technology may not be at optimal efficiency is not a concern, even if it is probably true. I might try an alternate supplier next time just to compare the results. All the resistors I bought from the supplier test very close to rated value…just a bit off on the caps, including some metal polypropylene orange-brown dipped.


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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 7:59 pm 
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We don't typically change electrolytics because the value is off---rather because the dieletric layer goes bad---giving you a cap that goes BOOM!!!
Just about any brand of electrolytic is OK---Many of us get them from JustRadios or Sals.

Thr only electrolytic that ever went bad here was a Nichicon from Mouser.....

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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 8:11 pm 
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Before passing judgment on either the old or new caps, I would want to confirm the accuracy of yours, or any other capacitor meter, used for the testing.

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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 9:58 pm 
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Joined: Feb Fri 07, 2020 12:57 am
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Location: Kelowna BC, Canada
Agreed that my meter is unknown and could easily be giving erroneous readings. It struck me that the caps I removed all tested very close to what is called for and the replacements are all testing further off and that’s what caused me to ask the question.

Radio works great, 60 year old electrolytics/general caps are replaced (diode bridge is waiting to replace selenium rectifier)….I really have no complaints.


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 Post subject: Re: New capacitor values
PostPosted: Aug Sun 22, 2021 10:13 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island NY
The German chemical industry basically started with plastic film caps in the mid 1950s. Polycarbonate and polystyrene were among the first films used, going back to about 1955. By 1958-59 when your radio was made, polyester (Mylar) was available. So it is quite possible the caps you replaced were plastic films, and if so I'd expect them to be pretty darn close to spec for capacitance. It is possible they had other problems like cracked outer coatings, low leakage resistance, or high dissipation that made replacement worthwhile, but unless those defects are really severe, they do not change the capacitance value.

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 Post subject: Re: New capacitor values
PostPosted: Aug Mon 23, 2021 12:23 am 
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Joined: Feb Wed 07, 2018 6:52 pm
Posts: 1125
Location: Stone Mountain, GA
Guzzifan wrote:
These are new yellow film caps from a seller that probably sells to many of you...are they close enough for tube radios? How close should I expect them to be? Assuming the numbers are accurate, would 0.082uf in place of a 0.1uf make a practical difference in a late 50's German tube set? It seems to sound ok in operation.


Just received a bunch of the "yellow caps"

Here's one tested on my DE-5000 LCR meter:
Attachment:
yellowcap.jpg
yellowcap.jpg [ 462.14 KiB | Viewed 725 times ]


0.1uf reads 0.09853uf, just under 1.5% low. Probably within the tolerance of the meter itself.

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 Post subject: Re: New capacitor values
PostPosted: Aug Mon 23, 2021 7:56 am 
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Joined: Jun Sat 09, 2007 8:14 am
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Location: Melbourne, Florida
I just spot checked about 10 different values of my yellow ones and all were within 2% or so, some a little high, some a little low. Tube radios seldom had anything better than 10% for any component.

RRM


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 Post subject: Re: New capacitor values
PostPosted: Aug Mon 23, 2021 1:01 pm 
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Location: Annapolis, MD
Keep in mind that---if a cap (or any other part) is speced at something like 5, the widget might work justfine if the actual value were in the range of---eg---4 to 6.

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"Voltage is fun to watch, but it's the CURRENT that does the work."


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 Post subject: Re: New capacitor values
PostPosted: Aug Tue 24, 2021 3:40 pm 
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Joined: Jul Sun 09, 2006 3:11 am
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Location: Clearwater, KS
I spot check new caps I buy. The yellow caps are always well within 10% spec, many 1-2%. I bought a bunch of cheapo brown drop radials from an eBay seller that were awful. Some were 40% off.


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 Post subject: Re: New capacitor values
PostPosted: Aug Tue 24, 2021 10:09 pm 
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I've had good luck with the caps I buy from Sal. I had one instance where a new yellow was bad, so that taught me to verify any new cap before installation.

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 Post subject: Re: New capacitor values
PostPosted: Aug Wed 25, 2021 7:43 pm 
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fifties wrote:
I've had good luck with the caps I buy from Sal. I had one instance where a new yellow was bad, so that taught me to verify any new cap before installation.

Ditto for JustRadios........in fact, the ONLY bad cap in the last 10 years was a Nichicon from Mouser.. I have yet to see a Yellow film cap that was bad. Never seen the value off, but then I've never checked.......;)

I'm a "shotgunner", and---once the parts to be replaced are ID'ed, I slash and burn as quickly as possible. I go looking for bad parts only based on symptoms when the widget is running.---e.g the bad Nichicon, which pulled a key B+ line too low...... and I think generated some heat and smoke (or was it a noise?........;))

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"Voltage is fun to watch, but it's the CURRENT that does the work."


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