Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Dec Tue 07, 2021 7:05 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 9 posts ] 
Author Message
 Post subject: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Wed 25, 2021 5:21 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 4114
Location: Austin, Texas
I just removed one from the power supply of a Clarion and it is more than 12 times the volume of a modern cap.
Attachment:
1UF.JPG
1UF.JPG [ 721.71 KiB | Viewed 675 times ]

Jay


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Wed 25, 2021 6:53 am 
Member

Joined: Dec Sat 28, 2019 4:18 pm
Posts: 1124
Location: Corinth, TX
Are you comparing the size with a modern electrolytic or a modern film cap?

I just checked one of my 1 uf 1% standard film caps for my TO-5 and it is 1" long and a 1/2" in diameter. This looks like just a little more than half the volume.

John


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Wed 25, 2021 12:23 pm 
Member

Joined: Jun Fri 19, 2009 6:34 pm
Posts: 11171
Location: Long Island NY
And this is a good thing how?

Certainly if you are designing a new piece of equipment, the small sizes of modern film and ceramic caps are of great benefit. But there is a real downside for antique radio repair, and that is in AC current carrying capacity. In a radio power supply this would translate into ripple current.

Plastic film caps fall into two basic categories, AC caps and DC caps. AC caps are ones like motor run, EMI suppression and snubber, and power factor correction caps. They are designed to pass alternating current continuously and can deal with a certain amount of power. Their lead attachments and foils have low enough resistance, and they are physically big enough, that heating is not a problem. DC caps are used in electronic circuits where the voltages are predominantly DC with low voltage AC signals riding on it. It's not expected that there will be enough current passing through to affect a DC cap. AC rated caps are always bigger, heavier, and more expensive than DC ones. Needless to say, that old Clarion paper capacitor looks like it could have passed whole amperes of ripple current so it probably never broke a sweat when it was in operation.

ESR is another thing to consider. TRW-35 was a series of metalized polyester film capacitors. It's not possible to solder to metalized film so the lead end attachments are made with conductive glue. That glue has some inherent resistance so the ESR is higher than a crimped or soldered lead attachment. The metalized layer is also much thinner than a real aluminum foil plate, so its intrinsic resistance is much higher. The lead attachments and metalized layer are like putting resistors in series with your filter capacitors. They reduce the peak currents but that means higher ripple voltages and more residual hum. The capacitors will also get warmer as a result.

Clearly if you have to replace an original paper filter capacitor like the one in the Clarion, one should look for an AC type capacitor. AC motor run caps, ceiling fan caps, power factor caps, and EMI suppression and snubber caps are all available at bigger electronics distributors. You can find some on Amazon too. As for other kinds of caps, the spec sheets sometimes tell you up front if a capacitor is intended for AC or DC applications. Others do not specifically mention it. The way most designers look at it is this. If a capacitor is rated for AC service then it is a better grade, more expensive part. Manufacturers would want to brag about it by putting it on the spec sheet. If they don't say anything about AC operation or AC current ratings then it is safe to assume it's because they do not recommend the part for that kind of situation.

Note (added later). For the benefit of some who took me to task for ripple current ratings and ESR of film caps, be aware that these things are somewhat frequency dependent due to dielectric losses, skin effect, and inherent inductance. Therefore when spec'ing a cap for a conventional radio power supply you have to look at the frequency the cap will be working on (eg. 50/60 Hz, or 100/120 Hz). Ratings at 1 kHz or 100 kHz don't necessarily tell the whole story!

_________________
"Hell, there are no rules here--we're trying to accomplish something!"

Thomas A. Edison


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Wed 25, 2021 10:13 pm 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 22785
Location: Dayton Ohio
I've replaced many and have yet to have any problem replacing old wax paper caps with modern film caps of this size.

Has anyone else had issues with failures?

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Thu 26, 2021 12:19 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6675
Location: Montvale NJ, 07645
azenithnut wrote:
I've replaced many and have yet to have any problem replacing old wax paper caps with modern film caps of this size.

Has anyone else had issues with failures?

-Steve


Nope. The only failures I have seen are the ones laid out on paper- but I am not saying it won't/can't happen.
I have also used X2 AC rated film capacitors. They are available in some fairly large values.


Last edited by Scott on Aug Thu 26, 2021 12:25 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Thu 26, 2021 12:25 am 
Member

Joined: May Tue 30, 2006 4:46 pm
Posts: 11029
Location: Santa Rosa, CA
I strongly recommend FKP construction polypropylene caps. These contain a metal foil for high current capability; not just a vapor-deposited film on Mylar. Used these in my Induction Heater with great results.

https://www.wima.de/en/our-product-rang ... ors/fkp-1/

Not to be confused with MKP caps that are a "haze" of aluminum on a Mylar film.


Rich


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Thu 26, 2021 11:55 am 
Member
User avatar

Joined: Jan Mon 18, 2010 2:13 am
Posts: 22785
Location: Dayton Ohio
Hmm, there are a few WIMA MKP10 capacitors I installed as filter caps in one of my Spartons.
I'll run it more often to see how they hold up.

-Steve

_________________
Radio Interests
-Zenith
-Sparton
-Pre-War FM
Consoles and floor models, the bigger, the better!


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Thu 26, 2021 7:57 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4682
Location: Perrysburg, OH, 43551 U.S.A.
Rich, W3HWJ wrote:
I strongly recommend FKP construction polypropylene caps. These contain a metal foil for high current capability; not just a vapor-deposited film on Mylar. Used these in my Induction Heater with great results.

https://www.wima.de/en/our-product-rang ... ors/fkp-1/

Not to be confused with MKP caps that are a "haze" of aluminum on a Mylar film.


Rich

IMHO, the film/foil caps like the FKP would be my choice for replacing the paper caps in early radios' power supplies, but are overkill for typical coupling and bypass use. The metallize film types are fine in those locations.
John

_________________
“Never attribute to malice that which can be adequately explained by stupidity.”
― R. A. Heinlein


Top
 Profile  
 
 Post subject: Re: How big was a 1uF, 400VDC, paper cap in 1930?
PostPosted: Aug Thu 26, 2021 9:43 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 6675
Location: Montvale NJ, 07645
azenithnut wrote:
Hmm, there are a few WIMA MKP10 capacitors I installed as filter caps in one of my Spartons.
I'll run it more often to see how they hold up.

-Steve

It sounds like they would fail open, which would be the better option for failure. :wink:


Top
 Profile  
 
Post New Topic Post Reply  [ 9 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB