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 Post subject: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 12:30 am 
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Location: central wisconsin, 54449
Hi to everyone. I am about to order some electrolytics for a power supply, 1940's radio
I know enough to get 105 degrees if possible.
I would like some information on 2 variables

do I want high ripple or low ripple?
do I want high esr or low esr?
my thanks in advance


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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 12:45 am 
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Location: Rochester NY USA
Any modern caps in these values will have adequate ratings for ESR and ripple current. Ripple current requirement for FIRST cap after rectifer is similar to DC current drawn - so perhaps 80 mA? (Current is negligible in other caps). Of the few axial 22 uF ones available at DigiKey, ratings were 130 mA and up.

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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 2:20 am 
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what is the rectifier ?

I absolutely recommend using 500 volt electrolytics (Illinois caps from AES) for the filters and 630 volt yellow capacitors for the small values.

the current inrush on the filters from a directly heated cathode rectifier will cause these capacitors to easily see voltage near or above 450v for a few seconds before it settles down.

i exclusively use Illinois 500 volt electrolytics in any radio or amplifier that uses a directly heated cathode rectifier. i never want any new capacitor to see anything close to its rated voltage, even for a few seconds.

opinions will differ, but i will stick to mine.

steve

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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 2:42 am 
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Location: 253 Blanche St. Plymouth, MI USA
I recommend using 450v rated electrolytics for most AC power radios main filter caps. I have used and sold them for over 30 years, probably sold over 50,000 filter caps alone (plus maybe 250,000 mylar caps) and have never once had a failure, other than the rare case where a customer installs an electrolytic backwards. You will pay dearly for the extra 50v of rating to get 500v, the numbers I quoted above do not lie, the 450v rated ones are extremely reliable.
Only case you will need higher than 450v is for a few radios made before 1933 that ran type 10 or type 50 output tubes. Those will need 600v rated filter caps as they ran higher B+ for those early triode tubes.

I sell filter caps in 4-5 values in each of the following voltage ratings : 50v, 160v, 250v and 450v . This covers 98% of all needs. Remember the values can be fudged a lot on MFD., so a 12mfd can be replaced by a 10 or 22mfd cap. Only the first filter cap that is tied directly to the rectifier tube need be kept within -20%/ +50% of original value, the others can be doubled if you like, for better hum reduction. The reason the to keep tighter on the first filter cap is it will raise the B+ voltage and put greater stress on the rectifier tube during turn-on surge.

ESR rating basically calls out the condition of the capacitor, LOW ESR means its in good condition.

Stay far away from "audiophile" type websites that are designed to put their bull***t into airy fairy terms that lure you into buying extremely overpriced "solutions" to your simple needs. Read here on the ARF for the real "down to earth" facts, usually. there are some good servicing videos on Youtube too. Also, I am one of the presenters at the big Vintage Electronics Expo in Kalamazoo, MI July 19-20 (I am slotted for 9:30am-11am on Saturday) talking about "Repair Tricks and Tips" as I have done for many years... please come to this event if you can.
Mark Oppat
Antique Audio


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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 3:34 am 
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Location: Long Island
It’s absolutely not true that any capacitor within those values will have adequate ripple current or ESR ratings. Some modern 105-degree C and ultra small types are rated for 25 mA or less ripple current. They won’t last long in a five or six tube radio where average load current is 50 mA to 60 mA. As a rule of thumb, circuit designers use capacitors that have a maximum ripple current rating three times the DC load current. This is to prevent the temperature rise of the capacitor from inadvertently running away (temperature rise increases resistance which further increases temperature, until the capacitor roasts itself).

If you are having trouble finding 105 degree caps, consider going back to 85 degree ones. In many cases they’re one and the same, only the 105 degree caps are rated for less ripple current and/or less hours of operating life! In any event, a 105 degree cap buys you very little unless you really intend to run it that hot. Unless there’s a circuit fault or a defect, most electrolytics eventually die by drying out, and that will happen regardless of the temperature rating.

ESR is of little consequence in tube radio circuits. Generally speaking, modern electrolytic capacitors have higher ESRs than ones made 20 to 70 years ago, but they’re also “tweaked” for higher frequencies which tends to compensate. But keep in mind that both ripple current and ESR are determined in part by frequency. Having great specs at 100-kHz does you no good in a linear power supply where the ripple current is at 60-Hz or 120-Hz.

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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 5:36 am 
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Location: central wisconsin, 54449
the radio here is the Stromberg carlson 535m, and the schematic indicates a 5u4g for the rectifier tube


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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 1:32 pm 
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I'd go 40uf 500v, 30uf 450v, 15uf 350v, and 15uf 350v.

https://www.studioelectronics.biz/sunsh ... ail&p=1584

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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 2:38 pm 
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For the 5U4, the data sheet suggests a maximum of 40uF for the first filter. That's what the Rider's shows for a 5Y3---where do we see a schematic for 535M?

Practical observation:
Many of us routinely install caps from Sal or JustRadios where we have no specs except rated voltage.

Random comments:
--no need for anything better than 85C. If you want to upgrade, i'd recommend looking at the lifetime specs.

--ESR is a real spec, not just an indication of condition. ESR is related to the ripple current rating, and the issue is simply heating, which will in turn affect lifetime

--A good rule for voltage rating is 1.5X the steady-state working voltage

--You can reduce ripple current and make life easier for the rectifier by reducing the size of the first filter--increasing the others as needed.

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"Measure voltage, but THINK current." --anon.


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 Post subject: Re: ordering capacitors for power supply what specs?
PostPosted: Jun Mon 03, 2019 8:54 pm 
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Location: Central PA 16801
pixellany wrote:
--You can reduce ripple current and make life easier for the rectifier by reducing the size of the first filter--increasing the others as needed.


just like delco did NOT do here.

https://antiqueradios.com/forums/viewto ... 6&t=359883

i never saw a 60 uF on a 5Y3, but i completely understand what lorenz is saying.

when i installed the 500 volt electrolytics, i got away with a 47 for the first filter and adding another 10 to it did nothing.

anyone can do whatever they want, but i *highly* recommend using 500 volt capacitors for the electrolytics. it is common for them to see 495 to 510 volts at startup in many transformered radios and amplifiers that run a steady B+ of 325 to 375 volts on the cathode of the rectifier.

i don't think these new capacitors, even the good nichicons and panasonics, want to see their working voltage exceeded, even for seconds. they don't make them anymore like the Sprague TVL Twist-Lock Lytics of days gone by which actually listed a working and surge voltage.

in a transformered set with steady B+ above 250 volts, for the extra 50 cents to a buck twenty-five, why *not* use 500 volt lytics in situations like this ?

(rhetorical question, no answer needed)

steve

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