electrolytic capacitors

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electrolytic capacitors

Post by Guest on Mon Mar 10, 2014 8:21 pm

I'm working on a few GE 911D, 912D, 913D, 914D clock radios where one section of C1 is 75mfd @ 150WVDC. i did find some 200mfd @ 250WVDC. I was also thinking of using a 33mfd and 47mfd both @ 160WVDC in put them in parallel. Does anyone know of a good source, I have quite a few GE's

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Re: electrolytic capacitors

Post by Guest on Mon Mar 10, 2014 8:27 pm

This may be the answer, they have 100mfd @160WVDC

http://www.tuberadios.com/capacitors/

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Re: electrolytic capacitors

Post by Dr. Radio on Mon Mar 10, 2014 8:52 pm

I'm sure I'll get jumped all over for this, but when you increase the initial filter cap, you're putting more stress on the rectifier tube. I've never seen anything from the factory with anything higher then an 80 uF capacitor section that didn't use some sort of current limiting resistor after the rectifier and before the first electrolytic section. To me, 100 and more is too much without redesigning the circuitry.

I'd go 68 uF.

http://www.mouser.com/ProductDetail/Panasonic/EEU-EE2C680/?qs=sGAEpiMZZMtZ1n0r9vR22dN7zJS18SGVMfxUTZUK32s%3d
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Re: electrolytic capacitors

Post by Guest on Mon Mar 10, 2014 8:54 pm

That's just what I need! thanks Dr.  Very Happy 

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Re: electrolytic capacitors

Post by Wildcat445 on Tue Mar 11, 2014 2:08 am

I'm not familiar with those particular sets. Do they have PCB chassis?

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Re: electrolytic capacitors

Post by Guest on Tue Mar 11, 2014 8:05 am

Yes they do have PCB.

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Re: electrolytic capacitors

Post by Wildcat445 on Tue Mar 11, 2014 1:01 pm

In that case, you can remove the can caps and replace it with individual caps. Radial leads work well. You should be able to buy radial caps with 80mfd @ 160 volt ratings or even 250 if you prefer. You may not have room to parallel caps on that chassis.

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WC

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Re: electrolytic capacitors

Post by Guest on Tue Mar 11, 2014 1:06 pm

I was having trouble finding anything less than 100mfd with that working voltage but Doc gave me a link to one at mouser which is 68mfd @160 which will work fine.


Last edited by MEZLAW on Sat Mar 15, 2014 9:56 pm; edited 1 time in total (Reason for editing : change 86mfd to 68mfd)

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Re: electrolytic capacitors

Post by Wildcat445 on Tue Mar 11, 2014 1:09 pm

I have been buying caps from Mark Oppat. He gives good service and actually knows what a radio is. I like RadioDaze, but they have been moving, so I'm going to wait until they get settled.

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Re: electrolytic capacitors

Post by Guest on Tue Mar 11, 2014 1:12 pm

I've checked out Mark's website but haven't made any purchases yet.

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Re: electrolytic capacitors

Post by willy3486 on Tue Mar 11, 2014 1:13 pm

Last time I bought parts I got some from Allied electronics. So far I have been extremely happy with them. If you look for the inventory reduction prices or whatever they call it you can get great deals. I probably will start buying from them. Down side is if there is anything on backorder they won't ship until it is in or you pay a extra shipping charge. The up side is they have a large inventory and its also extremely easy to search for parts. Here is a quick search I did for caps.

http://www.alliedelec.com/passive-components/capacitors/?navigation=4294784051-4294793749-4294919623-4294920870-4294922159-4294937870-4294940248-4294943576-4294943579-4294943627-4294953243-4294959479-4294959632-4294959670

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Re: electrolytic capacitors

Post by Guest on Tue Mar 11, 2014 1:16 pm

Good link, thanks Willy.  Very Happy 

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Re: electrolytic capacitors

Post by Wildcat445 on Tue Mar 11, 2014 1:18 pm

I NEVER buy online. I want to speak in person with whomever is getting my hard-earned dough. That's why I like Mark, and RadioDaze and Gary at VM Enthusiasts. I can talk to a live body and, for me, that is worth a little extra money at times.

Regards

WC

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Re: electrolytic capacitors

Post by willy3486 on Tue Mar 11, 2014 1:39 pm

You can order from either the web page at Allied or call them up. I talked to my Represenitive and she sent me two large catalogs, one for home and one for work. Before that I ordered from Sal over at ARF. I got good ones from him as well.

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Re: electrolytic capacitors

Post by Ron Pond on Wed Mar 12, 2014 12:05 am

The maximum capacitor value for the the input side of the filter when using a 35W4 is 40uF.

The second filter capacitor's value is not as critical in that increasing its value will not load down the rectifier to the point of causing its failure, so use no more than 40uF at the filter input and anything up to say, 100uF to 150uF at the filter output.

Ron.
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Re: electrolytic capacitors

Post by Dr. Radio on Wed Mar 12, 2014 12:17 am

Ron Pond wrote:The maximum capacitor value for the the input side of the filter when using a 35W4 is 40uF.

The second filter capacitor's value is not as critical in that increasing its value will not load down the rectifier to the point of causing its failure, so use no more than 40uF at the filter input and anything up to say, 100uF to 150uF at the filter output.

Ron.


I'm sorry Ron, but I must disagree. I know you are referencing the tube manuals as I have seen that same statement as well, but its simply not the case in the real world.

Both GE and Zenith for example built millions of radios to the contrary.

Zenith was well known for their "80/40" caps--first section 80 uf.

GE used many 75 uf first section caps for their clock radios. These were done with no current limiting resistor directly off the 35W4 cathode.

That's why I suggested the 68 uF caps to MEZ.

Also, nothing wrong with Allied, but don't they have a minimum order requirement?
Mouser has no minimum order, and yes, you can even call a real person to place an order.

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Re: electrolytic capacitors

Post by Ron Pond on Wed Mar 12, 2014 6:59 am

Point well taken.....I don't see too many American GE or Zenith radios around here although my point about increasing the second filter capacitors value is a valid one.

Having said that I have never seen any tube radio here that uses a higher first filter cap value than that of the second filter cap. It seems electronically counter intuitive to do so in my opinion.

Yes, I used my specs books to find the 35W4 input filter capacitor value but sometimes radio manufacturers get it wrong also.

Well known are some of the older Zeniths with power transformers that were marginal in their current delivery capacity in conjunction with early 6X5 rectifiers that could not possibly handle the B+ current required by multi-tube consoles.

Would the radios you refer to that use 80/40 caps the way you described hum excessively if you used the same capacitor with the 40uF as first filter and the 80uF as second filter? May be worth trying.

Best regards,
Ron.
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Re: electrolytic capacitors

Post by 35Z5 on Thu Mar 13, 2014 3:23 am

Well just because overrating recommended cap value was done doesn't mean it's actually good for the rectifier tube... And while it may apparently work just fine, can you say for sure tube life isn't shortened??? Of course now days when such radios are turned on maybe once a month, probably take 25 years to develop problems...

Regardless of what the factory did, I'll add a 33 ohm current limiting resistor between cathode and first filter cap section, especially if it's over 50mfd...
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Re: electrolytic capacitors

Post by Dr. Radio on Thu Mar 13, 2014 7:04 pm

Tom,

I can't say for sure the methodologies behind the designs, but although the name of the game is "cost-effectiveness", I seriously doubt the engineers would knowingly put excessive stress on some designs and "hope for the best", even with the over-shadowing of the bean counters. I could see GE not caring as there base consumer product line was marketed to those who didn't want to spend much, however Zenith built there reputation superior reliability so I seriously doubt the mentality of "who cares if the radio goes thru rectifier tubes like no tomorrow" came into play.

It's interesting to note that late 1940s and very early 1950s designs of Zeniths used a 22 ohm @ 1 Watt surge resistor with there first section 80 uF cap. Not long after, this mysteriously disappeared.

The one thing that can be argued though, is there are millions (billions?) of radios that were built by many many manufacturers with larger then 40 uF input caps and no surge resistor. I wouldn't be concerned about modifying the circuitry. You can if you want, just my 2 cents.
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Re: electrolytic capacitors

Post by 35Z5 on Thu Mar 13, 2014 11:20 pm

Well the tube manual specs never changed, thus I suspect the bean counters won in the early '50s when competition stiffened due to the market being saturated after WWII...

So rectifier life was shortened from five to say four years on average, who cares??? The retail price on 35Z5 & 35W4 were less than $1.50 through the 50s and 35W4 was as cheap as $1.05 in the mid 60s(wholesale as cheap as $.50)... Almost no one was going to complain about a total bill of $3.50 or $4.00 to the local shop to have their $20-$30 radio repaired...  


BTW
I have seen over capped rectifiers arc if power was cut and reapplied while tube was still hot(not much I haven't tried over the years), if nothing else the surge resistor will limit damage in this condition...
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Re: electrolytic capacitors

Post by Guest on Sat Mar 15, 2014 9:58 pm

Here's one of those very radios on Ebay where the seller claims to have replaced both sections with 100mfd @160WVDC for both sections!  Shocked 

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electrolytic capacitors

Post by Ed in W. PA on Wed Mar 19, 2014 11:48 pm

This question is in reference to what Dr. Radio touched on regarding causing additional stress on the rectifier tube by increacing the capacity of the initial filter cap. What if one were replaceing a selenium rectifier with a modern diode and increaced the capacity of the filter cap? The project on my bench right now is a Zenith Am-Fm receiver model M-723 ( approx 1965 ) and the filter cap is 80-60-40 @ 160 . Do you think that the values are as critical in this case as in a set with a rectifier tube?
Thanks, Ed

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Re: electrolytic capacitors

Post by 35Z5 on Thu Mar 20, 2014 12:19 am

A 1N4007 is rated at 1A continuous, that's 10x of a 35W4 ratings and can stand a 30A surge which is 50x a 35W4 ratings... Discharged a cap has a very low ESR, so can load a tube well beyond it's ratings without a current limiting resistor...

While it's probably unnecessary to add capacitance the 1N4007 isn't going to care, but you will need to add resistance between the rectifier and first filter cap as you B+ will probably be in the range of 25-40v too high...
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