Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently May Wed 23, 2018 2:09 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 17 posts ] 
Author Message
 Post subject: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 12:56 am 
Member
User avatar

Joined: Jul Sun 23, 2017 4:01 pm
Posts: 47
Location: Mint Hill, NC
Easy question for you guys....
I'm restoring a Philco 46-250 that has 3 electrolytics: 30mf, 25mf & 20mf all 150 volts . Can I replace them with 33mf, 22mf & 22mf all 160 volts?
I'm thinking yes, but wanted your opinions.

Thanks,
Philco47


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 1:18 am 
Member
User avatar

Joined: Jan Mon 05, 2009 4:09 am
Posts: 1221
Location: Hudson, MA
Yes, but if you don't have the caps yet I would go for a 27uF to replace the 25uF

_________________
Eddy


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 1:26 am 
Member
User avatar

Joined: Jul Sun 23, 2017 4:01 pm
Posts: 47
Location: Mint Hill, NC
I already have 22's and 33's. I checked Radio Daze, they don't have 25's or 27's.


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 2:48 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 32464
Location: Maryland 20709, USA
Philco47 wrote:
Can I replace them with 33mf, 22mf & 22mf all 160 volts?
Addressing only the voltage rating...

I always recommend using caps rated at least 200 volts, preferably 250 volts.

The 150v caps were under-rated even for the lower AC line voltage at the time.

They (and 160v caps) are certainly under-rated for today's higher line voltages.

And even if you could squeak by under the normal line max, 160v caps provide no safety margin in the event of line transients or noise pulses.

The added safety of 200v parts is really cheap.

- Leigh

NB: The peak voltage of a 117v line is 165 volts; of a 125v line... 177 volts.
And those have NO margin for transients or noise.

_________________
73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 5:52 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27260
Location: SoCal, 91387
Leigh wrote:

NB: The peak voltage of a 117v line is 165 volts; of a 125v line... 177 volts.
And those have NO margin for transients or noise.

So out of curiosity, about how much voltage over 160 could caps rated at that value tolerate before exploding, on the average?

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 6:50 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 3992
Location: Sunnyvale CA
Philco47 wrote:
Easy question for you guys....
I'm restoring a Philco 46-250 that has 3 electrolytics: 30mf, 25mf & 20mf all 150 volts . Can I replace them with 33mf, 22mf & 22mf all 160 volts?
I'm thinking yes, but wanted your opinions.


You would *probably* be OK with 160V, since you have a tube rectifier that doesn't have much overshoot at startup. After startup, in steady-state operation, they will be seeing something like 125V. However, if you are going to have to buy them new anyway, Leigh is right, you would be better off with 200 or 250V ratings. It will give you much more margin at startup for negligible extra cost.

Brett


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 6:55 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 3992
Location: Sunnyvale CA
fifties wrote:
Leigh wrote:

NB: The peak voltage of a 117v line is 165 volts; of a 125v line... 177 volts.
And those have NO margin for transients or noise.

So out of curiosity, about how much voltage over 160 could caps rated at that value tolerate before exploding, on the average?


Impossible to say. When you have a selenium or diode for rectification, they will routinely see 170-175 volts for a fair bit of time at startup, maybe 10-15 seconds in some cases. I have never seen one blow or short in those conditions - but it's not recommended or a good idea. That's for aluminum electrolytic caps of modern manufacture.

Brett


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 10:08 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2746
Location: Nr London, England, SS1 3PT
Those 160V ones could be small and have low ripple current ratings which might not suit the first 20mF. I always fit bigger, higher voltage ones, check the ripple rating and use a good makes like Panasonic or Nichicon.

Gary


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sat 13, 2018 5:05 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 4167
Location: Charleston, W.Va.
Philco47 wrote:
Easy question for you guys....
I'm restoring a Philco 46-250 that has 3 electrolytics: 30mf, 25mf & 20mf all 150 volts . Can I replace them with 33mf, 22mf & 22mf all 160 volts?
I'm thinking yes, but wanted your opinions.

Thanks,
Philco47

Hi Philco 47,
Good practice with tube rectification is to keep the input filter cap at or near its original value; output filter cap(s) can safely be increased in value. In fact this often gives improvement in hum reduction. In your Philco 46-250, the input filter cap is the 30mfd; 25mfd and 20mfd are the first and second output filter caps, respectively. So using the new caps you already have on hand, my choice to replace 30mfd/25mfd/20mfd would be 33mfd/33mfd/22mfd.

Regarding voltage ratings for AC/DC radio electrolytic caps, we have had much discussion (and some disagreements) on this in the past and I am not going to renew it now. All I will say is that on a radio like this 46-250 I would personally use 160v caps. Although certainly nothing wrong with using ones of higher voltage rating if you happen to have them.

_________________
Poston


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 1:22 am 
Member
User avatar

Joined: Jul Sun 23, 2017 4:01 pm
Posts: 47
Location: Mint Hill, NC
Thanks for all the replies. I'll use the 33mf, 33mf, 22mf combination that Poston suggested. But may order more and up the voltage. Thanks for the schooling.


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 1:33 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12381
Location: San Jose, CA USA
Since this is a regular All American Five, use of 160 V filter caps is a good choice. The voltage across the caps in an AA5 never exceeds 140 V even during warm up. The original caps rated at 150 V were not underrated in any way, and using 160 V caps today (the standard voltage available in that range) gives even a little better margin than the originals had. Nominal line voltage has increased by 3 volts (from 117 VAC to 120 VAC) in the intervening years, so adding 10 V to the filter rating gives some extra margin.

Note that the AA5 circuit is fairly unique in this regard. Its rectifier tube warms up last for several reasons, and therefore there is no turn-on voltage rise as is seen in lots of other radio circuits. What you'll see if you measure the voltage across the filter caps in an AA5 is a slow rise from zero volts up to around 120-130 V after full warm up and the radio is playing. It never comes close to the theoretical peak voltage of 167 V.

Even if the radio has some type of circuitry failure, such as an open cathode resistor on the output tube, or an open output transformer -- both of which drastically cut the current being drawn from the power supply, the voltage on the filter caps still doesn't exceed 160 V, since there is enough remaining load in the rest of the radio to keep the voltage down.

So although there is no harm in using a cap rated at higher than 160 V, the is also positively no benefit in doing so.

In other types of radios, such as those using a selenium rectifier, or transformer powered radios with rectifiers with filament cathodes (like 80 or 5Y3), there can be a significant warm-up voltage surge. So in most radios other than AA5s (or the very similar 6-tube circuits), you'll want to provide some extra voltage margin to accommodate the warm-up surge and various failure modes that could place a high voltage on the caps, leading to subsequent damage if they fail by shorting.

_________________
Tom K6VL


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 2:04 am 
Member
User avatar

Joined: Mar Sun 11, 2007 6:55 am
Posts: 9703
Location: Mission Viejo, southern California
Tom Albrecht wrote:
What you'll see if you measure the voltage across the filter caps in an AA5 is a slow rise from zero volts up to around 120-130 V after full warm up and the radio is playing. It never comes close to the theoretical peak voltage of 167 V..
Thanks, that is useful information. I'd never before bothered to measure it, but now it will be fun to put a meter on the next AA% I restore and watch it.

_________________
many of my radios http://s269.photobucket.com/user/FSteph ... t=3&page=1


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 6:12 am 
Member

Joined: Aug Wed 24, 2011 4:35 am
Posts: 3992
Location: Sunnyvale CA
Tom Albrecht wrote:
Since this is a regular All American Five, use of 160 V filter caps is a good choice. The voltage across the caps in an AA5 never exceeds 140 V even during warm up. The original caps rated at 150 V were not underrated in any way, and using 160 V caps today (the standard voltage available in that range) gives even a little better margin than the originals had. Nominal line voltage has increased by 3 volts (from 117 VAC to 120 VAC) in the intervening years, so adding 10 V to the filter rating gives some extra margin.

Note that the AA5 circuit is fairly unique in this regard. Its rectifier tube warms up last for several reasons, and therefore there is no turn-on voltage rise as is seen in lots of other radio circuits. What you'll see if you measure the voltage across the filter caps in an AA5 is a slow rise from zero volts up to around 120-130 V after full warm up and the radio is playing. It never comes close to the theoretical peak voltage of 167 V.


In fact, I tested it today on a Philco 48-250 (which is the same radio with a few tubes changed) and of course, it does exactly what you think it does. I would still rather use 250V caps for margin, but in fact, mine has 160V caps because that's what I had and my need for reliability on a radio that might someday be used for up to 3 hours to listen to a Giants game, it's reliable enough.

Brett


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 9:24 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27260
Location: SoCal, 91387
Brett_Buck wrote:
Tom Albrecht wrote:
Since this is a regular All American Five, use of 160 V filter caps is a good choice. The voltage across the caps in an AA5 never exceeds 140 V even during warm up. The original caps rated at 150 V were not underrated in any way, and using 160 V caps today (the standard voltage available in that range) gives even a little better margin than the originals had. Nominal line voltage has increased by 3 volts (from 117 VAC to 120 VAC) in the intervening years, so adding 10 V to the filter rating gives some extra margin.

Note that the AA5 circuit is fairly unique in this regard. Its rectifier tube warms up last for several reasons, and therefore there is no turn-on voltage rise as is seen in lots of other radio circuits. What you'll see if you measure the voltage across the filter caps in an AA5 is a slow rise from zero volts up to around 120-130 V after full warm up and the radio is playing. It never comes close to the theoretical peak voltage of 167 V.


In fact, I tested it today on a Philco 48-250 (which is the same radio with a few tubes changed) and of course, it does exactly what you think it does. I would still rather use 250V caps for margin, but in fact, mine has 160V caps because that's what I had and my need for reliability on a radio that might someday be used for up to 3 hours to listen to a Giants game, it's reliable enough.

Brett

That's a good point. Let's face it, most of these AM only sets don't really get used all that much, so 160 volt caps in this case should be sufficient. Now if you're restoring a set that will be a daily driver, then the 250 volt overkill rating might be indicated (IMO more for peace of mind than as an actual safety feature).

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 10:14 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 2746
Location: Nr London, England, SS1 3PT
But if you don't use them much, like after being left for a few years, do they go bang when you switch them on with the 160V caps? Not going to have to lose much dielectric for that to happen. If you have them then chance it but if buying always add on 50% for margin and the ripple current rating will be higher too. Costs only cents more.

Gary


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 10:27 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 27260
Location: SoCal, 91387
Lol, we could debate this ad nauseam, and actually have in the past. Best answer, it seems, is to simply use what you're comfortable with. In my case, replacing 150 volt caps with 160's, and considering that the line voltage hasn't increased by that much, seems to make sense (although I confess to not being the brightest bulb on the tree... :wink: ).

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


Top
 Profile  
 
 Post subject: Re: Electrolytic Replacements?
PostPosted: Jan Sun 14, 2018 8:32 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12381
Location: San Jose, CA USA
Adding extra voltage margin may not help very much with long term reliability. The technical literature for one of the current major manufacturers of electrolytic caps indicates the following:

1. Long term operating voltage should not exceed the rated working voltage.
2. If the capacitor is consistently operated near its maximum temperature rating, then providing some margin below the rated working voltage can extend life.
3. For isolated periods up to 1 minute, an electrolytic capacitor can withstand a surge in voltage up to 10% over the rated voltage.

So unless your cap is in a location that is really quite hot (resulting in the cap being at a temperature near 80 C for caps rated at 80 C or near 105 C for caps rated at 105 C), it's fine to operate them all the way up to their rated working voltage.

Brief isolated surges in voltage up to 10% over the rated voltage are OK.

In an AA5, with the voltage basically never going over 130 V (and maybe 140 V with a weak output tube), there is plenty of voltage margin using a 160 V cap, even if the capacitor is in a hot location. And there is no warm-up surge in an AA5.

And in most AA5s, the cap will never be anywhere near 80C or 105 C. You may think it can get warm, but try actually putting a temp probe firmly attached to the aluminum jacket of an electrolytic (not just measuring the air temperature near the cap), and you'll see that getting the cap over 60C is rare indeed (even for an FP cap standing right next to a 50L6). Most don't even make it to 40 C.

So your 160 V cap has plenty of margin in an AA5.

_________________
Tom K6VL


Top
 Profile  
 
Post New Topic Post Reply  [ 17 posts ]  Moderators: Marcc, Norm Leal

All times are UTC [ DST ]


Who is online

Users browsing this forum: Google Adsense [Bot] and 15 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB