Electrolytic question

[radio nut]

My electro's in my muntz set are 450 volt. The diagram calls for 500 volt. Even new stock electro's formed before installation run a little warm, but the b plus line is higher than the 70-75%percent of the voltage of the caps them selves. I have read here that the cap voltage rating is a max . I can get 500's from just radios......but would 600 volt caps last longer than 500 since they would not be getting pushed too hard?

[bob91343]

Electrolytic capacitors are a strange breed. They work best when operated near their voltage rating but have short lives at higher levels. Today's higher line voltages imply a need for the higher ratings.

Measure the voltage you have and add about 10% and you will probably be good to go.

I don't think using 600 V units will give you any real benefit unless you find the voltage to be dangerously close to 500 V.

[earlyfilm]

If your Muntz has a solid state rectifier, especially if it has been upgraded from selenium, then the capacitors may temporarily exceed their voltage ratings during tube warm up. This will shorten their life.

Tube rectifiers like the 5U4 & 5Y3 intentionally have a controlled filament warm up to prevent this from happening.

[radio nut]

B plus voltage should be about 370...but is closer to a little over 400 due to outlet voltage of 125 as opposed to 117 on the diagram for voltage checks. .
I thought that electro's should be room temp and not warm. Also that they should be run at about 70- 75 % of rated voltage.
My electro's run warm but not hot. Also this set uses a 5u4 as rectifier

[radio nut]

Originally Posted by bob91343

Electrolytic capacitors are a strange breed. They work best when operated near their voltage rating but have short lives at higher levels. Today's higher line voltages imply a need for the higher ratings.

Measure the voltage you have and add about 10% and you will probably be good to go.

I don't think using 600 V units will give you any real benefit unless you find the voltage to be dangerously close to 500 V.

Going off of memory my b plus line is running 413. so 10% higher is almost 450.....so I need 500's then, right?

[Kevin Kuehn]

I don't know how electrolytic caps could stay at room temperature under load. Technically that's impossible if they're filtering AC. If they are used in a voltage doubler they're working even harder. Slightly warm shouldn't be a problem. Just watch the peak voltage across them at turn on.

[Tom Albrecht]

The 10% guideline is a good one. Derating to operating at just 75% of rated voltage is much more conservative than what the original designers did.

I find many sets exceed the voltage ratings of the capacitors during warm up, and they seem to survive just fine. Usually electrolytic caps have a surge rating which is higher than the working voltage. Although it is stated above that a 5U4 or a 5Y3 has a controlled warm up speed, I find they still warm up and produce voltage 2 or 3 times faster than the rest of the tubes (with indirectly heated cathodes) warm up, so even sets with tube rectifiers have a big voltage surge during warm up.

Although electrolytics warm up very slightly when in normal use, I would say most people almost wouldn't notice it. If it feels obviously warm within 10 minutes or so, something isn't right. However, make sure it isn't simply being heated up by nearby tubes. I agree with the statement above that electrolytics used in voltage doublers have much higher peak currents and will warm up a little more.

If yours are getting quite warm, I'd look for something other than just a surge voltage that merely approaches the working voltage temporarily during warm up.

[Username1]

When talking about capacitors its millions of joules of electrons moving across the plates opposing a change in voltage from one plate to another..... Capacitors are constant voltage items, and inductors are constant current items, they resist a current change in the line with their stored electromagnetic field. Both of these items work in a power supply to try and maintain a nice ripple free DC source. Working voltage, peak voltage, average voltage, Which was actually posted on the side of an electrolytic....? Unless you made it, you don't know... So when replacing go 10-20% above the highest V. you see in the working set..... Another reason it's good to fix the set before ordering new caps.... Is B+ above design specs...? Below...? Which is normal....? Was the set made with parts from the lowest bidder....? Does the cap even come close to the ratings posted on the side....? I usually buy electrolytics rated 50V above what I'm taking out, 75 to 100 if I can't get the 50. Last choice is to put back exactly what came out, never go under the rated voltage.

[old_coot88]

Originally Posted by earlyfilm

If your Muntz has a solid state rectifier, especially if it has been upgraded from selenium, then the capacitors may temporarily exceed their voltage ratings during tube warm up. This will shorten their life.

Tube rectifiers like the 5U4 & 5Y3 intentionally have a controlled filament warm up to prevent this from happening.

Um.. not to be picayunish but 5U4 and 5Y3 are direct-filament types that warm up quickly and put full B+ onto the filters before the rest of the tubes begin conducting and pull the B+ down.
There are other 5V rectifier types that have indirectly heated cathodes and give controlled warmup. 5V4, 5CG4 etc. come to mind.

[radio nut]

ok, cool. all input is being read and reread. My electro's only get warm. Mine are mounted under the chassis and not stuffed into the original cans.
Seems to me the lectro's in my radios were always cold. BUT, I have been in this muntz tv and had to replace more parts than I care to think about. So maybe I noticed them due to all the time "under the hood"!