Replacing a cap with higher voltage, same capacitance.

[circuitmonkey]

I am working on a slew of Seeburg Juke box boards, and while trying to procure the caps.... lets just say I ran into a few snags. These were built in the early 70's and some of the caps on the driver and amp boards have some small uF values. One in particular is a 75v 20uF axial Lytic(that is what is listed in the schematic). I can't find a new replacement(in regards to voltage). My understanding is(keep in mind, I am not real bright) as long as the capacitance is the same, a higher voltage can be used. I can find 100V 20uF axials(pricey), but I also see them rated to 450v(strangely not as pricey). Can someone with some experience in this give me a clue? Maybe in crayon? Thx.

[redwire]

Re: Replacing a cap with higher voltage, same capacitance.

Looking for exact old capacitor values does not always go well.

In the old days you could buy 5uF or 20uF or 50uF, but that became globally standardized to 4.7uF, 22uF, 47uF etc.

It's best to use the EIA E-12 values for parts. They are in decades, so "220" means preferred values are 0.22 or 2.2 or 22 or 220 or 2,200 etc.

I would use a 22uF part. Tolerance on electrolytic capacitors is ±20% so a bit bigger value is fine.
The 75V rating is also a bit odd, it became 63V, 80V, 100V as popular offerings from companies.

Radial is lowest cost but you'd have to add a flying wire, spaghetti tubing and a dab of silicone glue, to replace an axial part.

Some axials by Illinois Capacitor, Nichicon at Digikey like 1572-1095-ND but a vanilla part 2,000hr life 85°C, not long life or high temperature -those parts last longer.

Such as United Chemi-Con KYB 22uF 80V $0.50 and 7,000hrs 105°C. Small compared to the older parts, so easy to put in there.

Just Radios sells axial electrolytics and oddball (new) parts for antique radio restorations.

[circuitmonkey]

Re: Replacing a cap with higher voltage, same capacitance.

Thank you! I put in my order and will update when everything is installed.

[Santa Claus]

Re: Replacing a cap with higher voltage, same capacitance.

As redwire wrote, the tolerance are quite high so don't be to worried about the capacitance value. To use one with 10 or 20% higher value is normally OK. Since electrolytic capacitor quite often are used as decoupling at supply voltage it is better to go up than down in value.

Regarding the voltage this is the maximum voltage the capacitor is designed for. Replacing with a higher voltage is no problem. Based on life time (MTBF) it is an advantage to not use capacitors close to there maximum voltage.

[circuitmonkey]

Re: Replacing a cap with higher voltage, same capacitance.

Looking over my notes, and I could verify by checking my order, I substituted 12V 50uF caps with 16V 47uF caps, and 6V 50uF caps with 10V 47uF caps. These were the only two instances where I used a lower capacitance rating as I would assume since capacitance goes down over time (generally tossing anything with 10% or greater loss) that as long as the caps are good, 47uF should be enough. Everything else I was able to keep close at slightly above. Should I order some bigger caps or do you think these will suffice? I should state, after I restore function to the amp and give it a thorough inspection with slow run up on the Variac, I plan to put a signal through it and check for distortion on the O-scope. Some of these caps may be replaced again with something better. I found it hard to spend a lot not knowing the variables. Still have plenty of issues not related to the caps such as resistors on the driver board that should have a value of 100 Ohms measuring 180 Ohms out of circuit and over 200 in circuit. Little things like that. So far, no dead shorts. But if I do come across some of the transistors being fried in these, I have a feeling it is going to be a real headache trying to find equivalents. Feel free to chime back and thanks again for your help.

[circuitmonkey]

Re: Replacing a cap with higher voltage, same capacitance.

Some pics of the disaster occupying my bench.

[budm]

Re: Replacing a cap with higher voltage, same capacitance.

If I were you I would replace those carbon composite resistors with carbon film type at least.
BTW, you can also use 56uF cap in place of 50uf.
I.E. https://www.digikey.com/products/en/...tors/58?k=56UF

[circuitmonkey]

Re: Replacing a cap with higher voltage, same capacitance.

I looked into your resistor comment and you are right. It seems that metal film might be the best composition for audio resistors. Any reason I might not want to use those? I had already purchased Nichicon caps, so I'll check the signals once I restore function before I grab something a little longer lasting. I'm making some cheat sheets for quick reference as I have at least 10 of each board. It is going slow, but I took this job to learn and that I am. I appreciate all the input. Here's some more pics. Burnt/blown traces, components, bad.... everything. You know, dirty circuit porn. Enjoy!

[budm]

Re: Replacing a cap with higher voltage, same capacitance.

When those composite resistors start drifting in value, they can affect the biasing of the semiconductors which will cause problem.

[circuitmonkey]

Re: Replacing a cap with higher voltage, same capacitance.

Just an update: I haven't fallen off the planet. I have been building a capacitor leakage tester designed by Paul Carlson. I have a lot of caps to test on these boards and it seems to me having a good way to test for DC current leakage would be prudent. This required etching a PCB and populating. We are now at the testing and debugging stage, so I hope to have it running on the bench soon. I'll include some pics and tests when I get back to these amp boards. Thx again for all your input.