identifying all ceramic disc caps

[mikepukmel]

Thanks everyone for comments and info. I did try very hard to find some analysis on period ceramic disc capacitors like those used in 60's audio amps, but was not able. Someone must have cut a few apart, looked at materials, tested for e.g. temp stability etc.? Seems most ceramic disc capacitors listed on major components suppliers web sites are class 2 "general purpose". I wasn't able to find a sort key for 'class', which seems surprising to me, but then I don't have a lot of knowledge in this area. (working on that!). I guess, if you know what you're looking for, you know a particular manufacturer has a particular model capacitor that has the characteristics you want?

[Enzo]

I cannot say it too often, it is just a guitar amp. No special specs for caps or anything else. Fender used to use 20% tolerance resistors, tolerances on caps were all over the map, especially electrolytics. Honest to God, can caps typically had a tolerance of -20/+80%. Seriously.

Caps were a mature technology in the 1960s, and general purpose was just that - generic ccaps good for everyday use. They had special caps with known characteristics at voltage, and certainly temperature characteristics. And those matter in something like a UHF TV tuner, where a shift of a couple picofarads could mean a different channel. But in a guitar amp, none of that matters. Your typical treble cap in the tone stack was 250pf. If a 30 degree change on room temperature made it a 255pf cap, no one will notice.

Small ceramic caps like the 250pf are not very microphonic, but larger ones can be. SO I'd avoid ceramics like 0.1uf in the signal path for that reason. But in a circuit like the trem oscillator, they won't matter.

Characteristics I want? I want them to be real caps, not fakes. If it says 500v on the cap, I want it to be reliable at 500v. I want it to be in stock at my supplier. If the one I want is out of stock, by golly I'll order a different one with same ratings.

[vintagekiki]

https://www.anglia.com/literature/passiveBooks/CapacitorBookDownload.pdf

[mikepukmel]

https://www.anglia.com/literature/passiveBooks/CapacitorBookDownload.pdf

Thanks for the link!!

[mikepukmel]

I cannot say it too often, it is just a guitar amp. No special specs for caps or anything else. Fender used to use 20% tolerance resistors, tolerances on caps were all over the map, especially electrolytics. Honest to God, can caps typically had a tolerance of -20/+80%. Seriously.

Caps were a mature technology in the 1960s, and general purpose was just that - generic ccaps good for everyday use. They had special caps with known characteristics at voltage, and certainly temperature characteristics. And those matter in something like a UHF TV tuner, where a shift of a couple picofarads could mean a different channel. But in a guitar amp, none of that matters. Your typical treble cap in the tone stack was 250pf. If a 30 degree change on room temperature made it a 255pf cap, no one will notice.

Small ceramic caps like the 250pf are not very microphonic, but larger ones can be. SO I'd avoid ceramics like 0.1uf in the signal path for that reason. But in a circuit like the trem oscillator, they won't matter.

Characteristics I want? I want them to be real caps, not fakes. If it says 500v on the cap, I want it to be reliable at 500v. I want it to be in stock at my supplier. If the one I want is out of stock, by golly I'll order a different one with same ratings.

Awesome, thanks Enzo. So, if you were, say building an amp from parts, not a kit, and you had to chose, you mentioned small caps, not so microphonic (250pf, 47pf, 10pf) would you require class1 or is general purpose OK? The spec sheets some say class1 then mention a specific dielectric, I looked up the properties and it looks like mostly temperature stability? Okay but what else affects tone?

I got the idea from lots of discussions here, that for the most part mediocre components today are better than most components used in those old guitar amps.

[Enzo]

Life is too short, you can worry about parts when your life depends on it. Plain old vanilla parts will be perfect. What affects tone? Mostly the value.

Lots of people are very parochial about parts. Why they would never even THINK about using anything but "orange drops" in their amps. Foo, I prefer MAllory caps myself, not for any sonic reason, but I find them more convenient to install and arrange. Temperature stability? Oh come one. Your amp probably won't be used while the temperature is below say 60 degrees, and once you are playing for an hour, the innards will have come up to some temperature that will almost always be about the same inside.. SO temperature stability? It ain't like it sounds like a Fender when it is cool, but changes to a MArshall when it is hot.

I just looked up a CDE/Illinois 0.047uf film cap, temp coefficient was +/-100ppm/degree-C. That is 100 parts PER MILLION per degree. A fraction of a percent.

[vintagekiki]

https://industrial.panasonic.com/ww/products/capacitors/film-capacitors/film-cap-electroequip
Film Capacitors (Electronic Equipment Use)

http://www.humblehomemadehifi.com/Cap.html
Capacitor Test

https://sound-au.com/articles/capacitors.htm
Capacitor Characteristics

[mikepukmel]

THanks everyone!!

[mikepukmel]

Fender Capacitor Codes
CAP AE = Aluminum Electrolytic
CAP CA = Ceramic Axial
CAP CD = Ceramic Disk
CAP MPF = Metalized Polyester
CAP MY = Mylar
CAP PFF = Polyester Film/Foil

http://www.thevintagesound.com/ffg/deluxe_reverb_bf.html

https://images.reverb.com/image/upload/s--Ot5_DUXJ--/f_auto,t_supersize/v1598934362/efto7rcc2lbnq8xma58n.jpg

Thanks!!!

[mikepukmel]

Life is too short, you can worry about parts when your life depends on it. Plain old vanilla parts will be perfect. What affects tone? Mostly the value.

Lots of people are very parochial about parts. Why they would never even THINK about using anything but "orange drops" in their amps. Foo, I prefer MAllory caps myself, not for any sonic reason, but I find them more convenient to install and arrange. Temperature stability? Oh come one. Your amp probably won't be used while the temperature is below say 60 degrees, and once you are playing for an hour, the innards will have come up to some temperature that will almost always be about the same inside.. SO temperature stability? It ain't like it sounds like a Fender when it is cool, but changes to a MArshall when it is hot.

I just looked up a CDE/Illinois 0.047uf film cap, temp coefficient was +/-100ppm/degree-C. That is 100 parts PER MILLION per degree. A fraction of a percent.

Thanks Enzo! As mentioned, its more a 'for fun' thing for me. Curious what bits afffect the sound. So far, most of the fiddling Ive done hasn't positively affected the tone much.

[bsco]

And I say again, it is just a guitar amp, not precision lab gear. You might find film caps in one amp and ceramics in another in certain spots. The 63 in AB763 means 1963, if you amp is from 1970, chances are it is not identical. So don't assume there is some cosmic "correct" cap for each component. Old Fender amps were built with 20% tolerance resistors, and the tolerance on caps back in that era was all over the map. And pots? A 250k pot might measure at 400k. Ballpark is as close as it gets there.

I never knew that about date codes.....I take it then that will be the date code for the original design??

[mikepukmel]

If two ceramic disks have similar size and voltage rating, they are probably the same class. The better ceramics have lower dielectric constants and thus need to be bigger for same capacitance and voltage rating.
Measuring the capactive Q-factor with an LCR meter might give some info.

I also use the Q to tell between polyester/mylar, polypropylene and PIO caps.

Well, I got a few different ones from Mouser. Some, the data sheets say "Class 1 or class 2 or class 3 ... general purpose". And the others, say Class1, have better temp ratings, and are like 10x the cost. For me, couple of dollars more for a hobby. Would like to have a better way to measure caps, looking for a lcr meter. Are these ok to buy old used ones? I see cheaper ones in the 60 to 80 usd range. They seem to go all the way up many many multiples of the value of my car.

[Helmholtz]

Well, I got a few different ones from Mouser. Some, the data sheets say "Class 1 or class 2 or class 3 ... general purpose". And the others, say Class1, have better temp ratings, and are like 10x the cost. For me, couple of dollars more for a hobby. Would like to have a better way to measure caps, looking for a lcr meter. Are these ok to buy old used ones? I see cheaper ones in the 60 to 80 usd range. They seem to go all the way up many many multiples of the value of my car.

Each class comprises different ceramic materials. Class 2 ceramics may be microphonic. Better quality ceramics don't mean better sound. If there is an influence of caps on amp sound it's most probably the non-ideal properties.

Regarding LCR meters, many like the DE-5000 (https://www.amazon.com/Labs-DE-5000-.../dp/B005EMT8PC) .

[mikepukmel]

Thanks!