100K capacitor = 100pf?

[TallPaul]

I'm replacing ceramic disc caps in an 80's amplifier and I pulled 5 that had CGE 100K markings. They all measured 100pF. According to the Internet 100K is suppose to be 10pF. They are 10mm wide and thats kind of big for a 10pF. It only has to deal with 15v from the regulator. All the other ceramics of different values measured correctly according to the markings. Could these capacitors drifted that far in 30 years? The capacitors are CGE ceramic discs with epoxy coating.

 

[Harald Kapp]

According to the Internet 100K is suppose to be 10pF

Agreed.

Could these capacitors drifted that far in 30 years?

No way.

I'm replacing ceramic disc caps in an 80's amplifier

Shouldn't be necessary unless these are clearly defect.

 

[davenn]

According to the Internet 100K is suppose to be 10pF.

Agreed.

It's a trap that young players can fall into
it depends on if the 3 digit code is being used eg
100 = 10pF
101 = 100pF
102 = 1000pF etc

or if the cap is being marked in pF which is also very common, in which case 100 = 100pF

 

[Harald Kapp]

or if the cap is being marked in pF which is also very common, in which case 100 = 100pF

... which is the likely explanation here.

 

[kellys_eye]

I'd like to see a picture of the capacitors in question.

My own opinion is that they should be 0.1μF

It only has to deal with 15v from the regulator.

15V?? Regulator??? We're talking something like a pre-amp supply in a solid state circuit so 100pF?????????

Could be a problem with the way they're being measured????

 

[Audioguru]

100k picofarads is 0.1uF. The datasheet for a Texas Instruments uA7815 shows a 0.1uF capacitor at the output.
100pF will not work. 10pF is stray wiring capacitance.

 

[Harald Kapp]

100k

Assuming the measurement is correct, then the letter K is for +- 10 % tolerance.

 

[Robert_fay]

100k could be correct for 100pF. Some caps only change to the 3 digit when they go over the 100pF rating. So a 10pF would be marked as only 10 and the K would be tolerance 10%.

 

[kellys_eye]

....a 10mm wide capacitor on a 15V regulated supply line and 100pF??? Something is wrong with this... all the 100pF capacitors I have (rated at 50 to 100V) are 5mm in diameter and around 1mm thick.

 

[Robert_fay]

Any chance for a picture of the markings and cap. May clear up some options!

 

[Cannonball]

100k, the 100 is the value of the capacitor in pfs.

 

[BobK]

All my 10pF caps are marked 10 not 100. All under 100 are marked with pF in 2 digits. All my 100pF ones are marked 101. So 100 and 101 might very well both mean 100pF.

bob

 

[TallPaul]

And the winner is 100pF. I'm using a Fluke multimeter. They don't look like cheap junk ceramics. Back in the 80's this amp was $600. I had to replace the twin power caps and I don't do anything half a--. I replaced all the electrolytics with Nichicon Muse and all the ceramics with silver micas

 

[kellys_eye]

Which Fluke? Does it read accurately with other known-capacitances?

I'd like to see the schematic for the circuit in question to see how they can justify using 100pF on a 15V regulated line.....

 

[TallPaul]

Finally found the schematic and the Fluke was correct. 100K for CGE brand is 100p. I doubt if this cap company is in business anymore. Since it was early 80's it was pre-China junk era. More than likely they were made in the US

 

[kellys_eye]

It only has to deal with 15v from the regulator.

I call 'misdirection'...!!!

your schematic shows the capacitor to be RF suppression/decoupling across the inputs of the op-amp - perfectly suited to 100pF.

But, back to the original 'fault' - these capacitors rarely, if ever, go faulty. Even if they changed value by 500% it would likely make no appreciable difference to operation.