Dissipation spec in capacitors

[pjd3]

Hello,
So as I bring in old and new caps into my work from home to check them on our expensive LCR bridge, there is a spec it reads called "D" which I take as the dissipation factor.

A new Mallory 150 will typically show a value of around .0003 or so, but, one of my old unused NOS film caps (I believe) will be more towards .002 or so. Its greater than the new Mallory's by a decade and I suppose something like that shouldn't come as a surprise, and I'm not suspecting that this would have any notable effect on the performance of the amp I'm about to build.

However, I'd be interested should anyone be familiar with the limits and implications of this aspect of caps in typical applications that we use in guitar amp builds. I have assumed that dissipation is a measure of what we usually refer to as a "leaky cap", in that it can cause some big trouble in the destination tube should it be bad enough.

Thank you! Inquiring minds....
Best,
Phil Donovan

[martin manning]

I have assumed that dissipation is a measure of what we usually refer to as a "leaky cap", in that it can cause some big trouble in the destination tube should it be bad enough.

A leaky cap leaks DC, acting like a large value resistor. D-factor measures the losses in charging and discharging the cap, and depends on the dielectric type, frequency, and temperature. The dielectric type is a strong driver, with polypropylene being a decade or more lower than polyester. I'm not sure what that loss might mean to sound quality. I measured a few relatively new polyester caps with a B&K 879B LCR: 6PS, CDE, and M150 measured 0.003-0.004. A random ceramic disc measured 0.0003.

[pjd3]

Thanks for your input Martin.

We have Rohde & Scharz HM8118 prog LCR bridge.

I just measured some new caps from stock:
Orange drop SDE719 @ around .00017
Yellow multi-stacked ceramic @ around .007
and a tiny blue 1uF 10volt that I suspect is a tantalum (size vs value) @ around .018.

I surprised at the wide variation for all these new in stock caps but, this at least makes me think that the NOS caps I acquired aren't as out of field as I expected. But, this is a call to study up on where the dissipation value is derived from, and maybe gather a better perspective on what is a normal range for the various cap type and values based on what you said - dielectric, temp, frequency.
I measured all these caps at 1Khz, 1volt.

Thanks Martin.
Best,
Phil

[martin manning]

Those values look typical. Note 719 is polypropylene, and accordingly has a low D-factor. Here's a good general info doc on film caps: https://www.vishay.com/docs/26033/gentechinfofilm.pdf