Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on October 25, 2011, 01:18:07 pm

Title: Capacitor Value?
Post by: plexi50 on October 25, 2011, 01:18:07 pm

I have a cap that is leaking DC voltage.  What do you think is the value of the cap pictured below?  Looks like 15 nano farad but it has 500 next to it.  I am not sure. This may not be an american made cap

I am assuming it is leaking because i am getting a small voltage on the other side of it

Title: Re: Capacitor Value?
Post by: FYL on October 25, 2011, 02:45:33 pm

Looks like a mica, an old poly or a weird ceramics.

There are three color bands, could be the old color code, used until the '90s or so. Yellow = 4, White = 9 if colors are correct on a ca. 1988 cap seen in quite low res on a laptop. 49 E 4 pf = 49 000 pF = 49 nF doesn't click as a standard value. Ditto if yellow isn't yellow but faded orange or brown.

So let's consider the markings. The inverted U could be a n, if so in European notation n15 = 0.15 nF = 150 pF. 500 could be the working voltage, quite strange in a silicon-based amp but pretty normal if the cap is a mica.

So I'd venture an educated guess : 0.15 nF / 500 V mica cap.

Now remove the offending cap and measure it... Even if it's leaky, you'll be able to measure it's capacitance.

Title: Re: Capacitor Value?
Post by: sluckey on October 25, 2011, 02:55:02 pm

Quote

I have a cap that is leaking DC voltage

How do you know that? Have you disconnected one end of the cap and actually measured a dc voltage on the disconnected end?

Or do you simply measure a voltage on each lead of the cap? This is absolutely normal and quite common.

Title: Re: Capacitor Value?
Post by: plexi50 on October 25, 2011, 04:12:06 pm

Thanks you all. I was thinking 15 nana 500 V but better to ask. Steve i lifted one end of it off the circuit board and it is showing near 1 volt. I am thinking to hard on this Greek amplifier im dead set on fixing

Title: Re: Capacitor Value?
Post by: PRR on October 25, 2011, 08:37:22 pm

It's not a tube amp. It would be quite common for there to be voltage on both sides.

Title: Re: Capacitor Value?
Post by: stratele52 on October 26, 2011, 03:41:41 am

It look to be 15 nanofarad = 0.015 microfarad at  500 volts , but I don't think you need 500 volts capacitor