pico farad scale caps

[llama]

Hi all,

I have two Silver mica Picofarad caps that are the only ones i have and measure way high with my DMM (set on capacitance).

I have a 250p that measures 520p, and a 47p that measure 200p. 

Before i go further, is it likely my meter is reading false?  It's specified to go down to 10p (harbor freight dmm).

the 47p is for a gain pot  bleed and the 520p is for the treble cap in the tone stack.  Are these value differences going to make a big difference?

Thanks!

[SILVERGUN]

Before i go further, is it likely my meter is reading false?  It's specified to go down to 10p (harbor freight dmm).

Yes, anything from Harbor Freight is suspect....the leads of your meter have an inherent capacitance before they are even connected to a cap....
My Fluke meter got a little squirly when reading small values like that so I imagine you're not getting a true reading with that meter

I bought this just for that pupose and it has been dead on: (it has 2 holes where you can insert the leads of a radial leaded cap, and two short test clips for axials)
http://www.newark.com/tenma/72-8150/capacitance-meter-with-resistance/dp/41M0998

Just for the record,,,it says the range only goes down to 200pf, but I've measured down to 10pf with precice readings....the lowest manual range setting is 200pf

[Willabe]

the 47p is for a gain pot  bleed and the 520p is for the treble cap in the tone stack.  Are these value differences going to make a big difference?

Yes, those values are way different (IF they are correct readings) and will change the amps sound.


                  Brad     

[plexi50]

What amp are you working on?

[llama]

Thanks again, Silvergun.  That was my thought.  I just bought these caps, so i suspect my methods.  I just got them from Doug, he replied quickly to my mail, and mentioned that they are usually really close to the published value.  I'll bring them over to your shop when i stop by.

Sorry that I did not mention what I'm working on.  It's a custom amp with a 5879 tube. 

feel free to see the schematic  - C6 and C11 are the caps in question.

Thanks Willabe and Plexi50!!

[EL34]

The Silver mica caps you bought from me are + or - 5% tolerance

47p can be + or - 2.35p
250p cab be + or - 12.5p

I suspect the meter or method because out of 1000's of these, no one has ever emailed me about the values.

Meter leads have capacitance
Your fingers have capacitance

I would just install them and forget about trying to nail down an exact value

[llama]

Doug,

I'm sure your right.  Sorry if my NOOB was showing....

Thanks for the quick response!

[Ed_Chambley]

Never got one from Doug that was even close to 5% drift.  I have a meter that they insert into.  Best this way.  My problem is not measuring them, it is seeing them.