Bottlehead Forum

General Category => General Discussion => Topic started by: aragorn723 on March 17, 2014, 04:18:50 PM

Title: coupling cap vendor
Post by: aragorn723 on March 17, 2014, 04:18:50 PM

Hi,

I'm looking to buy some paper in oil capacitors to use as coupling caps in the Quickie.  Is tubes-store.com a reputable site to deal with?  These are the caps:

http://tubes-store.com/product_info.php?cPath=35_41_84&products_id=525

Is a 5% tolerance good?  Should I be worried about getting a lower tolerance?  Thanks,

Dave

Title: Re: coupling cap vendor
Post by: galyons on March 17, 2014, 04:26:36 PM

Never done business with that vendor.  Mostly I bought on the 'Bay.  Russky caps are generally 10% and I buy enough to justify postage and then match pairs.  K40's and K75's seem to hold their values well.  5% would be even better!!

Cheers,
Geay

Title: Re: coupling cap vendor
Post by: Paul Birkeland on March 17, 2014, 04:38:52 PM

I haven't used that vendor, though I will say that eBay is pretty reliable.

Tolerance is incredibly unimportant in the Quickie.

-PB

Title: Re: coupling cap vendor
Post by: aragorn723 on March 17, 2014, 04:45:59 PM

why is tolerance unimportant?

Dave

Title: Re: coupling cap vendor
Post by: aragorn723 on March 17, 2014, 04:48:39 PM

Quote from: galyons on March 17, 2014, 04:26:36 PM

Never done business with that vendor.  Mostly I bought on the 'Bay.  Russky caps are generally 10% and I buy enough to justify postage and then match pairs.  K40's and K75's seem to hold their values well.  5% would be even better!!

Cheers,
Geay

How do you match capacitors?

Dave

Title: Re: coupling cap vendor
Post by: galyons on March 17, 2014, 05:19:37 PM

Nothing fancy! I measure and match the capacitance.  I have a capacitance meter.  But my DMM also has a pretty accurate capacitance function.

I always try to match inter-stage coupling and output caps pretty closely.  As long as the caps are fairly closely matched, marked tolerance can be ignored.  The tolerance just gives the manufacturer's allowable margin of error within a run lot.  Not to important for onesy/twosies!! But I always like closer quality control!

Cheers,
Geary

Title: Re: coupling cap vendor
Post by: Grainger49 on March 18, 2014, 12:02:58 AM

I received 4 KK POI 2uF@200V yesterday.  They were all accurate to the first zero.  They measured 2.01, 2.02, 2.04 and 2.06.

I haven't used that vendor either.  But have never had a problem ordering from the former USSR. 

I wouldn't order from Ukraine right now.

Title: Re: coupling cap vendor
Post by: Paul Birkeland on March 18, 2014, 09:21:11 AM

Quote from: aragorn723 on March 17, 2014, 04:45:59 PM

why is tolerance unimportant?

Dave

Let's say that a 2.0uF cap has +/- 50% tolerance and is driving a 10K load, and that the pair of capacitors are as poorly mismatched as possible.

The outcome of this worst case scenario is that one channel will be -3dB at 5Hz, and the other will be -3dB at 15Hz.

Do note that capacitors in equalization circuits will require tight tolerances, however. 

Title: Re: coupling cap vendor
Post by: aragorn723 on March 18, 2014, 11:05:47 AM

a difference of 10hz isn't much, wasn't sure how the math worked out   8)  I have an amp with a 10K input impedance and my quickie has the PJCCS, would changing the value of the output capacitor make them match together better?  Thanks,

Dave