coupling cap vendor

[aragorn723]

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

[galyons]

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

[Paul Birkeland]

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

Tolerance is incredibly unimportant in the Quickie.

-PB

[aragorn723]

why is tolerance unimportant?

Dave

[aragorn723]

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

[galyons]

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

[Grainger49]

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.

[Paul Birkeland]

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. 

[aragorn723]

a difference of 10hz isn't much, wasn't sure how the math worked out     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