Question about parafeed caps

[adamct]

Can anybody here explain to me what the 0.1uf interstage caps do?

1. What is their purpose / function? How do they differ from coupling caps (which I believe exist to block DC from the outputs)?
2. How "audible" are they, as compared to the coupling caps, for example?
3. Lastly, what considerations go into selecting interstage caps from a technical perspective? The stock caps are metalized polypropylene.

Best regards,
Adam

[Grainger49]

The interstage caps keep the first stage's plate voltage off of the second stage's grid.  If the grid were higher voltage than the cathode the tube doesn't work well.

Yes, they are coupling caps.  The name "interstage" gives you the answer to where they are.

They are in the signal path.  But for some reason the final cap has more effect on the sound.  I don't know why, I just accept it.  Still I upgrade interstage caps, see below.

Since the plate of the first stage floats to the B+ at the output of the diodes at start-up they need to be high enough voltage.  The RC time constant is different than the output cap and interstage caps are most often 1/10 the size, or less, of the output caps.  Again, the signal goes through them and my first tweak on my Paramours was to change the interstage caps to KK Teflons.

[adamct]

Wow! Thanks for the quick and helpful response, Grainger.

Much appreciated,
Adam

[Grainger49]

I wanted to add this.  We had a poster who was looking at KK Teflons for his Paramours.  He saw that there was a considerable savings to buying a lot of them.  He put together a group buy, on an honor system only, and we all got a pair of 0.1uF 500V KK Teflons sent to us after they arrived.

A true sense of community.  Just had to add this.

[corndog71]

I found the interstage position to very much appreciate the better cap.  V-Cap TFTF works really well.  One of these days I want to try the CuTF version.  Just have to start saving for them.

[Grainger49]

Rob,

They make a difference that can be heard.  As for the Teflon V-Caps, they take either a good expendable income or good anesthesia to the price. 

[adamct]

Grainger,

I think there was a typo in your last post. I believe the word you were looking for is "euthanasia"*...

Best regards,
Adam




* Just kidding, of course...