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Re: My parafeed 300B prototype and questions

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Paul Joppa

(P)

In Reply to: My parafeed 300B prototype and questions posted by Tanker on May 17, 2004 at 21:05:30:

Huh - I though I had posted, but it's not there now. Maybe I punched the wrong button.
Your hum is not from the power supply, which if built as shown should have about 1mV ripple. The 300B cathode hum vltage is 0.1 times the plate voltage, but mu is less than 4, so there must be a lot of hum at the grid also. Perhaps your plate chokes are too close to the power transformer? Hard to say; hum-busting is a pretty long and frustrating experience unless you get lucky. I wish you good luck!
C3 of 4uF works well with TFA-2004. Can't say about the others, maybe someone who has worked with that topology can comment?

Follow Ups:

What Type of Cap for Parafeed? - MikeT 06:25:40 05/23/04 (2)
Oiler? Solen? Other?
- Re: What Type of Cap for Parafeed? - Paul Joppa 11:51:24 05/23/04 (1)
  From another post on another subject:
  "I have no idea how different caps will sound (to you, in your system...) and to be honest, I wouldn't admit it if I did. When it comes to caps, you pays your money and takes your choice. I avoid the subject of cables too. :^)"
  People's reactions to caps vary a lot, and so far it appears that taste is the predominant criterion. There is virtually no consensus on what is best, and very little on sonic descriptions. To complicate things, PIO caps are said by some to sound less soft in parafeed applications than in interstage coupling applications.
  I have enough Scotch ancestry to use the cheaper alternatives when there is no clear preference, so I use Solens. But then, I also have not pursued studies to compare caps - I'd rather change the circuit to get an effect. I don't question the value of parts selection, it just interests me less.
  FWIW (not much!) here's my summary of what I hear others saying:
  Mylar sounds muddy
  Polypropylene sounds plasticky
  Teflon sounds buttery but brittle and edgy
  Oil sounds smooth and euphonic
  Construction details are said to have a big effect, confusing the issue. Steel leads are bad, foil instead of metalization is good, winding tension counts, etc etc.
  - Thanks For The Info (nt) - MikeT 07:55:48 05/24/04 (0)
Paul! is the 1mV ripple mentioned regarding to at the 300B plate or - Tanker 05:12:14 05/20/04 (0)
at the cathode end? Also if you look at the picture, the plate choke is really far away from the power tranny. The power tranny is a military potted one.
Using Duncan model, the ripple should be much much less than 2.5V at the plate, but not really sure why I get that much.

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