[AMPS] Smallest practical 1.5KW 20uH coil

[Harald Garberg Gule]

Hi all

I have been following this tread with great interest. I have also been
thinking
abouth using toroids in the tank cirkuit, as they seem to offer at least
space
saving whenever that is a problem.
For me it would be more expensive to use , since I have to buy them,
but have enough surplus of both nice L's and C's.

I must admit I was becoming afraid at using toroids after a few initial
comments to this tread. I was getting really confused since successful
producers
have been using them a long time both for commercial and
amateur service and suddenly it almost appeared a no-no.
If the producers save money thus giving them a better profit,
and hopefully giving their customers good value it's all right with me.

Thus I appreciate the the helpful ideas put forward recently.

For helpful hints on making toroids you can find a practical approach
article in Ham Radio, August 85 by Robert E Bloom, W6YUY

 Design a toroidal tank circuit for your vacuum tube amplifier.


Harald, LA6LHA



-----Original Message-----
From: owner-amps@contesting.com [mailto:owner-amps@contesting.com]On
Behalf Of Richard W. Ehrhorn
Sent: 25. januar 2000 23:36
To: 'wc6w@juno.com'; amps@contesting.com
Subject: RE: [AMPS] Smallest practical 1.5KW 20uH coil



Hi Marv...

I'd go with the stacked T200-2 cores - Before winding, you can give
yourself a bigger insulation margin of safety by wrapping the core stack
with a couple of layers of Scotch/3M #25 fiberglas tape (can someone
confirm that #25 is the right designation?) .

Don't know how you calculated it, but loss at 1.8-2.0 MHz should be almost
unmeasurably small - anything over roughly 15W loss (1% or 0.04 dB at 1.5
kW) would cause the toroid to run quite hot.  But in fact literally
thousands of commercial amps have for decades used approximately the toroid
inductor you describe without problems.

Good luck!

73,      Dick    W0ID


-----Original Message-----
From:	Radio WC6W [SMTP:wc6w@juno.com]
Sent:	Monday, January 24, 2000 11:11 PM
To:	amps@contesting.com
Subject:	[AMPS] Smallest practical 1.5KW 20uH coil


Hello to the group,
  I'm contemplating some alternative designs for a 20uH,160M "padder",
coil, to be switched in following the Pi-net roller coil in my 4-400A amp
under construction.

  The "typical" 3" long by 3" diameter section of B&W stock, including
reasonable clearance to adjacent components, would take up a bit too much
space in this instance.

  I thought of winding 20 turns of #10 teflon on four stacked
(Micrometals / Amidon) T200-2 iron powder toroids but, that also gets to
be rather large (2.25" diameter by 2.5" long) and is surprisingly lossy,
if I did the math correctly.

  I'm now considering a short solenoid cross section wound in the form of
two adjacent spirals (one spiraling into the center, the other out)
fabricated from .375 by .07 silver plated copper ribbon.   Sixteen turns,
8 in each spiral, in a 3" diameter by just under 1" thick form factor
should provide the requisite inductance.  I'll just slip some thin strips
of fiberglass between the turns to keep them properly spaced.  The only
drawback that I perceive in employing this geometry is the somewhat
higher than usual inter-turn capacitance but, this part is only for use
on 160M.

 Comments, suggestions, alternative ideas???  but, please no
superconductors! :-)

73,
  Marv WC6W











*

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FAQ on WWW:               http://www.contesting.com/ampsfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm