A sustained arc in a small glass fuse improperly used at 10 times or more
its rating is far from a rare occurance.
It gets downright dangerous when the glass breaks and the small arc becomes
a monster plasma arc searching for paths to ground.
Using a small wire as a HV fuse can also create a similar problem.
Carl
KM1H
----- Original Message -----
From: "Bryan Swadener" <bswadener@yahoo.com>
To: <amps@contesting.com>
Sent: Saturday, October 05, 2013 6:41 PM
Subject: Re: [Amps] 160M PI network Toroidal Coil
I might as well add my input...
My GS35b 160m monobander will use about 15uH fixed
and 16uH adjustable, to drive ~ 25 to 500 ohms.
The fixed inductor is 20T 10 AWG 19-strand silver-
plated copper wire (w/ PTFE insulation) on a Micrometals
T400-2D core. Core and wire losses should be naught.
I found two cores and the wire on ebay for a good price.
I used my spreadsheet calculator to determine the maximum
wire diameter, number of turns and length of wire needed. YMMV.
Mike, that's interesting about the fuse. At HV with
a 250V fuse, I would've expected a sustained arc.
vy 73,
Bryan WA7PRC
------------------------------
Date: Sat, 5 Oct 2013 13:10:21 -0500
From: Mike WØBTU
To: amps@contesting.com
Subject: Re: [Amps] 160M PI network Toroidal Coil
When I converted my SB-200 to a single-band 160m amp, I followed the
directions (more or less) at
http://pa0fri.home.xs4all.nl/Lineairs/SB200/sb200eng.htm#DESIGN . The
toroid was a single T-200-2 core with between 11t and 14t of #14 stranded
PTFE insulated wire, IIRC. The details are on that site. I got almost 800w
out on 160 CW.
I also used a large (>1600 pf) external variable loading cap to the output
with a UHF tee connector and a short length of RG-58C/U.
Some photos except for the toroid (on the bottom) and the added plate choke
are here:
http://www.w0btu.com/files/misc/SB-200/ . The extra filament choke and the
PA0FRI input mods are clearly visible in the first photo.
While you're at it, add the fuse and series 10 ohm 10w resistor to the HV
line. I used an ordinary 250 volt AGC 1 amp fuse. When I first replaced the
tubes, it blew a couple of times with nothing more than a silent blue flash.
73, Mike
http://www.w0btu.com/
------------------------------
Date: Sat, 05 Oct 2013 11:44:02 -0700
From: Paul Baldock
To: amps@contesting.com
Subject: Re: [Amps] 160M PI network Toroidal Coil
Thanks to every one on their suggestions. It seems that multiple
T200-2 cores are the most common.
- Paul
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