Sent from my iPhone
> On Feb 21, 2017, at 7:45 PM, Jim Thomson <jim.thom@telus.net> wrote:
>
> Date: Tue, 21 Feb 2017 14:24:53 -0700
> From: MU 4CX250B <4cx250b@miamioh.edu>
> To: Bill Turner <dezrat@outlook.com>
> Cc: Amps group <amps@contesting.com>
> Subject: Re: [Amps] Checking Filament Voltage
>
> The simplest solution for amps with separate filament xfmrs is
> probably to install an inrush current limiter in series with the
> xfmr's primary winding. These look like disc capacitors and cost about
> a dollar. I use them frequently on any circuit that has a initial
> surge current, and a constant load current in equilibrium.
>
> Probably the easiest amplifier to install one in is the drake L4B. I
> removed the jumper on a terminal strip and replaced it with the
> current limiter. Took five minutes, most of which was spent removing
> the screws on the bottom cover.
> 73,
> Jim w8zr
>
>
> ## watch out. They run HOT in normal operation, with a normal constant
> load.
> Which is all fine, provided the inrush current limiter is not in the airflow
> of any blower.
> If it gets air blown onto it, its resistance will start to climb = bad news.
Very good point, Jim. Yes, ICLs run hot and must be kept out of a
cooling airflow. I normally do not shorten the leads to the ICL, and
insulate the leads with teflon tubing. I position the ICL so that it
is suspended by its leads (about an inch on each lead) and not
adjacent to other components.
My Fluke 87-5 has a peak reading feature, so in evaluating the effect
of the ICL, I replace the fuse (if one is in the primary xfmr circuit)
with a 1ohm resistor and measure the peak current before and after
installing the ICL. It's also good to measure the steady-state current
after the ICL has been on awhile. The specific device has to be
selected carefully.
73,
Jim w8zr
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