Oh yes!
It was used in the series heated filament string in tube TV ages ago.
At the time it was called a thermistor!!
What you were thinking about was the VDR, a non linear resistor that was
used in TV sets to provide some measure of voltage stabilization in the
vertical and horizontal oscillators. It behaved something like a zener diode
but was intended for currents in the tens of mA range.
Alex 4Z5KS
Alex 4Z5KS
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Jim Garland
Sent: Sunday, September 15, 2013 10:55 PM
To: amps@contesting.com
Subject: Re: [Amps] Rectifier equilization?
Although it is made by GE, I believe the CL-90 is not a surge
suppressor, but an inrush current limiter. It's probably an MOV of some
sort, but not the type normally used for surge suppression. When cold, the
device has a high resistance, which limits inrush current. It rapidly heats
up (a few seconds) and the resistance drops, becoming negligible in steady
state. The CL-90 is rated at 120 ohms cold and 2 ohms steady state. Steady
state current should be roughly 1A for this device.
I use this family of devices for filament inrush protection (e.g.,
in the primary of an Drake L4-B filament transformer), in the power supply
of small transmitters (e.g., Johnson Ranger), boatanchor receivers (Collins
51S-1), and so forth.. They normally run quite hot, so I take care to
position them in the clear and I don't shorten the leads. I use a bit of
teflon tubing to insulate the leads. Although they have to be sized properly
for the particular application, they're very handy devices, and dirt cheap
protection.
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Carl
> Sent: Sunday, September 15, 2013 12:14 PM
> To: Ian White; amps@contesting.com
> Subject: Re: [Amps] Rectifier equilization?
>
>
>
> > >The problem with MOV's is they have a narrow current range where
> > >they
> >>are most efficient and either side of that the internal resistance
> >>and
> > heat
> >>goes up.
> >>
> >>Carl
> >>KM1H
> >>
> > Please could you expand on that, Carl? MOVs are non-conducting
> > unless they are actually limiting a surge, so I'm not sure how
> > internal resistance, heat and "efficiency" (in the normal
> > engineering sense of that word) come into it.
>
>
> My error, I had them confused with the GE surge suppressors many use
> and have trouble with, the CL-90 for instance.
> MOV is a GE registered trademark BTW.
>
>
> >
> >> They also have a finite life.
> >
> > MOVs are sacrificial components. Their mission in life is to 'take a
> > bullet' from line surges to protect other, more valuable components
> > downstream. But their working life is closely related to the total
> > amount of energy they have absorbed... and as well as damage due to
> > large surges, there is also damage from long-term exposure to the
> > much larger numbers of small surges.
>
> Already well covered in the literature.
>
> > In a normal shack PA, the working life of an MOV can be greatly
> > extended by placing the MOV on the downstream side of the main power
> > switch, so it isn't exposed to any surges unless the amp is in use.
>
> IMO placing them after the switch is the normal way of installing them.
The
> other option is as part of an external line filter/Spike suppressor
> which
is
> popular with the receiving end but those have proven to be prone to
failure
> resulting in smoke when least expected.
>
> > Also don't forget the benefits of a mains filter. As well as
> > filtering high-frequency impulses coming backward out of the power
> > supply, the filter will reflect most of the high-frequency
> > components of any incoming surges.
> >
> > 73 from Ian GM3SEK
>
> Ive been using HB line filters for decades on everything from home
> electronics, vintage radios scattered around the house, vintage and
> modern ham gear including amps, test equipment, etc. It started when I
> built a
very
> competitive contest station in the 80's and wanted to keep family and
> neighbors out of my hair. It grew once consumer electronics became a
scourge
> and I became obsessed with a clean AC line as well as what was coming
> in
on
> feedlines and control cables.
>
> Large full house MOV's are installed in the mains box right after the
> 200A breaker.
>
> Carl
> KM1H
>
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