PSN-L Email List Message

Subject: Obsolete I.C. needed
From: "Al Allworth" allworth@..............
Date: Wed, 12 Jul 2000 13:10:47 -0700

Hi All,

Do any of you know where one could find a Motorola or equivalent MC3420
or MC3520? I know there are some suppliers of obsolete I.C.s but have
lost access to the sources I used before retiring. I need one for a power

                            Thanks,       Al

                     Al  Allworth        W7PXX

On the Beautiful Southern Oregon Coast

----- Original Message -----
From: "S-T Morrissey" 
Sent: Wednesday, July 12, 2000 12:44 PM
Subject: constant voltage transformers

> Regarding constant voltage transformers, or CVTs.
> I have been using them for over 30 years, and have always found
> a sinewave output. There are some better designs that use a
> larger high voltage AC capacitor for the resonant circuit that
> are "harmonic neutralized" and regulate to 1% over a +,- 20%
> input change. These cost about 10% to 20% more than the 3% regulation
> "line conditioners", which DO put out a sinewave, but with higher
> distortion. The very nature of CVT design is that it is a true
> transformer (total isolation of the input from the output), that
> only passes a sinewave to the output winding at the resonant
> frequency of the high voltage secondary/capacitor circuit.
> If you play with one with a variac (variable transformer) input,
> you can see this: as you increase the input, there is little
> output until there is enough voltage (about 45 volts AC) to resonant
> the high voltage secondary, at which point the output jumps to within
> a few percent of the regulated level. As you drop the input voltage,
> to as low as 20 VAC, the output remains near 110V as long as the
> transformer resonants (test with a moderate load, like a lightbulb).
> SOLA is a major manufacturer, and they claim that their standard
> conditioners (MCR series) will output a sinewave with 3% THD (total
> harmonic distortion) with a square wave input. I use a 120 watt CVT
> with my large frequency controlled converter in my field van to
> convert the square wave to a sine wave for electronic loads. This
> is similar to common marine use for AC operated electronics.
> Since CVTs are passive, they last a long time; the main problem being
> the high operating temperature of the transformer core that eventually
> cooks the insulation, and the high voltage (660 volt) AC capacitors that
> eventually fail causing a voltage drop. The capacitors are replaceable.
> Since CVTs ONLY pass a completely isolated sinewave, I have always
> used them as a primary protection of the AC line from lightning. They
> always work, except in one case when the lightning arced thruout the
> case to the secondary line. I have had one at a shared tower facility
> where lightning has frequently smoked the varistor-based line protection
> of the other equipment, while the seismic station and transmitter were
> never harmed. They are an expensive ($350 for 250 watts) but permanent
> solution for protecting AC loads.
> Regards,
> Sean-Thomas
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Larry Cochrane <cochrane@..............>