Hi Al,

I show some (20)  in my personal stock.  I will have to search as I have never
resorted them after my move to Colorado.  I will look in the next few days and
get back to you.

Raul Alvarez

Al Allworth wrote:

> 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
> supply.
>
>                             Thanks,       Al
> _______________________________
>
>                      Al  Allworth        W7PXX
>
> On the Beautiful Southern Oregon Coast
>
> ________________________________
> ----- Original Message -----
> From: "S-T Morrissey" 
> To: 
> 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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>
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