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The following is extracted from Electronic Design Magazine, May 15, 1995.
High-speed programmable amplifier/power supply
finally forsakes the venerable vacuum tube!
An article by Dave Maliniak.
Decades ago, the solid-state revolution in the electronics industry began sweeping out what some older engineers endearingly
refer to as
"fire bottles" or "hollow state devices" -- in other words, vacuum tubes. That's probably not news to anyone. What
may be news to some, however, is that the revolution isn't over. With some reluctance, one of the last volume users of vacuum
tubes other than CRTs and high end audio applications has come up with a solid state replacement for a tube that had, until
recently, been thought irreplaceable.
In its
Bipolar operational power supply (BOP) line of high voltage, high power supplies/amplifiers, Kepco, Inc., of
Flushing,
NY, has long used the type 8068 tube as a series-pass control. Now, with that tube becoming very hard to obtain, the company
has devised an FET based substitute. The replacement not only replaces a bank of eight type 8068 vacuum tubes in new production
BOP, but is available as a drop-in replacement for existing units. This is an important consideration to support the large
installed-base of BOP.
One consideration that worried the designers at Kepco was dynamic performance. It is very good news, indeed, that the new
FET-based BOP meets and even exceeds the bandwidth and slew-rate performance of the older tube based design.
A spokesman for Kepco said "The tubes are going away, but not because we wanted them to. If we had our way we'd have probably
continued using them. In the world of high voltage control it's pretty hard to beat something
that's at home with 4500 volts on its plate. If it does zap over, it recovers fine. If it's overloaded, it just glows blue.
It's a wonderfully forgiving device. And, I'll miss the built-in pilot light."
Editor's Note:
Kepco has been shipping FET based BOP since early in the year and customer acceptance and performance has been terrific. The
vacuum tube versions are entirely phased out now.
The high voltage BOP were not the only Kepco models to employ the 8068 tube. They are used in the BHK and APH product lines
too. Programs are underway to redesign both of these groups to use FETs. Unlike the BOP, however, it will not be just a drop-in
replacement. Kepco will design completely new products with microprocessor control, digital displays and built-in GPIB. Look
for new product announcements early in 1996.
The APH are 20 Watt unipolar power supplies rated 0-500V, 0-1000V and 0-2000V.
The BHK are 200 Watt unipolar power supplies rated 0-500V, 0-1000V and 0-2000V.
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Vol.6, No.1