OWNER’S MANUAL MODEL ZP3 REV. DATE 2/2016
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VOLTAGE REGULATOR TUBE
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The OA3 tube is also known as a VR tube (Voltage Regulator) and is sometimes called
a “glow tube” because of the rich way that it glows during operation. These tubes are
what’s called “New Old Stock” meaning that they are new tubes manufactured
sometime in the 1950’s ~ 1980’s.
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While no longer made, there are many still floating around on the planet. They can be
found at your favorite tube suppliers, and on ebay.. Of course DECWARE will always
have top grade and tested OA3 tubes on hand for our customers. There is little fear of
running out of these tubes because few if any other manufactures use them. Decware
tube gear is one of the precious few to use tube regulation in it’s products.
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The OA3 tube does not get hot in a ZP3 so it can be touched during operation. Since
current passing through the tube is what “fires” it causing the glow you see, the tube
make flicker on and off several times on start up, or on shut down, or on both. This is
normal. Once this tube has a steady glow to it, high voltage is available to the audio
circuit.
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If you can not get an OA3 to glow it either means it is bad, or the rectifier tube has
failed. Since the rectifier tube supplies the high voltage to the OA3, the OA3 can not
glow unless the rectifier tube is working properly.
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It takes an OA3 tube around 20 minutes to fully stabilize. This means that at around the
20 minute mark the sound of the ZP3 can elevate even further.
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RECTIFIER TUBE
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The ZP3 is usually shipped with a hand selected 5U4G rectifier tube. Alternately you
may use a 5AR4 or a 5Y3GT with good results. The difference between a 5U4G and a
5YGT is a difference in high voltage of about 30 volts which is enough to effect the
sound, so experimenting with different rectifier tubes can further refine the voicing of
your ZP3.
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TECH NOTE: The first capacitor the rectifier tube see’s is a 47uf 500V
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