T O R I I J R O W N E R S M A N U A L
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Additionally, it should be understood that an OA3 tube takes approximately 20~22
minutes to fully stabilize. During this period it is advised that you keep the amplifier on,
for at least 20 minutes. Following this regimen will ensure your OA3 tube lasts for many
years, if not the life of your amplifier.
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The OA3 is also known as a VR75. It is a vacuum diode that has a 75 volt drop across
it’s plate and cathode. This could btw., easily be done with a simple resistor, however
using the rare vacuum diode tube we gain 20 times more ripple (hum) reduction and
complete isolation from the power supply so that the power that feeds the input stage
is nearly perfect like a battery. This makes possible the jet black backgrounds you
hear that are essential to underpin the amazing layering that this amp projects.
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It should be mentioned that the voltage drop across the OA3 determines the DC
voltage that feeds the input stage. With an oA3, the input stage performs well with low
distortion and the maximum amount of clean gain. Occasionally when the full 20 watts
of the amplifier are not required, experimentation with VR90, VR150 tubes have proven
interesting. Since these tubes create a higher voltage drop, they also increase
isolation making them more like a pure battery. The increased voltage drop, lowers the
gain of the tube and increase the distortion of the tube once that gain window is
pushed. This results in a different clipping character and overall different sound to the
amplifier based on the particular input tube that is used. For example, you may drop
the power from 20 watts to 6 or 8 watts but within that zone realize better sound that
consequently better serves a high efficiency horn loaded speaker system.
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The OA3 is in series between the power supply and the input stage meaning it will also
become a fuse for the input stage should the input tube exhibit a catastrophic failure or
short. In that case, the OA3 will likely flash and go dark killing all power to the input
stage and saving the internal parts in the amplifier from excessive stress. There are no
heat producing parts internally therefor nothing internally in the amplifier fails unless
the fuse was tampered with.
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It is also worth mentioning that the OA3 tube does not get hot in this amplifier, but it
does get very warm. The other tubes in the amplifier by comparison can NOT be
touched. Temperature of the OA3 reaches around 105 degrees F. The EL34’s are
nearly
300 degrees F
. The 5U4 typically runs at
220 degrees F
(100 degrees
Centigrade)
.
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While we’re talking about temperatures, it should be noted that overall heat was a
careful part of the design, not an after effect of the design. Heat will be discussed in
it’s own section of the manual.
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Decware High Fidelity Engineering Co., East Peoria IL, USA www.decware.com
