I'm a newbie to this reflector so I have no idea how long this discussion
about Centurian idle current has been going on.
Let me add a few comments....
I have a Centurian (purchased new) which is now almost 5 years old. When I
received it I found that it had NO idling plate current. Discussions with
Ten-Tec indicated that the 2N3055 bias pass transistor was probably
defective. While that transistor is readily available at Radio Shack,
Ten-Tec sent me the need parts and a "modification" called a "Tube Bias
Cutoff Modification". This kit consisted of a replacement zener diode, an
MPS-U01 transistor and some other small components.
The explanation, on the instruction sheet said:
"The purpose of this modification is to turn off the tube bias while in
standby or receive mode. A few owners who had previous experience with
amplifiers from other manufacturers, noticed that we biased the tubes in
standby. Although this caused no performance problems, it was different
from what they had grown accustomed to."
The modification was for units manufactured before 3/2/92 and affected
several series of serial numbers.
Of note too, is that they changed the bias zener reference diode from a
1N756A to a 1N5344B .
While it would appear that the original writer had a problem too, and that
his amplifier was not working as Ten-Tec had intended; it appears from the
thread that the base cause had not been addressed and that the
correspondents were attempting to rectify a "design problem" that never
existed.
Those are my two cents worth....
73 - Ben, K2BF
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