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Re: [TenTec] Fwd: Tentec Centurion bias question

To: tentec@contesting.com
Subject: Re: [TenTec] Fwd: Tentec Centurion bias question
From: Carter Grabarczyk <k8vt@ameritech.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 23 Jun 2016 19:56:21 -0400
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
On 6/23/2016 4:41 PM, Floyd Sense wrote:
I recently acquired an early Centurion (serial 10A10221) from an SK's estate. The resting plate current, PTT not keyed, is around 100 ma and the 3-500ZGs have a nice orange plate glow. I had read in the archives that later changes resulted in a much lower resting plate current and set out to see what the current state of circuits is in this amp. ( Yes, I know that level of plate current is OK, but it generates considerable heat on the desk that I don't need.)

The amp has obviously been updated at some point as the Filament-AC board has the new bias circuitry and the QSK board is revision C. The Filament-AC board circuit as shown in the 10/94 rev C diagram agrees with the schematic. So, I'm guessing that I might have all the latest changes in regards to bias. The question is: Is the observed 100 ma resting plate current what others are seeing in the Centurion with the later bias changes? If that level is normal, I was thinking about maybe using the Ameritron ESB-1H board which would reduce the resting current to just about nothing with no excitation. Any thoughts? Tentec has not responded to an email on the subject.

73, Floyd - K8AC
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As I recall, the resting plate current should be close to zero. On my Filament-AC board, I had to replace the transistor two different times; for whatever reason, they were a bit notorious for failing. Before you do anything else, take a close look at that transistor, Q1, 2N3055. Also, according to the manual, the QSK board (81542) can cause a similar problem.

LETHAL voltages inside, be careful!!!

73,

Carter   K8VT

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