Message: 1
Date: Thu, 23 Jun 2016 16:41:50 -0400
From: Floyd Sense <k8ac@k8ac.net>
To: tentec@contesting.com
Subject: [TenTec] Fwd: Tentec Centurion bias question
Message-ID: <245abbbe-16ab-8563-99d9-1114f0ed13ce@k8ac.net>
Content-Type: text/plain; charset=utf-8; format=flowed
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
------------------------------
Message: 2
Date: Thu, 23 Jun 2016 14:58:05 -0700
From: "A R" <raf_3@msn.com>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] Fwd: Tentec Centurion bias question
Message-ID: <BAY173-DS8719B3CD188059C21C08FDC2D0@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"
Floyd,
I'm guessing that the 100ma Ip is in both the standby and operate modes?
Same condition experienced here on my Centurion was corrected by replacing bias
transistor Q1 on the FILAMENT-AC board. Leads for that transistor are accessible. Check
for collector to emitter short. I replaced the failed MJ15001 Q1 with a JAN
2N3055...problem solved. You might check the archives for "Cenurion 422b
troubleshooting help" thread on 3/3/2016 for details on the Q1 failure cause.
Good luck,
Allen--W7GIF