[TenTec] Tentec Centurion bias question

[Floyd Sense]

The 100 ma was the same in standby or operate.  I've found one problem 
so far - the MJ15001 was OK, but the transistor that drives it on the 
Filament - AC board was shorted.  Normally, that transistor controls the 
2N3055 with a signal from the QSK board. That transistor stage was not 
present on the original Filament-AC board.   The transistor driving that 
line on the QSK board is OK, so I've replaced the one on the Filament- 
AC board and that may solve the problem.  It will be a couple of days 
before I know as I'm waiting on another part that was  blown on another 
board.


> Message: 1
> Date: Thu, 23 Jun 2016 16:41:50 -0400
> From: Floyd Sense <k8ac at k8ac.net>
> To: tentec at contesting.com
> Subject: [TenTec] Fwd: Tentec Centurion bias question
> Message-ID: <245abbbe-16ab-8563-99d9-1114f0ed13ce at 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 at msn.com>
> To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
> Subject: Re: [TenTec] Fwd: Tentec Centurion bias question
> Message-ID: <BAY173-DS8719B3CD188059C21C08FDC2D0 at 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
>
>
>