[TenTec] Fwd: Tentec Centurion bias question

A R raf_3 at msn.com
Thu Jun 23 17:58:05 EDT 2016


   
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


----- Original Message ----- 

From: Floyd Sense<mailto:k8ac at k8ac.net> 

To: tentec at contesting.com<mailto:tentec at contesting.com> 

Sent: Thursday, June 23, 2016 1:41 PM

Subject: [TenTec] Fwd: Tentec Centurion bias question



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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