[TenTec] Fwd: Tentec Centurion bias question

[Carter Grabarczyk]

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