[TenTec] Centurion Trubleshooting help

[Frank Sweeney]

correction:

How do I measure the bias voltage?  Is it between ground and terminal K or
is it between connector *21* and Terminal K?


Ten Tec Centurion



Initial problem Description:  occasionally that on initial Turn on when
tuning the amp will not driving.  No Grid or Plate current, high swr back
to xcvr.  Gentle tap near relays fixed the problem.



Secondary problem description:

Within 2 weeks of daily use with initial problem the amp now exhibits about
10 mA grid current with no excitation, finals glowing and getting hot.  This
condition went un-noticed for approximately 10 minutes.



Trouble shooting:  1. DMM shows short of Q1 Bias in circuit, upon removing
Q1 (PITA) found Q1 and all other active parts to be ok in the bias circuit
Short still present and pulled tubes and found F-G short in one tube



Installed new 3-500



3rd problem description: the amp will not drive, No Plate current, No Grid
current High SWR back to the xcvr



Trouble shooting:  using external supply to power the QSK board, Relays are
switching,  Output relay when closed reduces received signal.  Input relay
is moving a signal from my signal generator through the input filters to
the cathodes as measured on my Oscilloscope.



The tubes are acting like they are biased into cutoff



Replaced ICs in QSK board even though the QSK board appeared to be working
correctly, added IC sockets and 15V transorbs while I had it apart.  Did
not fix problem



Bias resistors test good



Help what else can it be?

How do I measure the bias voltage?  Is it between ground and terminal K or
is it between connector 22 and Terminal K?



What voltage should I read at terminal K of the filament board during

1.      Stand-by

2.      Transmit



Thanks in advance for any help



73,

Frank K9IC