Thanks Floyd and Gary,
I should have mentioned that this is a Black face Centurion Purchased in
2011.
Problem is now resolved. There was 2 things I repaired last night before I
turned off the lights
1. C11 on the HV board was hanging, I supect that it never was solder from
the factory, I seriously doubt that was the issue
2. reflowed solder on Q1 (I believe I had a cold solder connection)
for future reference, Bias voltage at K is 28V unkeyed, 8.5V Keyed
Note to self: If grid current is flowing with no excitation, pull tubes
first and then check Q1 to see if short is removed. (Not wanting to
believe that I was going to spend $100+ on a 3-500Z I went the cheap route
and pulled Q1.) Had I not removed Q1 on day 1 I could have saved myself
several hours.
However, what a great learning experience.
1. I now understand how every circuit in the Centurion works.
2. Ten-Tec did not update their schematics for instance my schematic in
the supplied manual shows a 2N3055, I have a MJ15001. There are various
resistors on the HV supply that have been changed while others removed
3. Connector 21 on the filament board is connector 3 on the HV board and
is marked Standby/Op switch on the schematic
Frank
On Thu, Apr 26, 2018 at 10:23 PM, Frank Sweeney <k9ic.ars@gmail.com> wrote:
> Ten Tec Centurion
>
>
>
> Initial problem Description: occasionally on initial Turn, amp will not
> drive 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, check
> switching, 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. Retest Bias circuit
> components al test OK
>
>
>
> 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
>
>
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