[TenTec] 1999 Centurion amplifier - grid goes negative/output goes to zero

[Mike Schatzberg]

Also, if there was a short, the plate choke could be open and you will not see high voltage on the plate voltage metering.  Or perhaps a glitch resister opened. 

Did you look at the plate idling current without drive while keyed up and cutoff bias removed?  What was the current?

73,

Mike
W2AJI 



Sent from my iPhone

> On Mar 9, 2018, at 3:56 PM, Ken Brown <kenradiobrown at gmail.com> wrote:
> 
> Don't do that for a long time. The output matching network is designed for
> the plate impedance of two tubes in parallel, which is one half the
> impedance of only one tube. The variable capacitors in the Pi network
> probably have enough adjustment range to work at either impedance on the
> higher bands, but maybe not on the lower bands.
> 
> DE N6KB
> 
> On Fri, Mar 9, 2018 at 8:58 AM, Mike Schatzberg <
> cherokeehillfarm at earthlink.net> wrote:
> 
>> You can remove one tube, greatly reduce drive, and see if there is any
>> output. Make sure the anode cap from the removed tube is clear of
>> everything near it and not shorted. Replace all safety screening.
>> 
>> You can test both tubes, one at a time.
>> 
>> 73,
>> 
>> Mike
>> W2AJI
>> 
>> Sent from my iPhone
>> 
>>> On Mar 9, 2018, at 12:48 PM, Stan Gammons <s_gammons at charter.net> wrote:
>>> 
>>> Sounds like one of tubes shorted. If they are still under warranty, I'd
>> contact RF Parts and see what they say.  They replaced a tube I had that
>> shorted.
>>> 
>>> 
>>> 73
>>> 
>>> Stan
>>> KM4HQE
>>> 
>>> 
>>>> On March 9, 2018 11:11:45 AM CST, Bob  <w3hkk at roadrunner.com> wrote:
>>>> Bought this  used  from an estate sale in 2014.  Worked great for 3
>>>> yrs. Then a tube short blew a fuse.  Replaced both finals  and all was
>>>> well until a few months ago. The  amp  worked well for a few
>>>> transmissions, then the output went to zero.  After a few  cycles of
>>>> this I noticed the grid current which rested at zero began to migrate
>>>> negative.  As it   got worse, the output dropped to nil.
>>>> 
>>>> One suggestion was that one of my new tubes  ( from RF parts)   is
>>>> failing.  Another was  a possible problem in the AGC circuit.
>>>> 
>>>> Other suggestions?  Also, I may need  a repair tech and don’t want to
>>>> ship the amp, so someone in Ohio or driving distance from central OH
>>>> would  be a plus.
>>>> 
>>>> Thanks.
>>>> 
>>>> Sent from Mail for Windows 10
>>>> 
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