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

[Bob]

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.

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