[TenTec] Centurion Amplifier draws negative grid current-help requested

W3HKK at roadrunner.com W3HKK at roadrunner.com
Fri Feb 12 09:29:35 EST 2021

This may or may not help, but here's my story. My 23 yo Centurion
worked like a charm for 5 years after I bought it used, 10 yrs ago.

Then one day the grid started going negative. I had a local tech look
at it...twice. The first time we changed out the original tubes. A few
months later a similar problem began and he repaired/replaced the bias
transistor...and I believe a grid resistor. (The amp warmed up ok then
the grid meter would slowly begin to crawl its way negative as the amp
idled.) But because he was a good tech with good prices, but took 3-4
months to fit ham gear in between his normal police/fire department
repair work, I bought a new ACOM1000 for my birthday, so as not not to
miss a couple of big contests.

 FWIW the new amp had problems a year later with reduced output. Turns
out the finals in it were defective. The factory rep replaced the
finals and sent it back. Soon it began tripping out the safety
circuit. Sent it back in and he replaced the finals he had put in at
no cost. Since then Ive had full output and all is well. My point:
Finals have caused 3 of my 4 amp problems - two on the Centurion and 2
on the ACOM. Apparently it is not unusual for the ACOM1000 finals to
be damaged in shipment...even to or from their tech repair center.!) 

Meanwhile I eventually got the Centurion amp back, working well. It is
now my backup. 

I will say this. Not many amps are built better, are more attractive,
and have smoother tuning than the Centurion. Had it not been for those
two issues and the slow local repair service, Id still be using it
today. Had no other complaints. 

	-----------------------------------------From: "Dave’s" 
To: tentec at contesting.com
Sent: Friday February 12 2021 8:44:43AM
Subject: [TenTec] Centurion Amplifier draws negative grid current-help

 Hi all,

 My Centurion amp is drawing negative grid current and has no power
output. I have checked the power transformer, diode string and filter
caps and verified with an external VOM that I have 3000vdc on the
plates. I have also changed the tubes, no improvement.

 Any thoughts as to the root cause? I had replaced the pesky bias
transistor 5 years ago when the unit would not key in transmit. The
symptoms are different now, since the unit will go into transmit when
keyed by my xcvr.

 Appreciate any thoughts. My Centurion is 27 years old.

 Thanks and 73,
 Dave, K2DP

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