[TenTec] Care and Feeding of Centurions

[Bob McGraw - K4TAX]

I fully agree with Jim on the point that grid current is the most critical 
value to watch and adhere to in terms of extending tube life.

For a pair of 3-500's the total grid current should NEVER exceed some 230 to 
260 mA MAX!    This is in tune mode with carrier.  Operationally, with SSB 
the grid current meter would typically display 100 to 130 mA on voice peaks. 
Plate current in tune with carrier, should be between 700 mA and 800 mA MAX 
and with SSB, the plate current meter would typically display 300 to 350 mA 
on voice peaks.  If ones amp while in SSB operation is exceeding these 
values, likely the tuning is not correct or the amp is being overdriven.  In 
either case, it is bad for the amp and worst for the stations on either side 
of your frequency.

If you wish to operate at less than rated or maximum power, always tune the 
amp for maximum rated power using the correct values for grid current, plate 
current and power output.  Then simply reduce the drive to attain the 
desired operating power.  NEVER retune the amp for the lower power value.

I'll say this and likely get in a bit of hot water with some folks 
but..........for those that profess to "dip the plate",  this is correct for 
a Class C amplifier, but NOT SO for a linear amp in Class AB1 or Class AB2 
service.  Always tune for maximum output.

We'll not discuss "tuning to the right side of resonance" as it applies to 
the tuning a Class C amplifier.  However, you old BC folks will certainly 
understand this term.

73
Bob, K4TAX








----- Original Message ----- 
From: "Jim Brown" <k9yc at audiosystemsgroup.com>
To: <tentec at contesting.com>
Sent: Sunday, February 02, 2014 2:31 PM
Subject: Re: [TenTec] Care and Feeding of Centurions


> On 2/2/2014 12:03 PM, Bob McGraw - K4TAX wrote:
>> Proper tuning and loading and proper drive is the key to success for long 
>> amp and tube life.
>
> And also the key to having a cleaner signal. An amp that is over driven 
> (using AGC to control the drive power) or that is not well tuned will 
> generate lots of splatter, clicks, and other trash.
>
> I don't know about the 3-500Zs used in the Centurion, but the key to long 
> life for the ceramic triodes used in the Titan is to keep the grid current 
> below its limits at all times. My objective is to keep the grid current 
> below half it's rated value, and my tubes last a LONG time. Grid current 
> is minimized when the amp is well tuned and not overdriven.
>
> 73, Jim K9YC
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