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@audiosystemsgroup.com>
To: <tentec@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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