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Re: [Amps] 4CX250B Ratings in Dentron Clipperton V

Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V
From: "Bill, W6WRT" <>
Date: Sat, 22 May 2010 21:19:14 -0700
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On Sat, 22 May 2010 17:00:15 -0400, Rob Stampfli <> wrote:

>Never having had a tetrode amp, I feel compelled to ask:  Should you
>always tune such an amp for a peak reading (within the acceptable
>range for screen current) and not add a tad bit of loading for linearity,
>as one normally should for a triode amp?  (If you're going to add some
>load anyway, what is the advantage of having that nice sharp peak?)


The first time you tune either a triode or tetrode, you should start
with a very small amount of drive, adjust both tune and load for
maximum power out, increase the drive a small amount, adjust tune and
load for max output, and repeat again and again until you reach full
desired power output. At that point, adjust the tune capacitor while
watching for a peak in grid current (control grid for triodes, screen
grid for tetrodes). The grid current is a more sensitive indicator or
correct tuning than the power output meter.  Readjust the load control
for max output and make a mental note of the value of the grid current
and plate current at that point. 

The next time you tune up, you can pre-set the tune and load
capacitors (assuming you have a dial or turns counter) and apply a
small amount of drive. Adjust the tune cap for max grid current and
then increase drive while watching plate current. When the plate
current reaches the previously noted maximum, you are essentially
tuned up. If necessary, tweak the tune cap for grid current peak and
tweak the load cap to set the value of the grid current peak. You are

If you wish, you can increase the loading a bit (less grid current) to
increase the headroom if running SSB to prevent clipping. Not
necessary for CW, RTTY, FM  or any constant-carrier data mode. 

Takes longer to tell than to do. 

73, Bill W6WRT
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