Loading a bit heavier than the peak works with any tube or configuration.
Since you are decreasing the loading capacity you are also decreasing screen
current. Good tetrodes will also have their power peak long before maximum
allowable Isg is reached, something it shares with the triode as an
indicator of the tubes health. I run my stock (driven by a HT-32B in the
vintage SSB station) and also the 6M NCL-2000's at about 10-15ma Isg for
1200-1300W out which is at the peak.
Carl
KM1H
----- Original Message -----
From: "Rob Stampfli" <rob@cboh.org>
To: <amps@contesting.com>
Sent: Saturday, May 22, 2010 5:00 PM
Subject: Re: [Amps] 4CX250B Ratings in Dentron Clipperton V
> On Sat, May 22, 2010 at 04:27:11PM -0400, Roger wrote:
>> On 5/22/2010 1:22 PM, Jim Brown wrote:
>> > On Fri, 21 May 2010 19:32:43 -0400, Roger wrote:
>> >
>> >> The screen is the most sensitive tuning indicator and particularly so
>> >> at
>> >> the higher power settings.
>> >>
>> > So if I watch the screen current, am I tuning for minimum?
>>
>> In the final stages of tuning a Tetrode amp you are peaking the screen
>> current with the loading control. This peak coincides with maximum
>> output, or should and is a sharper peak than the output.
>> If the screen current is excessive, back off on the drive a bit and
>> retune. The max screen current should also come with minimum grid
>> current for any specific drive. IOW, increasing screen current decreases
>> grid current.
>
> 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?)
>
> Inquiring minds.
>
> Rob
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