Tom wrote;
>Exactly. Let me tell you what I've been doing the past few months.
>I put a 1200Z7 in an RF deck of the AL1200, and with multiple
>fingerstock contacts the tube was totally stable with no
>suppression at all. That allowed me to add inductance between the
>tube and the tank, to reduce Q on ten meters and bring efficiency
>way up. The only reason that works is because the Z7 has virtually
>zero grid impedance to the chassis. A 1200A7 will oscillate like
>crazy with no suppression, or with suppression and that series coil.
>
>
>I did the same to a 3CX800A7. I added a grid collet instead of a few
>fingers on the grid, and I could remove all suppression on a
>3CX800. That let me use the same technique to put an AL-800
>amp on six meters (bandswitched from 160-6 meters) and get 1200
>watts out on six meters!
>
>
>I have a 3CPX800A7 with 3000 volts on the anode, no suppression,
>a VHF Q of over 1000 in the tank system, and it is completely
>stable. That PA runs 1100 watts out on 2 meters with 30 watts of
>drive, and is rock stable. The reason? The grids are very well
>grounded both inside and outside the tube. The grid "problem" is far
>above the operating frequency so stability isn't an issue.
Its sounds like you have found the an answer to what I thought was a
imaginary problem if what you say is true and I dont doubt that it is then
I would hope these improvements would be on the very next series of
Ameritron amps, the word would soon spread about the improvements. Market
share would no doubt increase and Rich's customer base would dwindle. A
simple kit could be devised for the adventurous ham or factory up grades
could be done for minimal cost or free ala Ruger Arms. the debate would be
moot and of no interest . I don't say these things sarcastically, as a
consumer I dont take spending 1000.00 to 3000.00 dollars on anything
lightly and when I do I expect it to be plug and play not the parts list
for my next science experiment in RF design. If there are simple design
changes that eliminate these problems that have been discussed ad infinitum
then they should be incorporated no matter who is right or wrong about the
cause of these problems. Then the debates could focus on the best designs
to build homebrew amps and not repair and redesign store bought
equipment that shouldn't even need the covers off for several years. This
is not meant to be an indictment of Ameritron only a review of the
archives leaves no manufacture untouched the kenwood 922 as a recent
example. I for one am very interested in the info that you have garnered on
the 1200Z7 I am putting together the makings of a RF deck using two of
these tubes.
sincerely
Dave / WB0PKK
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