[Moon] Amplifier technical questions

[Oene Spanjer]

Hello All (amplifierbuilders)

Recently I have build a 2 m amplifier with 2 x GI7b but experience 
some troubles.
I have build this amplifier with separate bias control, so I can
adjust each tube separately and therefore the cathode 's are 
not connected as seen in all the 2 tubes designs but each tube
get's it's input RF via a capacitor.

First I build an amplifier with stripline according to G4DCV his
design, but got only few Watts out. 
Then I rebuild the design to the 'lazy builder' design of YU1AW
to see if the tubes (NOS) were still 'alive'  and yes they were;
I am able to get somewhat 700 Watts out at abt 40 - 50 W input,
so the tubes are doing as expected.

But with this design consisting of  2nF / 30kV from anode
to coil and tune cap to earth and output coupling by another
variable capacitor,  I experience that is is extremely sharp and
when the amp starts getting warm I have to retune every time
I am on the air again.  Output  drops each sequence to the 50W 
level and this is in practice not working.
Also at some points of chancing the output coupling C it starts
sparking and that is really bad. 1 C has already got black
and those RF voltages must be huge !!

Now I am thinking of rebuilding this to a version with stripline.
My anode chamber is not that big so I guess have to play 
with the dimensions.

My questions: Does anyone have had those experiences and
does a stripline gives me a 'flatter' resonance so I have not
to retune that often ?
My single GI7b has also a stripline ( DJ9HO design ) and 
when it has warmed up I only have to retune very little, so I
guess a stripline is much better ( it even gives some extra
cooling surface )
And how are the stripline dimension influenced by the 
dimensions of the anode chamber ?  I read that the distance
from bottom to stripline and also from stripline to top are
important for the dimensions.

I hope anyone has some answers because it's sad having
the capability of medium power but still can't use it :-(

Thanks all for reading and GL

73 Oene
PA3CWN




-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.df6na.de/pipermail/moon/attachments/20070210/f80aba8d/attachment.html