On 24 January 2012 02:30, Paul Decker <kg7hf@comcast.net> wrote:
> Hi gang,
> A few weeks ago I asked the group about modification to my 8874 stripline
> 432 MHz amplifier to replace it with a 3cx800.
>
> Well I made the modifications and extended just the very back portion of
> the stirpline. I couldn't get the amplifier to tune up. Grid and plate
> current were well within spec, but i would not output much more than 50
> watts.
>
> It was mentioned to use a gdo or antenna analyzer to tune the stripline.
> I'm wondering what the procedure for that might be? How would I couple
> the gdo or antenna analyzer to the stripline? With or without the tube
> installed? Power on/off?
>
> Thanks,
> Paul
> kg7hf
>
1) Install the tube.
2) Have the power off
3) Put the GDO near the stripline and find the dip.
4) Gradually move the GDO further from the stripline. The dip will get
weaker as the GDO is couples less strongly to the anode line. But the
frequency of the dip will be more accurate, as the anode line wont effect
the measurement as much. You want to have the coupling as weak as possible,
although it must not be so weak that you can't find the position of the
dip.
There might be some advantage in putting a resistor between the chassis and
the anode of the tube, equal to the load impedance of the tube I must admit
I've never done that, and managed to get the above procedure to work,
though I think there might possibly be some advantage in this, as it more
closely represents the running conditions of the amp.
Dave, G8WRB
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