Damien,
"Load" button on 160m is always at "0" "ccw" even on 1810khz or 1900khz,
just the "plate" get some influence "1" in CW part and "3" at 1850 for
example.>>>
This indicates not enough loading capacitance or not enough tank inductance,
especially if plate current is high and grid current low.
Low or inadequate operating Q is indicated by a load control working
backwards from normal, or having no effect at all as you move the control.
Current IP at 500mA give 400w out on 160m , 700w on 80 and 40m ...
still until 550w on 10m but the PA only used on 160m , sometimes on 80 but
rare.>>>>
Indicates lack of loading capacitance, especially if grid current is also
proportionally low.
For 90w IN : 1810Khz 440w 1900Khz 490w load 0 plate0
at 1810/ 3 at 1900 but 550mA current for this for + 100 good
watts in.
So more power on higher frequency on the band.>>>>
Indicates lack of loading capacitance or tank inductance.
PA0FRI on his website , on his article about the fl2100z you can read :"The
lower output on the 160 m band is due to the very low Q of the anode
circuit, because the manufacturer has cut the components. The lower power on
the higher bands is due to the decreasing efficiency of the tubes and the
higher circuit losses on the higher frequencies.">>>>
I would not trust a thing on that website.
Anode operating impedance is closely RMS RF anode voltage^2 / Pout = Rp
Approximately 1700^2 / 600 = 4800 ohms at 600 watts
Looking at the FL2100 values, it looks like they have a loaded tank Q in the
20's. They have unnecessary high Q, not too little. This is why they run out
of loading capacitance. They need almost 3500-4000 pF with that operating Q.
You could add shunt capacitance. The only ill effect would be lack of range
(delta C) in the controls because of the large padding capacitances.
The actual cause is from lack of tank inductance on 160 meters. While you
can work around that by increasing padding capacitance, a better solution
would be to increase tank coil inductance on 160 meters. You might add a
small toroid inductor like a T-200-2 between the 160 meter end of the coil
and the switch/loading cap connection.
If that were my amp and I wanted to test this, I would temporarily stick
a -2 iron core in the cold end of the tank coil and see if output increases.
This would prove the benefit of more inductance (which would actually reduce
tank operating Q).
Many amplifiers of that age, because of size required for 160 meter coils,
did not have enough tank inductance. This is very common for Dentron and
others. Some have close to the proper inductance with the cover removed, and
when the cover is installed the inductance falls too low. While it is unsafe
and should never be done, sometimes removing the cover restores performance
by increasing tank inductance when the coil is near the cabinet. Dentron is
bad about this.
73 Tom
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|