Hello
I think and hope that my problem with parasitics in FL-2100B is now solved
with the help from this AMPS-reflector.
>From Rich Measures, AG6K I got some useful advice and a suppressor kit for
2pcs 572B´s.
Here is what I did:
1. Anode circuit
¤ 2 NiCr suppressors installed in each anode.
6 turns in parallel with 100 ohm 3Watt Metal Oxide Film resistor (MOF)
¤Original silvered strap from C-blocking to C1-tank replaced with 2 NiCr
wires, one straight, the other with 1 turn 6mm diameter.
After these modifications no VHF-resonances could be detected. Before I had
a well-defined dip around 105 MHz.
2.Grid circuit
¤ 200pF decoupling conds replaced by 2x470pF from each grid directly to
ground lug at the socket mounting screw.
¤ Original 33 ohm grid resistor removed and replaced by 33 ohm and 10 ohm
in series. 10 ohm to grid. On each wire of the 10 ohm resistor I placed a
ferrite bead, my=125, mix 61. Resistors are 2W MOF.
3. Cathode (filament) circuit
¤ From input network switch to each filament I used 10nF in series with 10
ohm 3W MOF.
4. Misc.
¤ Glitch protection diodes installed in parallel with plate meter "shant"
R3. 2 diodes type 1N540x in series, anode to ground.
¤ Filament voltage now 6,0VAC at socket. In my case I used the 234v tab on
the primary of T1. This to increase tube life.
¤ On all bands I have 500+ Watts with the amplifier driven to 400mA.
I am gratefull to Rich, AG6K for his advice and help. I think Rich has made
a great contribution towards our better understanding of VHF-parasitics.
73
Hans, OZ5DX
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