A few month ago, I have discuss with a friend about a pair 572Bs work in
6m,in usually, the people don't think some PAs like FL-2100 and SB-200 what
with 2X572Bs can not work in 160(80)m-6m, 6m only.
I have some thoughts about these PAs, maybe can modify and let these PA
work in 160(80)m to 6m . 1) add a relay and swicth in/out 6m input network
indendently and let the wire what connect to the cathoude as short as
possible.
don't modify the exist input network.2).I do know 572B with long lead.
to add a FR4 PCB or metal sheet what with two holes in the top of tube
's base/bottom of anode(actually insert the tube into the holes) ,
connect / solder the sheet /PCB to ground . this sheet for shield
cathoude/anode.
3)in 6m band , duo to the 572B's large capacitance, you can not get
resonable QL,if cut the plate capacitor,and regard the tube 's output
capatance +stray capacitance as plate capacitor(fixed), insert a shorted
copper circle in the coil
to turn the PA like
http://www5a.biglobe.ne.jp/~jh2clv/gu74b2m/2mplatecoil030920.jpg. this can
solve the problem what 572B's large output capacitance
problem.3)certainly, the neutralization is needed.
I do not have FL-2100 and SB-200, If you interested, maybe you can try to
add 6m band and HF bands still usuable.
Any suggestion?
73!Hsu
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