Here, the 15 uh safety choke is installed across the ceramic vac load cap
on the output side. This DC grounds the entire PI output tank circuit at
all times. IF any of the 4 x plate block caps ever failed shorted, or semi
shorted, you don't want 5.5 kv getting onto the tune + load caps, vac TR
relay's, coax between TR relay's and output connector, nor going up the
coax to the ant array. You want the entire tank DC grounded anyway, so the
plate block caps act like plate block caps...IE: they will still have a
tiny leakage due to high internal leakage resistance.
18 ga magnet wire used for the safety choke, wound on 1" solid Teflon rod.
Mounted to sidewall with a 1/4-20 screw. Cold end of choke is bonded to the
sidewall. Teflon wire used to wire hot side of safety choke...to the NO
contact of the vac output relay assy. The NO of the output relay is
directly bonded to the vac load cap.
I see in a lot of HF / 6m amplifiers, both commercially built, and also
HB, they will use a pie-wound safety choke...like a 2.5 mh type. The
problem with that is.... the DC resistance of the choke is typ 25-40
ohms. IF the plate block cap assy fails shorted, the pie-wound safety
choke will not handle the entire fault current...and simply explodes. I
have seen them blown to bits a few times over the years.
The safety choke is installed at the 50 ohm end of the tank circuit. It's
XL does not have to be high. 50 uh is ample on any 160-10m amp. 10-15 uh
is ample on a 6M amp.
This latest video also shows the coax wiring to the input ceramic vac
relay, which also includes the bypass leg, and also the input going back
towards the SO-239 input coax connector.
https://www.youtube.com/watch?v=r_jxiYM7bcs
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