10 KW CCS ON 6M...USING THE 3CX-6000A7... PART 14
Here the L-PI network required some minor tweaking on the main PI coil,
between the 2 x vac caps. After 3 x tweaks, scott nailed it. Some other
minor issues were resolved. Temp 1k ohm load resistor was wired between
anode and rear wall to simulate the plate load Z. (5500 vdc load @ 3 amps).
Analyzer on the output 7-16 DIN connector, and all 4 x vac relays operated
with an external supply.
Tune and load ceramic vac caps initially tweaked for 1:1 SWR on 50 mhz,
then again on 54 mhz. Success at last, and it tunes the entire 6M band
nicely.
The bypass SWR was 2.5:1 so a 33 pf cap was temp wired between the NC
contact of the output relays..to chassis. That reduced the bypass SWR down
to 1.5:1 It will probably have to be increased to aprx 50 pf for a 1:1
bypass SWR, and a NPO HT-50 style cap will be used for this function.
Bypass SWR is just the amplifier in standby mode, with a 50 ohm Load on the
output connector, and the analyzer, this time, on the input..and all TR
relays NOT operated. The input is routed to the output via the NC contact
(bypass leg) on both the input + output relays. ( jumpered together via
RG-400).
The relays only switch the center conductor of the coax, and on upper HF,
and esp 6M, will introduce XL..... which will cause the bypass SWR to rise.
Hence the (aprx) 50 pf cap to introduce just enough XC, to cancel out the
XL. We may also add a small choke in parallel with the bypass cap, to DC
ground the center conductor of the coax on RX. The safety choke across the
load cap also grounds the center conductor...but only on TX.
Stay tuned for tomorrow's part 15 video.
https://www.youtube.com/watch?v=r3YscGkooa8
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