<I got all the parts in and am building the board.

<I installed all the relays, the 10 meter A and B trimmers and the wound a toroid. 7 turns of 20 AWG

<With a dummy load on output of 50 ohms and the analyzer on the input:

<with 10 meter relay closed, I can tune the trimmers to get a dip of 1.0 at 56 ohms 28.500.? ?I am using LESS cap than the Chart says. It says 100PF, 7 turns and 100PF.? I am at 25 to 35 PF on each in and out cap.

<Question

<What is the expected behavior if I roll the Analyzer down to 20 meters?? ?

<I do NOT SEE A BAND PASS for the 10 meter position. I only see matching and a HIGH PASS.? If I try to go past 40MHZ the SWR shoots up high.

<If I go LOWER in frequency the impedance will move but its fairly flat

<Is this expected behavior????

<C

## I design and run the PI tuned inputs through software every other week...then verify on the bench.? For a overall network Q? of '4'? (input Q = 2....and output Q =2)? ?on 10m,(28.5 mhz) when matching 50 ohms from xcvr to 50 ohm tube input Z....?it should be 223.4 pf? - .22 uh? - 223.4 pf.?

## For an overall network Q of? ? '1.8'? (input Q =.9......and output Q = .9) on 28.5 mhz, it's then 100 pf - .28 uh - 100 pf.?

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##? if ur caps are only 25-35 pf, then ur Q is through the floor...and the coil has way too much uh.?

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## either remove a turn or maybe 2, and? / or spread the turns? a bit.? Tweak the coil till both caps are in the 100-140 pf range.? Ok, at that point, you will see the 1:1 swr @ 28.5 mhz..... which should remain flat between? 28.0? and 29,0...then rise when u go below 28 mhz...and above 29 mhz.

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##? with the Q through the floor, it all goes to hell...and you won't get a? proper bandpass response.?

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## Have u tested al the other bands yet ?? ? IE: installed caps and toroid's for the other bands...and tested other bands.?

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##? Note on the above,? only when matching 50 ohms to 50 ohms? (or any 2 x equal Z's)? is the C1 + C2 caps both the same value.? On software, we only tweak the overall network Q.? ?The C1 input Q? ?+ the C2 output Q = overall network Q.?

##? For a PI network for the kw output side, (High tube Z? down to 50 ohms), typ an Overall network Q of....'12' is used....which consist of an input Q of 10...and an output Q of 2.??

##? In the old ARRL books (and also Eimac's? 'care + feeding'), they only used the INPUT Q...which is why they said? to use a Q of? '10'.? ?They did the same thing with PI tuned inputs.? When they said to use a Q of..'2'? ?what they really meant was to use an overall network Q of 4.?

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##? For tuned inputs that are tweaked once ..in the middle of the band,? you want low swr? across the entire band.? ?500 khz on 80m is like 1mhz wide on 40m..and 2 mhz wide on 20m..and 4 mhz wide on 10m.? This is where you can do some creative tweaking.? Each band is different....with 160m only 200 khz? wide, 80m = 500 khz, 40m = 300 khz, 30m = 50 khz,? 20m = 350 khz, 17m = 100 khz, 15m = 450 khz, 12m = 100 khz, 10m = 1700 khz.? ( 6m = 4000 khz).
Then factor in if the tuned input has to cover? 10+12 m...... or 15 + 17m.? ?The best u can do there is to tweak it so it's flat swr at the midpoint between 10+12m.... and ditto with 15 + 17m.?

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## here is the other thing u gotta worry about.? The tube's input C? is directly in parallel with the C2 of the tuned input. Say a 3CX-3000A7.... with it's 38 pf input C (grid to cathode C).? Now you have to subtract 38 pf from the calculated C2 values of ALL the various tuned inputs for each band.?

##? here's the other thing to deal with.... the XL of the bifilar fil choke (since it's RF grnded at it's cold end...and hot end of fil choke goes to the cathode) is also directly in parallel with the tube's input cathode to grid C.?

##? On a SB-220, they used a 9 uh (per winding) fil choke.? ?XL @ 3.75 mhz =? 212 ohms.? ?You now require 212 ohms of XC to cancel out the XL.? ? 200 pf @ 3.750 mhz = 212 ohms of XC.? On an SB-220, the C2 cap of the 75m tuned input has to be increased by 200 pf? vs it's calculated value.? But since the tube's input C on a pair of 3-500Z's is 16.6 pf,? it's then 200-16.6 pf =? 183.4 pf.

## The fil choke primarily affects the lower bands. On the upper bands it's less of an issue.? ? 9 uh is 1611 ohms of XL @ 28.5 mhz.? ? ? 3.465 pf = 1611 ohms of XC.? ? ?That amounts to dick on 28.5 mhz...and the pair of 3-500Z's still has 16.6 pf...so now it's 16.6 - 3.465 pf = 13.135 pf.? 13.135 pf has to be subtracted from the calculated C value of the tuned input.

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##? If you are doing say a PI network for a 3CX-3000A7,? wire the relay switched tuned input? into the cathode.....and temp wire a 50 ohm resistor between one cathode lug....and chassis....and also plug the tube into the socket.? With no fil or B+, all voltages off....and TR relays activated, put ur analyzer on the input...and tweak both arco's for each band for 1:1 swr.? ?50 ohm resistor removed.? Apply B+ and fil V.... and test the amp.? ? It will be sorta close, and perhaps some minor C1 + C2 tweaking required.? That depends on drive level, bias used,? loaded B+ used, amp tuned to max PO.... and perhaps loading increased till PO drops 1-2%, and cable length between xcvr and input to amp.?

##? if the relay switched, tuned input board is below the chassis, near the cathode, it may or may not be possible to tweak all the arco caps.? ?The board would have to be mounted to rear apron, with holes to access the caps..or to chassis..pita.

If amp is fan cooled, you might be able to remove bottom lid.? If a chimney is used, removal of bottom lid means? zero airflow.??

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##? This is why I went to the pair of broadcast caps + tapped coil, manually tuned, tuned input setup on the hb amps.?

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Jim? ?VE7RF