Regarding the plate choke (thanks again Nomad) I compared with my old choke and found that it was roughly twice the inductance of W8JI's component so I'm hopeful that I'll see improvement. Over the past 2 months I replaced the point to point wiring of the RF Input I had strewn about the tube sockets. I used a small breadboard with traces that reduced lead length and made it easier to remove/adjust. Replacing the 5 position switch w/ 11 position ceramic gives more matching combo's. SWR analyzer on input looks good: swr of <2 from 10-80 (encouraging) but there's more to input matching than swr. Exactly how the match goes from 450 ohms from the 1:9 trifilar unun to a 750 ohm resistive match still eludes me as does the net affect from adding another tube but..... I'm making progress if only by narrowing the range of possibilities.
The only commercial 2x 4cx300a amp I found was the Hallicrafters HT-33. The drive is series connected to a 9-198mmfd variable cap and then a series .047 ceramic to join with the Bias voltage (which comes from a 22k 1w resistor) and that drives the control grids after passing through suppressor-type, 47R resistor/coil combo for each tube. A recent Post (http://lists.contesting.com/archives//cgi-bin/mesg.cgi?a=Amps&i=4A691069.4000205@rogerhalstead.com) reported only 625w max from the Hallicrafter. Seems rather low but those early amps (1950-60's) had different ways of measuring PO so it may be apples & oranges.
I'll have amp sealed-up again soon. My antennas working really good w/ new coax and mast-mount relay. It takes a lot to keep it all working.
neil, NYC
The only commercial 2x 4cx300a amp I found was the Hallicrafters HT-33. The drive is series connected to a 9-198mmfd variable cap and then a series .047 ceramic to join with the Bias voltage (which comes from a 22k 1w resistor) and that drives the control grids after passing through suppressor-type, 47R resistor/coil combo for each tube. A recent Post (http://lists.contesting.com/archives//cgi-bin/mesg.cgi?a=Amps&i=4A691069.4000205@rogerhalstead.com) reported only 625w max from the Hallicrafter. Seems rather low but those early amps (1950-60's) had different ways of measuring PO so it may be apples & oranges.
I'll have amp sealed-up again soon. My antennas working really good w/ new coax and mast-mount relay. It takes a lot to keep it all working.
neil, NYC
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